Karstology in the Classical Karst (Advances in Karst Science) 3030268268, 9783030268268

Citation preview

Advances in Karst Science

Martin Knez Bojan Otoničar Metka Petrič Tanja Pipan Tadej Slabe Editors

Karstology in the Classical Karst

Advances in Karst Science Series Editor James LaMoreaux, Tuscaloosa, AL, USA

This book series covers advances in the field of karst from a variety of perspectives to facilitate knowledge and promote interaction thereby building stepping stones in this process. Methodologies, monitoring, data analysis and interpretation are addressed throughout the wide range of climatic, geological and hydrogeological contexts in which karst occurs. Case studies are presented to provide examples of advancement of the science. Issues to be addressed include water supply, contamination, and land use management. These issues although occurring on a local basis share many of the same features on the global stage. This book series is a critical resource to the scientific community allowing them to compare problems, results, and solutions. The presented information can be utilized by decision makers in making decisions on development in karst regions. Contributions presented may be used in the classroom and to work with stakeholders, scientists, and engineers to determine practical applications of these advances to common problems worldwide. The series aims at building a varied library of reference works, textbooks, proceedings, and monographs, by describing the current understanding of selected themes. The books in the series are prepared by leading experts actively working in the relevant field. The book series Advances in Karst Science includes single and multi-authored books as well as edited volumes. The Series Editor, Dr. James W. LaMoreaux, is currently accepting proposals and a proposal document can be obtained from the Publisher.

More information about this series at http://www.springer.com/series/15147

Martin Knez • Bojan Otoničar • Metka Petrič Tanja Pipan • Tadej Slabe

•

Editors

Karstology in the Classical Karst With Contributions by Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, Nadja Zupan Hajna

123

Editors Martin Knez Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute Postojna, Slovenia

Bojan Otoničar Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute Postojna, Slovenia

UNESCO Chair on Karst Education Vipava, Slovenia

UNESCO Chair on Karst Education Vipava, Slovenia

University of Nova Gorica Nova Gorica, Slovenia Metka Petrič Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute Postojna, Slovenia

Tanja Pipan Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute Postojna, Slovenia UNESCO Chair on Karst Education Vipava, Slovenia

UNESCO Chair on Karst Education Vipava, Slovenia Tadej Slabe Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute Postojna, Slovenia UNESCO Chair on Karst Education Vipava, Slovenia

ISSN 2511-2066 ISSN 2511-2082 (electronic) Advances in Karst Science ISBN 978-3-030-26826-8 ISBN 978-3-030-26827-5 (eBook) https://doi.org/10.1007/978-3-030-26827-5 © Springer Nature Switzerland AG 2020 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Technical editing done by Alenka Možina This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

As karstologists in the country of the Classical Karst, we are striving to develop Slovenia’s Karst Research Institute as one of the leading international karstology research and education centres. Almost half of Slovenia is karst and more than half of its water supply comes from karst aquifers. We are developing a comprehensive science of karstology incorporating all of its most important fields. With the goal of understanding the three-dimensional karst landscape, we link interdisciplinary research of the karst surface, caves, waters, and ecology, a unique approach that is also our international advantage. We are developing karst geography, geology, geomorphology, speleology, hydrogeology, biology, and microbiology. We connect field studies (including the establishment of monitoring networks and long-term measurements of water, cave climate, etc.) with laboratory investigations and laboratory and computer modelling. Lithological studies of carbonate rock are led by Martin Knez, structural geology by Stanka Šebela, and paleokarst by Bojan Otoničar; Nadja Zupan Hajna and Andrej Mihevc focus on the development of the surface, karst caves (with sediments), and karst as a whole; Tadej Slabe connects studies of cave rock and surface forms; cave and aquifer research employing mathematical modelling is being developed by Franci Gabrovšek, Matej Blatnik, and Cyril Mayaud, and hydrological studies by Metka Petrič, Nataša Ravbar, Blaž Kogovšek, and Janja Kogovšek; Mitja Prelovšek is focusing on geomorphic, hydrochemical, and meteorological aspects of present-day speleogenetic processes; research on subterranean biology section is run by Tanja Pipan and microbiological by Janez Mulec; Magdalena NăpăruşAljančič connects the development of our part of European infrastructural network, and Trevor Shaw coordinates study of history of karstology and speleology. David Culver comes from American University in Washington DC and Hong Liu from International Joint Research Centre for Karstology of Yunnan University. At the international level we are expanding the basic knowledge of karst that serves as a starting point for the rational planning of life in vulnerable regions; participating in numerous directly useful projects involving water supply and conservation, the planning and construction of traffic routes, etc.; and developing and providing courses for university students. We carry out Slovenia’s primary Karst Research Program. We lead and participate in numerous domestic and international projects. At the University of Nova Gorica we offer a Doctoral study in karstology that is the only one of its kind in the world and also acts as UNESCO Chair on Karst Education. We work together with karstologists from around the world. We initiated the foundation of the International Karstological Academy and continue to direct its work. We organize the International Karstological School “Classical Karst”, the largest international annual conference of karstologists. The Karst Research Institute also hosts the seat of the International Union of Speleology. Together with Yunnan University in Kunming in the province of Yunnan in China we established the International Centre for Karst Research. We publish Acta carsologica, one of the world’s leading karstological scientific journals, and edit the karstological anthology Carsologica. We assist in the development and promotion of karstology in numerous countries around the world. The two latest books published in this collection (The Beka-Ocizla Cave System, Karstological Railway Planning in Slovenia, 2015, and Cave Exploration in Slovenia, Discovering Over 350 New Caves During Motorway Construction on Classical Karst, 2016) were devoted v

vi

Preface

to developmental challenges on karst. This book is a part of the fundamental karst research, which remains the primary mission of the Institute even at its 73rd anniversary. We have selected the most important recent research findings. In our research, results of which are presented in this book, we cooperated closely with Tatiana Akimova, Asma Al-Farraj, Pavel Bosák, Wolfgang Dreybrodt, Manuel Roberto Gutiérrez Domech, Jože Janež, Naško Janež, Jernej Jež, Igor Kalmykov, Luiz Eduardo Panisset Travassos, Petr Pruner, Josip Rubinić, Rosario Ruggieri, Ela Šegina, Nataša Šimac, Mirka Trajanova, and Kazuko Urushibara-Yoshino. Postojna, Slovenia

The Editors

Acknowledgements

The authors acknowledge the Karst Research Programme (research core funding No. P6– 0119), the research projects (J7-7100: Natural resources of karst show caves: a balance among protection, exploitation, and promotion; J6-8266: Environmental effects and karst water sources: impacts, vulnerability and adaptation of land use; L1-7555: Development and application of method for quantity and quality assessment of ground-water resources in karst; L6-9397: Methodology for monitoring the sustainable use of karst show caves with automatic measurements—role model—Postojna cave; L7-8268: Karst research for sustainable use of Škocjan Caves as World heritage) and the Young Researchers Programme financially supported by the Slovenian Research Agency. Additional financing was provided by the Public Service Agency Škocjan Caves Park, the company Postojnska jama d. d., and the public companies Komunala Kočevje and Kovod d.o.o. Some of the results presented were achieved in the frame of the European projects: EPOS Implementation Phase and EPOS Sustainability Phase (H2020-EU.1.4.1.1. Developing new world-class research infrastructures), RI-SI EPOS and RI-SI-2 LifeWatch (Operational Programme for the Implementation of the EU Cohesion Policy in the period 2014–2020, Development of Research infrastructure for international competition of Slovene Development of Research infrastructure area—RI-SI, European Regional Development Fund, Republic of Slovenia Ministry of Education, Science and Sport), eLTER H2020 (H2020 INFRAIA and H2020 INFRADEV Advance eLTER), eLTER RI (Long-Term Ecosystem, critical zone and socio-ecological systems Research Infrastructure; ESFRI 2018 Roadmap), LifeWatch ERIC (e-Science and Technology European Infrastructure for Biodiversity and Ecosystem Research), GEP and Škocjan–Risnjak (European Regional Development Fund Cross-Border Cooperation Programme Slovenia–Italy and Slovenia–Croatia 2007–2013). Research was included in the framework of the UNESCO IGCP project No. 661 and UNESCO Chair on Karst Education. The authors acknowledge Leon Drame, Franjo Drole, Grega Juvan, Peter Kozel and Borut Peric for field work assistance, Mateja Zadel and Sara Skok for laboratory support. We would like to thank reviewers Gregor Kovačič, Barbara Luke, Andreea Oargă-Mulec, Robert Armstrong Osborne, Lejla Pašić, Lukas Plan, Ira D. Sasowsky, Samo Šturm, Cheng Zhang. Translations and language editing was provided by Amidas d.o.o., Milena Djokić, Vanessa Johnston, Barbara Luke, Robert Armstrong Osborne, Ira D. Sasowsky, Wayne Tuttle. Graphical design was made by Tamara Korošec, and photos review by Igor Lapajne and Marko Zaplatil. Technical editing was done by Alenka Možina. We are also thankful to colleagues from Yunnan Institute of Geography, Yunnan University. Research of stone forests has been enabled by Stone Forest Research Centre of Stone Forest Scenic Spot Administration, Yunnan, China.

vii

Contents

1

Structural–Geological Mapping of Karst Areas . . . . . . . . . . . . . . . . . . . . . . . Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

2

Late Cretaceous and Paleogene Paleokarsts of the Northern Sector of the Adriatic Carbonate Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

1

11

3

Lithomorphogenesis of Karst Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

33

4

Significant Findings from Karst Sediments Research . . . . . . . . . . . . . . . . . . . Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

99

5

Measurements of Present-Day Limestone Dissolution and Calcite Precipitation Rates with Limestone Tablets in Stream Caves (with the Case Study of Škocjanske Jame) . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

6

Water Quality Monitoring in Karst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna ix

x

Contents

7

Planning Contamination Emergency Response Measures for Karst Water Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

8

Deciphering Epiphreatic Conduit Geometry from Head and Flow Data . . . . 149 Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

9

Microbial Underground: Microorganisms and Their Habitats in Škocjanske Jame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

10 Changing Perspectives on Subterranean Habitats . . . . . . . . . . . . . . . . . . . . . 183 Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna 11 Research Infrastructures and Karst Science . . . . . . . . . . . . . . . . . . . . . . . . . . 207 Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna 12 A Historical Overview of Development of Škocjanske Jame . . . . . . . . . . . . . . 213 Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

Contributors

Matej Blatnik Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia David C. Culver American University, Washington, DC, USA Franci Gabrovšek Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Martin Knez Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Blaž Kogovšek Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Janja Kogovšek Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Hong Liu Yunnan University, Kunming, China Cyril Mayaud Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Andrej Mihevc Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Janez Mulec Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Magdalena Năpăruş-Aljančič Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Bojan Otoničar Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Metka Petrič Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Tanja Pipan Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Mitja Prelovšek Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Nataša Ravbar Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Trevor Shaw Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia

xi

xii

Tadej Slabe Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Stanka Šebela Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia Nadja Zupan Hajna Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia

Contributors

1

Structural–Geological Mapping of Karst Areas Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna For understanding geological structure of karst areas (Palmer 2007), it is inevitably to have detailed geological maps. But karst areas are mostly geologically mapped only as parts of basic geological maps (1:100,000 in Slovenia). If we deal with the example of Slovenia, we need to stress that besides basic geological maps we have tectonic maps and sketches of smaller areas in SW Slovenia, which help to better understand the tectonic and geodynamic situation (Placer 1981, 1982, 1996; Placer et al. 2010; Čar 2018). And we have a geological map of the southern part of the Trieste– Komen Plateau (Cretaceous and Paleogene carbonate rocks) in the scale 1:50,000 (Jurkovšek et al. 1996). But detailed structural–geological maps of karst areas in the sense of Čar and Gospodarič (1984) are still rare. For understanding development of karst features, it is thus significant to make very detail structural–geological maps in scales as 1:5,000, 1:1,000 or even 1:500 of caves and of the karst surface. After the Second World War, karst areas of Slovenia were primarily studied by stratigraphy. In this sense, Pleničar (1960) described stratigraphic development of the Cretaceous rocks of the Notranjska region and determined that passages of the Postojna Cave are mostly parallel to the beds (Pleničar 1961). The dependence of the origin and formation of cave passages on the faults and fissures of the Postojna Cave, including the wider area of SW Slovenia, has been researched in particular by Gospodarič (1963, 1964, 1965, 1968, M. Blatnik
F. Gabrovšek
M. Knez (&)
B. Kogovšek
J. Kogovšek
C. Mayaud
A. Mihevc
J. Mulec
M. Năpăruş-Aljančič
B. Otoničar
M. Petrič
T. Pipan
M. Prelovšek
N. Ravbar
T. Shaw
T. Slabe
S. Šebela
N. Zupan Hajna Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia e-mail: [email protected] D. C. Culver American University, Washington, DC, USA H. Liu Yunnan University, Kunming, China

1969a, b, 1976). He produced detailed maps of the lithostratigraphic units of both the Postojna karst surface and underground as well as maps of the Postojna anticline structure together with the faults and fissures intersecting the anticline. In the SW Slovenia field mapping of karst surface expanded in 1980s in the scale 1:5,000 (Čar 1982; Čar and Gospodarič 1984). Čar (1982) divided tectonically fractured zones into fissured, broken and crushed zones regarding different intensities of tectonic change of the rock. In fissured zones, the carbonate rocks are least fractured, and stratification is still visible. Broken zone is more fractured zone where rock often occurs as blocks, which may be physically displaced. Crushed zone is most fractured where stratification has been destroyed and rocks are crushed to the degree of tectonic breccia and clay. Fractured zone properties may change from one pattern to another in horizontal and vertical directions (Čar 1986). By using the method of detailed tectonic–lithological mapping of the surface at a scale of 1:5,000, cave passages of the caves Planinska Jama, Črna Jama and Pivka Jama were connected with the already determined tectonically fractured zones on the surface with some degree of accordance (Čar 1982; Čar and Gospodarič 1984). In 1990s, the method of detailed structural–geological mapping was transmitted to karst caves, such as Predjama (Šebela and Čar 1991; Šebela 1996) and Postojna Cave (Šebela 1992, 1998) owing to good speleological maps. This was an important progress in understanding the formation of karst caves regarding the structural–geological elements. The mapping was carried out according to Čar’s (1982) classification of tectonically fractured zones. For the first time, this method was used experimentally in the cave passages and chambers of Predjama at a scale of 1:1,000. At a vertical distance of about 100 m, some tectonically fractured zones in the cave with outcrops on the surface by means of the longitudinal sections of the cave and those of the surface above were connected (Šebela and Čar 1991).

© Springer Nature Switzerland AG 2020 M. Knez et al. (eds.), Karstology in the Classical Karst, Advances in Karst Science, https://doi.org/10.1007/978-3-030-26827-5_1

1

2

After structural–geological mapping of Predjama, Postojna Cave was selected to be mapped in detail. An advantage of the Postojna Cave was its good cartographic base–ground plans, cross sections and longitudinal sections at a scale of 1:500 which were made by Gallino Petrini and Sartori in 1933–34, and supplemented by Hribar and Michler in 1948– 60 (Caves Registry). Additional modifications and improvements were made in 1972 and 1983–84 by Kenda, and were supplemented in 1989–98 by Drole (Caves Registry). Positions of Postojna anticline and interbedded slips due to thrusting and folding deformations were shown as important structural–geological elements that influenced the formation of cave passages. On the basis of the cross sections in the tourist part of Postojna Cave and those of the cave section of the underground Pivka River, it was established that 41.2% of the cross sections have been developed in tectonically fractured zones (Šebela 1998). The importance of selected bedding planes for the formation of phreatic channels was determined as well by Knez (1996) in the case of Velika Dolina collapse doline in Škocjan Caves. Surface structural–geological mapping was as well going on, and geological–structural position of vertical karst objects was presented for the area above Pivka and Črna Jama of the Postojna Cave system (Čar and Šebela 1997). Geological maps of the karst springs at the contact between non-carbonate and carbonate rocks in the Vipava Valley were presented by Janež (1997) and Janež and Čar (1997). Different cases of shaping of dolines regarding structural– geological conditions on the karst surface were shown by Čar (2001) and Šebela and Čar (2000). Development of karst at thrust contact limestone–dolomite was presented in 2001 (Čar and Šebela 2001). Based on detailed structural–geological cave maps, Šušteršič et al. (2001) determined that position of collector channels is dependent on deflector fault, which in Postojna Cave has a Dinaric trend (NW–SE). The collector channel gathers underground streams that should cross the broken zone of the deflector fault (Šušteršič 2006). Structural–geological map of the Škocjan Caves has been published by Šebela (2009). This was a compilation map of field mapping from the period 1991–2009 where field mapping represented big challenges due to high (up to 120 m) and big cave passages and due to the lack of good visibility. Connections between underground cave passages, structural geology and hydrology of water channels were shown with structural–geological mapping in the 1:5,000 scale above passages of the cave Kačna Jama near Divača (SW Slovenia) (Žvab Rožič et al. 2015). Recently, LiDAR tool is enabling important geomorphological upgrade for karst regions (Zlot and Bosse 2014; Mahmud et al. 2016), which helps geological field mapping

M. Blatnik et al.

but cannot completely replace it. By using LiDAR and UAV (unmanned aerial vehicle) in semi-arid Brazil karst fracture system, connection between development of karren features and fracture systems was shown (Silva et al. 2017). Detailed structural–geological cave and karst surface maps are the base for other karst-related researches as karst hydrology, chemistry of percolated waters in caves, geophysical research in karst (georadar, geoelectricity, seismicity), displacement monitoring of active tectonic structures, hydraulic modelling of karst areas, etc.

1.1

Case Studies

1.1.1 Longitudinal Geological Cross-Section Snežnik Mountain–Planina Cave In the case when a geological map is needed for understanding oscillations and direction of groundwater flow in the mountainous karst area, basic geological maps can help, especially if no other more precise geological maps are available and if there is not enough time or financial support to perform time-consuming detailed field geological mapping in forested and mountainous area. Here, we present the karst area of Snežnik Massif–Javorniki Mountains (Fig. 1.1) in SW Slovenia (Petrič et al. 2018) between Snežnik Mountain (1796 m a.s.l.) and Malni karst spring at the base of Planina polje (448 m a.s.l.), where carbonate rocks can reach the thickness of up to 3,300 m (Pleničar 1970; Šikić and Pleničar 1975). In tectonic sense, this area is part of External Dinarides. Thrust fault structure typical for NW part of External Dinarides is conditioned by paleogeographical conditions of the Adriatic–Dinaric carbonate platform (Placer et al. 2010). Thrust deformations started at the end of Cretaceous and especially after deposition of Eocene flysch. In the area of Snežnik Massif–Javorniki Mountains neotectonic structures as Predjama Fault as well as folds as secondary structures of the thrusting are detected. Faults show multi-phase tectonics with reactivations. This area is tectonically active (e.g. an earthquake on the western side of Javorniki Mountains in April 2014 with M = 4.4). The area was studied because of the location of Poček (Fig. 1.2), which is a military training area in Slovenia and completely belongs to karst (Kogovšek et al. 1999). A principal underground water flow from Poček is in the direction towards north to the Malni spring, which is a principal drinking water catchment for Postojna town. At Poček, carbonate rocks are tectonically broken in two principal fault orientations: NW–SE and NE–SW. For the vertical and horizontal water flow, the most favourable are tectonic zones in N–S and NE–SW orientations. Those are open fissures, which developed in relaxation tectonic conditions.

1

Structural–Geological Mapping of Karst Areas

3

Fig. 1.1 Course of longitudinal geological profile A–D (A Malni, B Poček, C Mašun, D Snežnik) on selected sector of basic geological maps 1:100,000 Postojna (Buser et al. 1967) and Ilirska Bistrica (Šikić et al. 1972). Legend 1 K2 2;3 —Cretaceous limestone with rudists and thinner dolomite layers; 2 1 K2 2 and 2 K2 1;2 — Cretaceous limestones with some dolomites; 3 K1,2—Cretaceous limestone with layers of bituminous dolomite, limestone and dolomite breccias on Snežnik Mountain, K1—limestones and partly dolomites; 4 J3 1;2 and J3 2;3 —Jurassic limestone; 5 J2— Jurassic dark grey dolomite in alteration with grey limestone; 6 T3 2 þ 3 —Upper Triassic dolomite

To make the longitudinal geological profile A–B–C–D, morphology was taken from the 1:50,000 morphological map. Lithological and tectonic data were taken from more sources as the Basic geological map Postojna (Buser et al. 1967)

and Ilirska Bistrica (Šikić et al. 1972), from the structural– geological map of Čar and Gospodarič (1984) and from the tectonic map of Poljak (2000). Elevation of cross section of the Rak water channel at Planina Cave was added according to

4

M. Blatnik et al.

A

B

C

D

Fig. 1.2 Longitudinal geological profile A–D (A Malni, B Poček, C Mašun, D Snežnik). Legend 1 Malni spring; 2 cross section of the Rak channel in Planina Cave; 3 thrust fault; 4 a fault with possible continuation; 5 vertical movement along a fault; 6a limestone; 6b dolomite; 7 K2 2;3 —Cretaceous limestone with rudists and thinner dolomite layers; 8 1 K2 2 and 2 K2 1;2 —Cretaceous limestones with some dolomites; 9 K1,2—Cretaceous limestone with layers of bituminous

dolomite, limestone and dolomite breccias on Snežnik; K1—limestones and partly dolomites; 10 J3 1;2 and J3 2;3 —Jurassic limestone; 11 J2— Jurassic dark grey dolomite in alteration with grey limestone; 12 T3 2 þ 3 —Upper Triassic dolomite. Longitudinal cross section modified by S. Šebela after Buser et al. (1967), Čar and Gospodarič (1984), Poljak (2000), Šikić et al. (1972). Profile heights are not in the same scale as the profile length

speleological data. Direction of fault movements was determined regarding the position of stratigraphic units and the dip angle of bedding. We see that some extent already existing geological maps with some additional self-made longitudinal sections can help in specific karst-related studies.

A result of detailed structural–lithological mapping of karst caves is a very precise structural–geological map. An example of such map is presented in Fig. 1.4. This is a hand-drawn map from 1994 of the part of Postojna Cave. We can see that there are numerous fissures that are combined to zones. When we put fractured zones on the cave map, we are able to get the image of different directions of the fractured zones and connections between them (in the sense which fractured zone is cut by another zone). With studies of 93 cross sections in Postojna Cave (Šebela 1998), it was determined that 37.6% of cross sections are shaped according to bedding. It was shown that selected cave passages are formed along bedding planes (Fig. 1.3e), moved bedding planes and connective fissures. The advantage for speleogenesis of some bedding planes and moved bedding planes is represented with their connection into penetrative effective porosity in specific structural block (Čar and Šebela 1998). In the same period as geological mapping of the cave, structural geological mapping of the surface directly above Postojna Cave was accomplished (Šebela 1998, 2012). Principal fault zones on the surface were connected with fault zones mapped in cave passages. If we add LiDAR map on geology and cave ground plan, we get a clear detailed morphological and structural–geological map of the area above Postojna Cave (Fig. 1.5).

1.1.2 Detailed Structural–Geological Mapping of the Postojna Cave Area The area of Postojna Cave (cave and surface) was first mapped by Gospodarič (1965, 1976). Besides lithology, he studied fault planes and fissures in the cave which were not described as zones. The new tectonic–lithological mapping of Postojna Cave was done in the scale 1:500 (Šebela 1998). For the development of cave passages, importance of interbedded movements (flexural slip) which represent secondary deformations of the Postojna anticline with axis orientation NW–SE was specially stressed (Šebela 1998, 2012). Duplex in Postojna Cave (Fig. 1.3a) is attributed to the period of overthrusting of the Upper Cretaceous limestones over Eocene flysch rocks. This was the same period that caused the vergence of the Postojna anticline axis towards SW for 7°–14° (Šebela 1998).

1

Structural–Geological Mapping of Karst Areas

5

Fig. 1.3 Geological structures in Postojna Cave. Legend a Duplex due to overthrusting in Stara Jama, b fault plane is building a cave wall in the passage Rov brez imena, c entrance to Pivka Jama is developed along fault zone, d fault plane with low angle dip in Pisani rov collapse room, e underground Pivka River channel follows direction of bedding planes visible on the cave ceiling

According to the Basic geological map (Buser et al. 1967), the limestones which make up the Postojna Cave as well as the surface above may be attributed to the Upper Cretaceous, i.e. the Turonian and Senonian K2 2;3 and Cenomanian K2 1 age. Chondrodonta lumachelle horizon may be observed in a road cutting between Risovec blind valley and the cave Pivka Jama. The horizon is attributed to the Upper Cenomanian by Rižnar
(1997). In Fig. 1.5, we left this horizon inside Turonian K2 2 . Čar (2018) divided K2 3 horizon into K2 3 and K2 3;4 . In Fig. 1.5, we did not divide Senonian K2 3 horizon. Regarding recent field observations, Maastrichtian (the most upper part of the Upper Cretaceous) carbonate rocks are present in the area of Postojna karst (Otoničar, pers. comm. 2019). To understand dependance between formation of karst surface and underground features on structural–geological features, generations and type of regional tectonic activity must be included. Within the area between Postojna, Planina and Cerknica, Čar and Gospodarič (1984) determined generations of fault zones and the structural geometry of the Snežnik thrust sheet between the Idrija and Predjama faults. They established four generations of deformations from the Neogene and supposedly the Quaternary. The tectonic conditions of the treated terrain are divided into • older movements, • thrust structures and folds, and • fault deformations.

At the end of the Eocene or in the Oligocene, the Alpine– Dinaric region was subjected to intense overthrusting. The beds were first folded and subsequently were broken. During the Miocene and Pliocene, the overthrusting was accompanied by folding (Placer 1982). The faults of the first generation trending NE–SW were active in all the tectonic movements, probably even up to the Holocene. The influence is thought to be present also in collapse dolines around Vodni dol and in those around the blind valley Risovec, as well as in the orientation of the water channels in Črna Jama and Pivka Jama caves. In all these cases, we deal with active water channels which are perpendicular to the folded beds (Čar and Gospodarič 1984). The Predjama Fault (Fig. 1.5) is steep NW–SE trending fault which is one of the most significant regional faults and runs along the NE part of the Pivka basin, passes Postojna and proceeds to the SE (Placer 1981). Wider Predjama Fault zone passes Postojna Cave where tectonic micro-displacements are continuously measured since 2004 by TM 71 extensometers (Šebela et al. 2010). In the period 2004–2018, we detected 0.07 mm of dextral horizontal and vertical movement (in the sense of normal fault) along Dinaric oriented (NW–SE) fault zone in Velika Gora collapse chamber. This shows that some tectonic zones in Postojna Cave belonging to wider Predjama Fault zone (Fig. 1.5) are still tectonically active (Šebela 2008; Sasowsky et al. 2003).

6

M. Blatnik et al.

Fig. 1.4 Detailed structural–geological map of Kristalni Rov in Postojna Cave. Legend a crushed zone, b broken zone, c fissured zone, d Upper Cretaceous limestone, e dip direction and dip angle of bedding planes. Geology mapped and drawn by Šebela in 1994

1.1.3 Folding Deformations and Caves It is obvious that many cave passages formed accordingly to regional structural geology. Detailed tectonic–lithological mapping in the scale 1:1,000 of the three big cave systems in SW Slovenia (Postojna Cave system, Predjama Cave and Škocjan Caves) showed connections between bedding planes and development of cave passages. Cave passages of the Postojna Cave are developed on both flanks of the Postojna anticline. Syncline axis is expressed north from Škocjan Caves passages, while in the area of Škocjan Caves we can only see dipping of the syncline axis as gentle folds. Relation between eastern passage of Predjama and Stara Jama caves shows the position of anticline axis (Fig. 1.6). Formation of the Postojna anticline is post- or co-thrusting period of the Upper Cretaceous limestones over Eocene flysch. The same is probably the case in Predjama Cave. Additionally, in Predjama’s western passage there is a

thrust fault where Upper Triassic dolomite is thrusted over Upper Cretaceous limestones. Predjama’s anticline deformation can be related to this even older deformations as well. In the Cave Stara Jama interbedded slips due to folding deformations are well visible and responsible deformation for passage development. Postojna anticline axis is Dinaric oriented (NW–SE), while anticline axis in Predjama is for 55° declined towards north (Fig. 1.6) regarding Postojna anticline. Syncline axis in the area of Škocjan Caves has cross-Dinaric orientation (NE–SW) and can be related to near-faulting deformations (Divača Fault running in the vicinity), because contact between Eocene flysch and Upper Cretaceous and Paleocene limestone is further away as in Postojna and Predjama Caves. In all three caves, some passages are characteristically formed along interbedded slips which developed due to folding. Bedding planes, especially those deformed by

1

Structural–Geological Mapping of Karst Areas

Fig. 1.5 Geological map of the area above Postojna Cave. Legend 1 surface Pivka River, 2 underground Pivka River, 3 anticline, 4 syncline, 5 thrust fault, 6a fault dip direction and dip angle, 6b supposed fault dip direction and dip angle, 7 overturned beds, 8 Eocene flysch rocks, 9 limestone breccia and conglomerate (Pc2, E1), 10 Upper Cretaceous limestone–Senonian
K2 3 after division by Čar (2018), 11 Upper Cretaceous
limestone–Turonian K2 2 , 12 upper Cretaceous limestone–
Cenomanian K2 1

7

8

M. Blatnik et al.

Fig. 1.6 Ground plans of a Postojna cave, b Škocjan caves and c Predjama cave with anticline (a and c) and syncline (b) axis

interbedded slips, are one of the most important structural elements inside or along which cave passages developed. Cave passages of studied caves are formed on both flanks of folds. Anticlines resulted due to compression in folding tectonic events and are primarily not related to younger faulting.

1.2

Conclusion

Fundamental knowledge about the karst forms cannot be separated from an understanding of the geological structure. Karst areas can be regarded as a dynamic, spatial, geological–hydrological and speleological-succession systems, which are under the constant influence of ongoing tectonic movements (Čar 2018). Detailed field geological mapping of karst in Slovenia in the last 40 years showed strong connection between geological structure and formation of karst surface and underground features. Cave passages are developed according to geological structural elements such as joints, faults, folds, bedding planes and interbedded slips. In studied caves (Postojna Cave, Predjama and Škocjan Caves), tectonised bedding planes play an important role for cave passages formation. Principal regional folds are Dinaric oriented

(NW–SE) in Postojna and Predjama Caves. Due to folding interbedded slips or flexural slips developed what represented the weaknesses in carbonate massif used by waters to form underground paths–karst caves. Bedding planes especially those deformed by interbedded slips are one of the most important structural elements inside or along which cave passages developed. Cave passages of Postojna Cave and Predjama are formed on both flanks of anticlines. Surface tectonic and karst features are well seen on LiDAR maps, but only this information cannot replace field hard-rock geological mapping. Development of digital tools (as photogrammetry) in karst geology is very applicable (Triantafyllou et al. 2019), but detailed field structural–geological mapping cannot be completely exchanged with some kind of automatic method yet. Basic knowledge of karst geology is still waiting for us in the field.

References Buser S, Grad K, Pleničar M (1967) Basic geological map of SFRJ, sheet Postojna 1:100000. Zvezni geološki zavod, Beograd Čar J (1982) Geologic setting of the Planina Polje ponor area. Acta Carsolog 10:75–105 Čar J (1986) Geological bases of karst surface formation. Acta Carsolog 24–25:31–38

1

Structural–Geological Mapping of Karst Areas

Čar J (2001) Structural bases for shaping of dolines. Acta Carsolog 30 (2):239–256 Čar J (2018) Geostructural mapping of karstified limestones. Geologija 61(2):133–162 Čar J, Gospodarič R (1984) About geology of Karst among Postojna, Planina and Cerknica. Acta Carsolog 12:91–106 Čar J, Šebela S (1997) Structural position of vertical karst objects on Postojnska Gmajna. Acta Carsolog 26(2):295–314 Čar J, Šebela S (1998) Bedding planes, moved bedding planes, connective fissures and horizontal cave passages (examples from Postojnska jama cave). Acta Carsolog 27(2):75–95 Čar J, Šebela S (2001) Karst characteristics of thrust contact limestone-dolomite near Predjama. Acta Carsolog 30(2):141–156 Gospodarič R (1963) Exploring the Postojna cave—the gay coloured tunell. Naše jame 4:9–16 Gospodarič R (1964) Traces of the tectonic movements in the glacial period in the Postojna cave. Naše jame 5:5–11 Gospodarič R (1965) Geology of the area between Postojna, Planina and Cerknica. Postojna, unpublished report, p 40 (in Slovene) Gospodarič R (1968) Les stalactites et stalagmites renversées dans la Grotte de Postojna. Naše jame 9:15–31 Gospodarič R (1969a) Les processus spéléologiques du pleistocene supérieur dans la Grotte de Postojna. Naše jame 10:37–46 Gospodarič R (1969b) Probleme der Bruchtektonik der NW Dinariden. Geol Rundschau 59(1):308–322 Gospodarič R (1976) Razvoj jam med Pivško kotlino in Planinskim poljem v kvartarju (summary The quaternary caves development between the Pivka basin and Polje of Planina). Acta Carsolog 7:8– 135 Janež J (1997) Hydrogeology. Karst hydrogeological investigations in south-western Slovenia, 7th SWT. Acta Carsolog 26(1):73–86 Janež J, Čar J (1997) Geologic conditions and some hydrogeologic characteristics of the Vipava springs. Karst Hydrogeological investigations in south-western Slovenia, 7th SWT. Acta Carsolog 26(1):86–91 Jurkovšek B, Toman M, Ogorelec B, Šribar L, Drobne K, Poljak M (1996) Formacijska geološka karta 1:50.000 južnega dela Tržaško-Komenske planote (Geological map of the southern part of the Trieste—Komen plateau 1:50,000). Cretaceous and Palaeogene carbonate rocks. Inštitut za geologijo, geotehniko in geofiziko, Ljubljana, p 143 Knez M (1996) Vpliv lezik na razvoj kraških jam. Primer Velike doline, Škocjanske jame (summary The bedding-plane impact on development of karst caves. An example of Velika dolina, Škocjanske jame caves). Zbirka ZRC 14, Ljubljana, p 186 Kogovšek J, Knez M, Mihevc A, Petrič M, Slabe T, Šebela S (1999) Military training area in Kras (Slovenia). Environ Geol 38(1):69–76 Mahmud K, Mariethoz G, Baker A, Treble PC, Markowska M, McGuire E (2016) Estimation of deep infiltration in unsaturated limestone environments using cave lidar and drip count data. Hydrol Earth Syst Sci 20:359–373 Palmer AN (2007) Cave geology. Cave Books, Dayton, Ohio, p 454 Petrič M, Kogovšek J, Ravbar N (2018) Effects of the vadose zone on groundwater flow and solute transport characteristics in mountainous karst aquifers—the case of the Javorniki-Snežnik massif (SW Slovenia). Acta Carsolog 47(1):35–51 Placer L (1981) Geološka zgradba jugozahodne Slovenije = Geologic structure of southwestern Slovenia. Geologija 24(1):27–60 Placer L (1982) Structural history of the Idrija mercury deposit. Geologija 25(1):7–94 Placer L (1996) On the structure of Sovič above Postojna. Geologija 37–38(1994–1995):551–560

9 Placer L, Vrabec M, Celarc B (2010) The bases for understanding of the NW Dinarides and Istria Peninsula tectonics. Geologija 53 (1):55–86 Pleničar M (1960) The stratigraphic development of cretaceous beds in Southern Primorska (Slovene Littoral) and Notranjska (Inner Carniola). Geologija 6:22–145 Pleničar M (1961) Beitrag zur Geologie des Höhlensystems von Postojna. Naše jame 1–2(1960):54–58 Pleničar M (1970) Basic geological map of SFRJ 1:100,000. Geology of the Postojna Sheet. Zvezni geološki zavod, Beograd, p 62 Poljak M (2000) Strukturno-tektonska karta Slovenije 1:250,000. Mladinska knjiga tiskarna d.d, Ljubljana Rižnar I (1997) Geologija okolice Postojne. Magistrsko delo, Univerza v Ljubljani, Naravoslovnotehniška fakulteta, Oddelek za geologijo, Ljubljana, p 78 Sasowsky ID, Šebela S, Harbert W (2003) Current tectonism and aquifer evolution >100,000 years recorded in cave sediments, Dinaric karst, Slovenia. Environ Geol 44(8):8–13 Silva OL, Bezerra FHR, Maia RP, Cazarin CL (2017) Karst landforms revealed at various scales using LiDAR and UAV in semi-arid Brazil: consideration on karstification processes and methodological constraints. Geomorphology 295:611–630 Šebela S (1992) Geological characteristics of Pisani rov in Postojna cave. Acta Carsolog 21:97–116 Šebela S (1996) The influence of tectonic zones on cross section formations in the Predjama cave, Slovenia. Kras i speleologia 8:72– 77 Šebela S (1998) Tectonic structure of Postojnska jama cave system. ZRC Publishing 18, Ljubljana, p 112 Šebela S (2008) Broken speleothems as indicators of tectonic movements. Acta Carsolog 37(1):51–62 Šebela S (2009) Structural geology of the Škocjan Caves (Slovenia). Acta Carsolog 38(2–3):165–177 Šebela S (2012) Postojna-Planina cave system, Slovenia. In: White WB, Culver DC (eds) Encyclopedia of caves, 2nd edn. Academic Press, Amsterdam, pp 618–624 Šebela S, Čar J (1991) Geological setting of collapse chambers in Vzhodni rov in Predjama cave. Acta Carsolog 20:205–222 Šebela S, Čar J (2000) Velika Jeršanova doline—a former collapse doline. Acta Carsolog 29(2):201–212 Šebela S, Vaupotič J, Košt’ák B, Stemberk J (2010) Direct measurement of present-day tectonic movement and associated radon flux in Postojna cave, Slovenia. J Caves Karst Stud 72(1):21–34 Šikić D, Pleničar M (1975) Tumač za list Ilirska Bistrica, Osnovna geološka karta 1:100000. Savezni geološki zavod, Beograd, p 50 Šikić D, Pleničar M, Šparica M (1972) Osnovna geološka karta SFRJ, list Ilirska Bistrica 1:100000. Savezni geološki zavod, Beograd Šušteršič F (2006) Relationships between deflector faults, collapse dolines and collector channel formation: some examples from Slovenia. Int J Speleol 35:1–12 Šušteršič F, Čar J, Šebela S (2001) Collector channels and deflector faults. Naše jame 43:8–22 Triantafyllou A, Watlet A, Le Mouélic S, Camelbeeck T, Civet F, Kaufmann O, Quinif Y, Vandycke S (2019) 3-D digital outcrop model for analysis of brittle deformation and lithological mapping (Lorette cave, Belgium). J Struct Geol 120:55–66 Zlot R, Bosse M (2014) Three-dimensional mobile mapping of caves. J Cave Karst Stud 76:191–206 Žvab Rožič P, Čar J, Rožič B (2015) Geological structure of the Divača area and its influence on the speleogenesis and hydrology of Kačna Jama. Acta Carsolog 44(2):153–168

2

Late Cretaceous and Paleogene Paleokarsts of the Northern Sector of the Adriatic Carbonate Platform Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna In Western Slovenia, a paleokarstic surface with clayey bauxite deposits separates late? Cenomanian to late Turonian strata from middle/late Coniacian palustrine?, peritidal and shallow-marine carbonate deposits along the external-most preserved parts of the Adriatic Carbonate Platform (AdCP). In southwestern Slovenia and Istria (SW Slovenia and NW Croatia), an even more pronounced paleokarstic surface characterised by bauxite deposits separates the Valanginian/ Hauterivian to Campanian shallow-marine carbonates of the inner parts of the AdCP from the late Campanian?/Maastrichtian to Eocene palustrine, peritidal and shallow-marine carbonates of the synorogenic carbonate platform. Because of the asynchronous character of the stratigraphic gaps and their apparent temporal and partially also spatial continuity, Korbar (pers. comm.) proposed that both paleokarsts may have formed during one and the same paleokarstic period as a result of the same geotectonic event. It was further proposed that during the Late Cretaceous these two areas were separated by a deeper marine interplatform basin (i.e. the NE Adriatic trough as a northern continuation of the Budva Basin) (Korbar 2009) which split the northern sector of the Adriatic-Dinaridic carbonate platform (s. lato) into the Adriatic and Dinaridic carbonate platforms (s. stricto) (Korbar 2009) and also interrupted the uniformity of the paleokarst. This work aims to show that during the Late Cretaceous two spatially and temporally separated paleokarstic periods M. Blatnik
F. Gabrovšek
M. Knez (&)
B. Kogovšek
J. Kogovšek
C. Mayaud
A. Mihevc
J. Mulec
M. Năpăruş-Aljančič
B. Otoničar
M. Petrič
T. Pipan
M. Prelovšek
N. Ravbar
T. Shaw
T. Slabe
S. Šebela
N. Zupan Hajna Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia e-mail: [email protected] D. C. Culver American University, Washington, DC, USA H. Liu Yunnan University, Kunming, China

occurred in the northern sector of the AdCP which were not in a direct causal relationship. Moreover, we will also show that in the area where both paleokarsts pinched out (i.e. wider Postojna region) or were not developed, no evidence for a deep-marine interplatfrom basin occurs. Since carbonate platforms are predominantly very shallow-marine depositional systems, not only large, but also a considerably small, relative sea-level falls can expose them to terrestrial conditions and hence karstification. The nature of subaerial exposures with the general geological and depositional evolution of the investigated and adjacent areas, as well as events at plate boundaries and the eustatic sea-level changes, hide the causes for the occurrence of a particular paleokarst. In this chapter, we will follow the classification of Osborne (2000) which defines paleokarst as karst developed largely or entirely during past karst periods, i.e. long-lasting times of continental weathering and groundwater circulation, which was terminated by an ensuing marine transgression over the karstic surface (Bosák et al. 1989). This classification is also in accordance with the general definition of the karst (see Klimchouk and Ford 2000), from which follows that a karst (hydrological) system passes into a paleokarst when its mass transport function has been lost. Thus, from a hydrogeological point of view, a karst aquifer becomes paleokarst when it stops transporting aggressive water and becomes isolated from an active karst system. In this respect a paleokarst does not imply any particular type of a karst but rather refers to a condition, namely a karst as a system that has become fossilized. Carbonate platforms are depositional systems where most of the world’s carbonate sediments/rocks have been deposited. Similarly, as the plate tectonics determines the development of depositional carbonate successions (see Bosellini 1989), bauxite (see D’Argenio and Mindszenty 1995) and karst occurrences among others also depend on the geodynamic evolution and distance of an area from lithospheric plate boundaries. Thus, carbonate platforms may experience

© Springer Nature Switzerland AG 2020 M. Knez et al. (eds.), Karstology in the Classical Karst, Advances in Karst Science, https://doi.org/10.1007/978-3-030-26827-5_2

11

12

M. Blatnik et al.

an entire geodynamic spectrum of the Wilson cycle during their lifetimes. Each stage of the Wilson cycle yields its own tectonic characteristics that influence not only the depositional history of a certain carbonate platform but also its diagenetic history, constructive and destructive. Carbonate platforms in terms of active sediment systems cease to grow as active sediment systems when they become exposed to conditions where significant production of carbonates is prevented. Such conditions are achieved, among others, if a carbonate platform is exposed to a land, and a relative sea-level fall may be the result of eustatic or/and tectonic processes. So, the platform may be subjected to aggressive waters that cause dissolution or karstification of different extent and duration. At the end, the carbonate platform may literally die away, frequently from the uplift or drowning of substantial parts of the platform due to orogenic processes. Thus, the development of a particular type of karstification is to a great extent a function of the position of the carbonate platform relative to its geotectonic position.

2.1

Geological Setting

During the Mesozoic carbonate platforms that thrived in the area of today’s Slovenia were located in dynamic geotectonic realms, greatly influenced by events at the lithospheric plate boundaries in the area close to the various ocean bays of the western Tethys. The passive continental margins of the adjacent continental plates and microplates were prone to extensive colonization by carbonate platforms, which were only occasionally interrupted by the sedimentation of terrigenous clastics. Tectonically-influenced deviations from the expected arrangement of depositional sequences at passive continental margins are often associated with geotectonic events at more or less distant active lithospheric plate boundaries, particularly during their rearrangement. During the Mesozoic, carbonate platforms located in the area of today’s Slovenia witnessed to all phases of the geodynamic spectrum of the Wilson cycle. To a great extent the geological characteristics of Slovenia result from its geotectonic position between the African and Eurasian plates and the intermediate Adriatic-Apulian microplate (AAMP) (sensu Stampfli et al. 1998). Currently, three major geotectonic units meet here—the Alps, the Dinarides and the Pannonian basin, which with their specific geological evolution also resulting in somehow different character and abundance of carbonate rocks and related karst. In Slovenia, a majority of karst terrains are located in the Dinarides and Southern Calcareous Alps in the western half of Slovenia (Fig. 2.1). In the Dinarides, carbonate rocks occupy mainly western and southwestern part of Slovenia or a fold-and-thrust belt of the External Dinarides, while in the Southern Calcareous Alps form a major part of the Julian

Alps, Kamnik-Savinja Alps and Karavanke Mountains or its S- to SE-verging fold-and-thrust belt (Fig. 2.1). Mountainous karstic regions of the Dinarides and Southern Calcareous Alps and their foothills are separated from the Central Alps (i.e. the Eastern Alps) by the pronounced Periadriatic fault (Fig. 2.1), while towards the west and east they sink below the Tertiary and Quaternary deposits of the Po and Pannonian Basins and the Adriatic Sea. Recently, in a geotectonic sense, the area of the western half of Slovenia belongs to the Dinaric-Hellenic plate, while autochthonous Istria (in terms of Placer 1998) belongs to the Adria or the Adriatic-Apulian microplate (AAMP), respectively. For most of the Mesozoic Period the region between Eurasia and Gondwana, or the western part of the ‘Great Tethys Bay’ of Pangea, was occupied by a more or less uniform AAMP, the size and shape of which have been changing accordingly to the main geotectonic events throughout the geologic history. In the northeastern part of the AAMP, a more or less uniform and isolated Adriatic Carbonate Platform (AdCP) (see below), surrounded by deep-marine interplatform and oceanic basins, was formed after Middle Triassic and Triassic/Jurassic extensional tectonic phases. According to the tectonic regionalization of Placer (1998), the study area in western Slovenia consists of the External Dinarides and the Dinaric Foreland (Fig. 2.1). A nappe structure in the northwestern part of the External Dinarides contains five successively lower and younger thrust units. From northeast to southwest these follow the Trnovo Nappe, Hrušica Nappe, Snežnik Thrust Sheet, Komen Thrust Sheet and Kras Thrust Edge (Placer 1981, 1998, 2004) (Fig. 2.1). The External Dinarides and the Dinaric foreland correspond to the northwestern part of the Cretaceous Adriatic Carbonate Platform and the Upper Cretaceous-Eocene synorogenic carbonate platform which occupied the northeastern part of the AAMP. In the Cretaceous, the area of the present-day Southern Alps was a part of the deeper marine realm which comprised the Slovenian Basin (Cousin 1981; Buser 1989) and the area of former Julian Carbonate Platform (Cousin 1981; Buser 1989) (see above). The geologic and paleogeographic situation started to change dramatically in the Late Cretaceous (see below). Due to a general compressional tectonic regime or to tectonic activities at plate boundaries, a few regional paleokarstic periods interrupted a shallow-marine carbonate deposition on the otherwise passive margin of AdCP from the Middle Jurassic until the Late Cretaceous. In the External Dinarides, the Mesozoic shallow-marine deposits of the AdCP are overlain by the Maastrichtian to Eocene shallow to gradually deeper marine limestone of the synorogenic carbonate platform and prograding hemipelagic marls and deep-water clastics (flysch). At the periphery of the foreland basin, carbonate successions of the AdCP are separated from the

2

Late Cretaceous and Paleogene Paleokarsts …

Fig. 2.1 Geographical position and simplified geological map of the western Slovenia and Istria showing major structural elements (modified from Placer 1998)

13

14

M. Blatnik et al.

overlying deposits of the synorogenic carbonate platform by a paleokarstic unconformity (Otoničar 2007) (see below). In the Slovenian Basin mixed siliciclastic and deeper marine carbonate sediments were deposited during the Mesozoic. Compressional tectonics, related to closures of the nearby small oceanic basins of the western extension of the Neo-Tethys dominated the area from the Middle Jurassic, culminating in forming the foreland basins in the Upper Cretaceous to Eocene and in the final uplift of the Dinaric range during the Oligocene and Miocene.

2.2

Lower Cretaceous Paleokarst

In the SW Slovenia, the significance of paleokarst phenomena and features related to long-lasting subaerial exposure of carbonate deposits above the sea-level for interpreting the depositional evolution of the Lower Cretaceous carbonate successions has been recognized but has yet to be studied in detail. From the northern marginal parts of the AdCP irregular vertical karst fissures filled with eroded upper Albian shallow-marine and pelagic carbonates, as well as horizontal cave systems with cross-bedded pelagic wackestones have been reported (Grötsch 1994). In the central part of the northern sector of the AdCP (Kras Plateau) up to one metre thick lower Albian emersion breccia occurs at the base of the Povir Formation (Jurkovšek et al. 1996). This breccia is thought to be a part of a wider emersion horizon found throughout the AdCP as the boundary between two large-scale sequences (Tišljar and Velić 1991; Velić et al. 2003). In Istria, the horizon of breccia-conglomerate with a clay matrix overlies a hummocky karren-dominated paleokarstic surface that alternates with the illitic greenish clay with pyrite that fills up to almost a metre deep paleokarstic pits (Durn et al. 2003). The host rock of the paleokarst is composed of several different lithofacies and stratigraphic levels (from the late Barremian to late Aptian) that systematically vary over relatively short distances. In contrast, the upper Albian transgression over the paleokarstic surface was relatively synchronous (Velić et al. 1989). As mentioned above, from the Middle Jurassic onwards, the northern sector of the AdCP was generally under a compressional tectonic regime. The area of today’s Istria (former inner part of the Cretaceous AdCP) was somehow more prone to positive plicative deformations than other areas of the northern sector of the AdCP. They are reflecting in thin sequences of shallow-marine peritidal lithofacies with frequent evidence for inter- and supratidal environments and occasional prolonged emersion periods. Directions of depositional trends towards open marine environments and above all frequent occurrence of dinosaur footprints and also bones from the latest Jurassic through the whole Early Cretaceous indicate more or less permanently present vast

land area in the vicinity (i.e. west from the current western coastline of Istria) (Otoničar 2007). Very shallow peritidal environments extending over areas of the northern sector of the AdCP were most probably or at least in part the result of the Valanginian global eustatic long-term sea-level low-stand, the most pronounced low-stand in the whole Cretaceous (see Haq 2014). However, due to local occurrences of deepened intraplatform lagoons/basins (Orehek and Ogorelec 1976), geotectonic events reported from the Northern Calcareous Alps (Late Jurassic/Early Cretaceous obduction and subsequent major deformations accompanied by the stacking of the Austroalpine nappe units and related formation of the synorogenic Rossfeld sedimentary basin) commenced in the Late Valanginian (ca. 135 Ma) (Faupl and Wagreich 2000; Schmid et al. 2008) and especially processes related to the obduction of Western Vardar Ophiolitic Unit onto Adriatic passive margin east from the Bosnian–Bled Basin in the Late Jurassic and Early Cretaceous (see Schmid et al. 2008; Goričan et al. 2018) could also have a significant impact on a depositional and wider geological evolution of the AdCP. During certain periods (e.g. Aptian-Albian subaerial exposure event) however, much broader areas were subaerially exposed and subjected to karstification and/or pedogenesis. Despite the documented latest Aptian (i.e. 113.3 Ma—KAp7) major eustatic sea-level fall which coincides also with the minimum of the long-term sea-level curve (Haq 2014) this event most probably pre-dates the Albian paleokarst discussed above. It seems even less plausible that the paleokarst would be related only to one (or amalgamated) of the lower Albian eustatic sea-level falls (e.g. KAl1-4; sensu Haq 2014) while the KAp7 fall would not have been observed in the sedimentary record. Due to these arguments, as well as the asynchronous gap, fissure guided karstic shafts at the northern margin of the platform (see above) and accelerated deposition of breccia at Aptian/Albian boundary in the Slovenian basin (Cousin 1981) we suggest that intensification of tectonic processes lead to an asynchronous uplift and subaerial erosion of certain parts of the platform. This accelerated tectonic activity coincided with the late Aptian to Albian onset of subduction of the Alpine Tethys and in a wider sense also to the late Barremian to Aptian ‘Austrian’ phase of orogeny when the Eastern Vardar Ophiolitic Unit overrode the internal or western margin of the Dacia Mega-Unit (Schmid et al. 2008).

2.3

Cenomanian to Late Coniacian/Early Santonian Paleokarst

In western Slovenia up to 1200 m thick Albian to Campanian carbonate succession of the northern and northeastern outermost preserved parts of the northern sector of the AdCP

2

Late Cretaceous and Paleogene Paleokarsts …

15

Fig. 2.2 Chronostratigraphic correlation of upper Cretaceous lithostratigraphic units of the northern part of the Adriatic carbonate platform. The Hrušica site (Matarsko Podolje area) represents the innermost part of the platform while other sites represent the more marginal parts. Note significant difference in extension and stratigraphic position of the stratigraphic gap that occurs between these areas (modified from Jež and Otoničar 2018)

has been divided into eight lithostratigraphic units (Jež and Otoničar 2018) (Fig. 2.2). Temporally and spatially, shallow-marine lagoonal and peritidal facies of the inner platform/ramp alternate with deeper marine hemipelagic facies of the intraplatform basins. This otherwise rather continuous succession is interrupted by a pronounced stratigraphic gap (Fig. 2.2) characterized by a paleokarstic surface (Fig. 2.3a).

2.3.1 Paleokarstic Features Karstic phenomena include mainly vadose subcutaneous cavities such as vugs, pockets and widened root channels (i.e. rhizolites) filled with reddish-stained fine-grained carbonate sediments, karst breccia, yellowish- to reddish-stained oolitic clayey bauxite, speleothems (i.e. flowstone, calcite rafts…) and calcite spar cements (Figs. 2.3 and 2.4). Paleokarstic features penetrate up to 10 m below the paleokarstic surface. Locally, the paleokarstic surface is marked by lenses of oolitic clayey bauxite (boehmite, kaolinite, anatase) up to 50 cm thick. In some locations, the paleokarstic surface has been recognized only on a basis of low values of oxygen and, in particular, carbon isotopes of the bulk limestone that directly underlain it (Otoničar and Jež 2012).

2.3.2 Paleokarst Stratigraphy The paleokarstic surface separates different parts of the Turonian (unit 5) from the Coniacian/Santonian sequences (unit 6) with one exception, the platform’s outermost section among the investigated sites, Mt. Sabotin, where the paleokarstic surface is developed on the Middle Cenomanian limestone (unit 3) (Jež and Otoničar 2018) (Fig. 2.2). There are reports from other places along the NE margin of the AdCP (NW Bosnia and Hercegovina) where paleokarstic relief characterized by bauxite deposits separates Middle Cenomanian or even Upper Albian strata from Upper Santonian limestone (Dragičević and Velić 2002; Galić et al. 2015). However, according to current biostratigraphic interpretations (Frijia et al. 2015) the immediately overlying strata could also be considered as Coniacian or at most Lower Santonian in age (Jež and Otoničar 2018). While the discussed paleokarst occupied more outer parts of the mid-Cretaceous AdCP, in the inner parts of the platform even deeper marine intraplatform basins or deep lagoons occurred contemporaneously (see Jurkovšek et al. 1996) (Fig. 2.5). However, from the other side, the late Turonian age of the significantly pedogenically modified horizon that occurs in some carbonate successions in the inner areas of the platform (e.g. Matarsko Podolje and Mt. Slavnik) (Otoničar 2006;

16

M. Blatnik et al.

Fig. 2.3 Paleokarst related phenomena of Hrušica Plateau. Legend a Turonian and Upper Coniacian/Lower Santonian limestones are separated by a distinctive paleokarstic surface marked by bauxitic deposits (Podkraj, Hrušica Plateau). Note paleo-epikarstic zone criss-crossed by infilled irregular channels (root related?); b vadose

channel filled with sandy-grained clayey bauxitic material (Nadrt, Hrušica Plateau); c clayey oolitic bauxite (boehmite-kaolinite) with reddish dark brown hematite in intergranular pores (Nadrt, Hrušica Plateau)

Fig. 2.4 a Intercalation of reddish-stained micrite and coarse-grained calcite cements (rafts) representing a filled primarily phreatic paleokarstic passage (Kališe); b dissolution void in biopeloidal G/P a few

metres below the paleokarst surface filled by bladed meteoric calcite spar crust and silty calcareous material (Kališe); c recrystalized calcite rafts with dissolution void filled with calcite spar

Jež et al. 2011) may indicate the maximum extent of the subaerially exposed area (see Jež and Otoničar 2018). However, the continuous shallow-marine sedimentation seen in the complete Turonian succession at Postojna (Šribar 1995;

Rižnar 1997; Uršič Arko and Otoničar 2019) which is located between these two regions, or even closer to the area with the paleokarst, indicates that the land surface was not continuous over the platform interior during this late Turonian event.

2

Late Cretaceous and Paleogene Paleokarsts …

17

Fig. 2.5 Paleogeographic evolution of the northern sector of the Adriatic carbonate platform between Albian and Maastrichtian presented on cross-section over the northern part of the platform between Istria (SW) and Sabotin (NE) (modified from Jež and Otoničar 2018)

Thus, this stratigraphic gap or type 1 sequence boundary (sensu Schlager 1999) considerably increases from inner towards northern and northeastern marginal parts of the northern sector of the AdCP. While the age of the immediate footwall generally increases in the same direction, the age of the immediate hanging-wall is much more uniform and mainly marked by foraminifera Murgella lata or its biozone (Jež and Otoničar 2018). Although NE marginal-most parts of the northern sector of the AdCP are not preserved, it is evident (see above) that the extent of the paleokarst related stratigraphic gap decreases from the marginal towards the inner parts of the platform where it gradually diminished and at some line passed over to a depositional conformity (e.g. Postojna area) (Fig. 2.5) (Uršič Arko and Otoničar 2019).

2.3.3 Discussion The possibility that in our case the subaerial exposure was induced entirely by distinctive Late Turonian 3rd order,

eustatic sea-level fall (Haq et al. 1987; Haq 2014) does not seem probable because in such a scenario it would be expected that a more uniform stratigraphic gap would spread over a much larger part of the platform. Also, an empty bucket model (sensu Schlager 1981) where growth of the marginal parts substantially overpasses the sedimentation rate in the inner parts of the platform—in our case supposedly triggered by the Cenomanian/Turonian long-term eustatic sea-level rise and subsequent the Late Turonian eustatic 3rd order sea-level fall—does not explain real situation (see Jež and Otoničar 2018 and discussion therein). If this would be the case, the stratigraphic gap at the outer parts of the platform would be more uniform and the age of the immediate footwall would not be older than Turonian regardless the location, as the topography would be entirely the result of the Turonian accretion of the outer parts of the platform (Jež and Otoničar 2018). Moreover, the re-established shallow-marine peritidal depositional environments of unit 5, after the Cenomanian/

18

Turonian sea-level rise what was previously interpreted as the result of the Late Turonian 3rd order eustatic sea-level fall (see Gušić and Jelaska 1990, 1993; Jurkovšek et al. 1996, 2013) had already occurred in the early Turonian (Jež and Otoničar 2018) (Fig. 2.2). In the inner part of the platform a distinctive horizon of pedogenically modified limestone defined as a type 2 sequence boundary occurs at the Matarsko Podolje and Mt. Slavnik (Otoničar 2006; Jež et al. 2011; Jež and Otoničar 2018) (see above) and may represent the Late Turonian 3rd order eustatic sea-level fall. Thus, the extent of the platform exposed to the land surface increased during the Late Turonian event but evidently, some parts of the platform interior (e.g. the former intraplatform basin or deep lagoon) still remained inundated (see above and Jež and Otoničar 2018). In the Postojna area, less than 10 km towards the interior of the platform from the innermost documented paleokarst, characterized by clayey bauxite on Mt. Nanos (considering palinspastic; see Placer 1981), no signs of paleokarst or of a paleosol horizon have been found in the Turonian and Coniacian carbonate successions. However, a regression that culminated in a 15-m thick horizon with significant fenestrae which is roughly contemporaneous with the above mentioned paleosol horizon was documented (see Uršič Arko and Otoničar 2019). A levelled relief and relatively unified ages of the immediate hanging-wall deposits in comparison with the immediate footwall ages indicate slow continuous tectonic uplift of the platform’s marginal parts that had been prograding towards platform interior from at least the Late Cenomanian until the Middle Coniacian (maximal extent) (Jež and Otoničar 2018). Because the paleokarstic features do not penetrate very deep below the surface, the rate of the relative uplift should have gone more or less hand in hand with the denudation rate or some significant periods of tectonic quiescence during the general relative lifting of the area when the subaerially exposed topography was levelled should have occurred (Jež and Otoničar 2018). It is highly possible also that the documented partial incipient drowning of the internal parts of the platform at the Cenomanian/Turonian boundary, which largely coincides with the uplift of the external parts, is not entirely the result of long-term eustatic sea-level rise and related phenomena but also, as proposed for the marginal uplift, is a result of compressional intra-plate horizontal stresses induced by distant collision related processes that may produce both, broadscale positive and negative lithospheric deflections (Ziegler et al. 1995). Other Turonian deeper marine events in the inner parts of the platform could also be explained in a similar matter. In our case, the uplift of the study area coincides with the

M. Blatnik et al.

NW-ward thrusting in the Dacia and Tisza Mega-Units which locally affected early Turonian sediments and pre-dated the latest Turonian onset of deposition of the post-tectonic Late Cretaceous Gosau sediments (see Schmid et al. 2008). The same authors also tentatively assigned the basal thrust of the Drina-Ivanjica thrust sheet (Inner Dinarides) to the early Late Cretaceous (100–85 Ma, Late Albian-Coniacian) compressional event which confirms accelerated compressional tectonic activity not only in the areas adjacent to AdCP but also in the AdCP itself. It should be noted also that in the Turonian large parts of the highly deformed adjacent Austroalpine domain had been elevated above the sea-level during the climax of the Eoapline orogeny (Faupl and Wagreich 2000). In addition, dinosaurian footprints found in the Late Cenomanian (Dalla Vecchia 1998, 2001) and Late Turonian to Coniacian (Mauko and Florjančič 2003) peritidal carbonate successions along the western and southeastern coast of Istria indicate larger emerged area west of today’s Istria (Matičec et al. 1996; Otoničar 2007) or another positive deflection at the northern sector of the AdCP during the period of discussion (Jež and Otoničar 2018).

2.3.3.1 Depositional Evolution of the Northern Sector of the AdCP Between the Coniacian and Maastrichtian (or Between the Described Major Paleokarstic Periods) After the post-lower Coniacian transgression a carbonate ramp depositional system oriented towards the inner part of the platform was established over the former subaerially exposed areas in the late Coniacian and Santonian. During the early Campanian, deeper marine inner platform areas were partly filled by prograding calcarenite shoals (Jež and Otoničar 2018). Thus, shallow-marine depositional environments were re-established over a large part of the northern sector of the AdCP although in the central part (Kras Plateau), at least, periodically deeper marine conditions existed throughout the Campanian (Jurkovšek et al. 1996, 2013). In the study area, the more or less continuous deepening of the depositional environments during the post-early Campanian indicates the onset of the progressive drowning of the marginal parts of the platform and the tilting of the platform towards the developing foreland basin (Jež and Otoničar 2018). The drowning of the most marginal parts of the AdCP culminated in the deposition of deeper marine hemipelagic marls and overlying flysch. Simultaneously, the inner parts of the platform were uplifted, subaerially exposed and karstified, while the area between the land and the deep-marine foreland basin was occupied by a synorogenic carbonate ramp depositional system (see below).

2

Late Cretaceous and Paleogene Paleokarsts …

2.4

Late Cretaceous to Paleogene Paleokarst (a Stratigraphy and Evolution of the Forebulge Related Paleokarst)

In southwestern Slovenia and western Croatia (e.g. Istria) a regional unconformity (i.e. an irregular paleokarstic surface, locally marked by bauxite deposits) separates passive margin shallow-marine carbonate successions of different Cretaceous formations from the Upper Cretaceous to Eocene palustrine and shallow-marine limestones (Fig. 2.6). The later correspond to the Kras Group (Košir 2003) (Fig. 2.6), which represents the lower unit of the underfilled peripheral foreland basin stratigraphy (i.e. the lower unit of the ‘underfilled trinity’ of Sinclair 1997). Thus, the unconformity represents a mega sequence boundary and typically separates the underlying passive margin carbonate succession from the overlying deposits of the synorogenic carbonate platform at the periphery of the foreland basin (Košir and Otoničar 2001). The synorogenic carbonate platform was finally buried by prograding hemipelagic marls and deep-water clastics (i.e. flysch) (Fig. 2.6).

2.4.1 Paleokarstic Features In the investigated area pronounced paleokarstic features, both surface and subsurface, were developed in subaerially exposed diagenetically immature eugenetic carbonates. In places, the paleokarstic surface is characterized by surface karst forms, such as karren, dolines (Fig. 2.7a) and depressions of decimetric amplitude (Fig. 2.7b). Epikarst features developed included, pedogenic features and enlarged root related channels (Fig. 2.7c). Vadose channels, shafts and pits penetrate up to a few tens of metres below the paleokarstic

19

surface (Fig. 2.7d), where they may merge with originally horizontally oriented phreatic cavities. The latter shows the characteristics of caves formed in fresh/brackish water lenses (e.g. flank margin caves?) (Fig. 2.8a, b). In extensive outcrops, the remains of these caves can be followed up to a few hundreds of metres along a strike. In one case a breccia body which was later defined as a paleokarstic cave-related deposit (Otoničar et al. 2003), is so extensive that it was mapped as a lithostratigraphic unit in the Basic geologic map of Yugoslavia 1:100,000 (see Magaš 1965). The phreatic caves are usually irregular and elongate in shape. The caves can be up to a few tens of metres long and up to a few metres high (Fig. 2.8a, b). Depending on their locality, the phreatic caves occur in different positions relative to the paleokarstic surface, the lowest one some 75 m below it. Usually, only one distinct paleocave level occurs at each location, however, indistinct levels of spongy porosity and/or irregularly dispersed cavities of different sizes have been noticed locally. The cavities had been subsequently partly remodelled and entirely filled with detrital sediments (Fig. 2.8a, c) and flowstone (Fig. 2.8a, d) in the upper part of the phreatic, epiphreatic and vadose zones. Relatively small phreatic cavities in the lowermost part of the paleokarstic profiles are commonly filled with geopetal laminated mudstone derived from an incomplete dissolution of the host rock overlain by a coarse-grained blocky calcite of a meteoric or mixing meteoric/marine origin (Otoničar 2006). Somewhat larger phreatic caves located shallower below the paleokarstic surface usually have a more complex stratigraphy. Although the lower parts of the caves are still mainly filled with the reddish-stained micritic carbonate sediment (Fig. 2.8a), different types of flowstone, particularly calcite rafts (Fig. 2.8d), become more prominent higher in the cave profiles. Gradually in the upper parts of the

Fig. 2.6 Generalized lithostratigraphic column of the Upper Cretaceous to Eocene carbonate succession in the Kras and Matarsko Podolje regions, SW Slovenia, showing major lithostratigraphic units (after Košir 2003)

20

M. Blatnik et al.

Fig. 2.7 a Paleokarstic doline filled with breccia and bauxite deposits (Koromačno, Istria, NW Croatia). Note the light-grey limestone with reddish-brown silty calcareous karst related deposit in the lower part of the figure. The bauxite is covered by dark-grey bedded palustrine limestone of the Liburnian Formation. b An undulating paleokarstic surface separates the Santonian light-grey shallow-marine thick-bedded

limestone from the Maastrichtian dark-grey palustrine limestone (Kozina, SW Slovenia). c Paleokarstic subcutaneous root related tube filled with the calcareous pedogenically modified deposit. d Excavated paleokarstic cavity (a vadose shaft?) originally filled with bauxite (Minjera, Istria, NW Croatia)

caves, sediments derived from the paleokarstic surface itself prevail over autochthonous deposits. Channels in the epikarst zone are almost entirely filled with a pedogenically modified material derived directly from the paleokarst surface. Regardless of their origin, the cave deposits have often been intensively modified by pedogenic processes while they were exposed at the paleokarstic surface by denudation. Just prior to the marine transgression over the paleokarstic surface some cavities or their parts had been filled with

marine-derived microturbidites or caymanites (Fig. 2.8c) (see Jones 1992 and Osborne 2008). Below the paleokarstic surface d13C and d18O values of the cavities deposits usually exhibit good correlation with a trend consistent with meteoric diagenesis (sensu Lohmann 1988). The vadose channels and voids are also filled with detrital sediments and flowstone, but these usually differ from fillings of the phreatic cavities in having a higher content of noncarbonate material, lower d13C values of carbonate

2

Late Cretaceous and Paleogene Paleokarsts …

21

Fig. 2.8 a Cross-section of the completely filled paleokarstic cave with the ceiling preserved. Note the alternation from micrite to silty sediment and flowstone. b Horizontally oriented cave of irregular shape largely filled with the reddish-stained calcareous mudstone/siltstone (Podgrad, SW Slovenia). The maximal height of the cave is approx. 4 m. The cave deposits are artificially marked by the reddish

transparent colour in the picture. c Cyclic graded calcareous microturbidites fill the paleokarstic cavity. Individual foraminifera indicate marine-derived sediments (i.e. caymanite; sensu Jones 1992) deposited during early phases of the marine transgression. d A pile of cemented calcite rafts or pool shields (Koromačno, Istria, NW Croatia)

material and more distinctive pedogenic modification. Denudation has frequently exposed the filled paleokarstic subsurface cavities on the paleokarstic surface, where they may be identified only by the remains of their fill (Otoničar et al. 2003; Otoničar 2006). Internal cave sediments and flowstones may also occur as grains in deposits (mostly breccias) that fill the subsurface paleokarstic cavities of different generations and overlain the paleokarstic surface. Some cements in breccias exhibit characteristics typical of bio-diagenesis (Otoničar 2006, 2016) which results from the

activity of various microorganisms in the vadose diagenetic zone (Jones and Kahle 1985). In general, the variety of cave filling deposits and the amount of surface derived material decrease with the distance from the paleokarstic surface. The paleokarstic surface and its depressions, as well as subsurface channels and voids, are often covered and filled by bauxite deposits which were locally exploited (Fig. 2.7a, c and d) (see Gabrić et al. 1995). Some limestone lithofacies immediately covering the unconformity are often locally confined, suggesting that the

22

karstic surface had a highly irregular topography before the onset of transgression. In some places, it is clear that the incipient transgression involved a gradual rise of the water table and, eventually, ponds or ‘blue holes’ were formed in karstic depressions (Durn et al. 2003). In places, in the Kras plateau (SW Slovenia and NE Italy) during the ‘blue hole’ stage of the transgression, paleokarstic pits and doline-like depressions were filled by a coarse-grained breccia and micritic limestone with vertebrate remains, mainly dinosaurian and crocodilian bone fragments and teeth (Debeljak et al. 1999, 2002; Dalla Vecchia 2009). Generally, the cover sequence (i.e. the Liburnian Formation of the Maastrichtian and early Paleogene age) is characterized by restricted, marginal marine and palustrine lithofacies commonly with pedogenic modifications (Otoničar 2006). The lithofacies of the lower part of the Liburnian formation shows many features typical of subaerial exposure surfaces, including calcrete, pseudomicrokarst, brecciated horizons and low-amplitude karstic surfaces (Otoničar 2006). In western Istria, where the chronostratigraphic gap is the most extensive, the foraminiferal limestone (see Fig. 2.6) frequently directly overlies the paleokarstic surface (Matičec et al. 1996). Locally, the lowermost subaerial exposure surface of the Liburnian Formation, which has a karstic topography with decimetre relief and a regolith with a kaolinitic matrix, may form a composite unconformity with the main paleokarstic surface (Otoničar 2006).

2.4.2 Diagenesis of the Footwall of the Paleokarstic Surface Host rocks that underlie the paleokarstic surface have also been subjected to numerous diagenetic alterations in various diagenetic environments from the time of its deposition until the present. However, the most important for today’s diagenetic appearance is the emplacement of carbonates in a meteoric diagenetic environment soon after its deposition or during the eugenetic stage of diagenesis. In carbonate rocks immediately below the paleokarstic surface differences in diagenesis can be observed already in the field (i.e. different staining and recrystallization of certain parts of the bedrock below the paleokarstic surface, patchy development of secondary porosity, etc.). The most complex paragenetic sequences occur in moulds of primarily aragonitic parts of rudist shells and their intraskeletal pores, as well as in bioturbation burrows and secondary dissolutional vugs. Depending on the position of the sampling, due to the inhomogeneous nature of the diagenetic alteration of the rock, as many as twelve early diagenetic phases have been recognized at some localities (Otoničar 2006, 2016).

M. Blatnik et al.

2.4.3 Stratigraphy of the Paleokarst Besides the research on paleokarst related phenomena, the study of the sedimentary successions of the host rock in which the paleokarstic features occur and of the strata that overlies the paleokarstic surface is of crucial importance to understanding the uplift of a substantial part of the AdCP above the sea-level in the Late Cretaceous and Paleogene. The age of limestones that immediately underlie the unconformity and the extent of the chronostratigraphic gap in the SW Slovenia and Istria systematically increases from northeast to southwest (Fig. 2.9a, b), while the age of the overlying limestones decreases in this direction (Fig. 2.9c). In the western part of Istria, the orientation of the isochrones is slightly different and indicates a dome-like topography of the subaerially exposed area. Data were obtained from 36 geological profiles in karstic regions of the SW Slovenia, the Slovenian and Croatian parts of the Istria Peninsula, and an area between the Trieste Bay and the Italian–Slovenian border in NE Italy (red dots in Fig. 2.9). The youngest rocks below the unconformity are Campanian and occur in the central and northern parts of the Kras (Karst) Plateau (the Komen Thrust Sheet) (Fig. 2.1) (Jurkovšek et al. 1996; Venturini et al. 2008; Dalla Vecchia 2009) and close to Postojna (the Snežnik Thrust Sheet) (Fig. 2.1) (Šribar 1995; Rižnar 1997) in the SW Slovenia, while the oldest strata, Valanginian and Hauterivian in age, crop out in the western part of Istria in the NW Croatia (Matičec et al. 1996) (Figs. 2.1 and 2.9a). The beds that cover the unconformity are of different ages, lithofacies, members and formations. As mentioned above, the age trend of the immediate cover is opposite to that of the footwall. In this case, the oldest rocks occur in SW Slovenia and NE Italy (between Trst/Trieste and Gorica/Gorizia) and belong to the youngest stage of the Late Cretaceous, the Maastrichtian or even the late Campanian/early Maastrichtian (Venturini et al. 2008; Dalla Vecchia 2009). Towards the southwest in general, progressively younger deposits onlap the paleokarstic surface (Fig. 2.9c). The documented chronostratigraphic gap, however, increases considerably from few Ma on the Kras plateau (SW Slovenia) to more than 80 Ma in western Istria (Fig. 2.9b). The thickness of the Kras Group generally decreases from NE towards SW, although significant deviations may occur (Fig. 2.10). A line where the unconformity pinches out towards the foreland basin occurs somewhere between the NE part of the Kras plateau on the Komen Thrust Sheet and some 10 km (approx. 25 km in the original position; see Placer 1998) distant at Mt. Nanos on the Hrušica Nappe (Fig. 2.1). From this line on towards the NE, the uplift above the sea-level did

2

Late Cretaceous and Paleogene Paleokarsts …

23

Fig. 2.9 Isochrones (in millions of years) of a the carbonate rocks that directly underlie the paleokarst surface, b the extent of the chronostratigraphic gap, and c the carbonate rocks that directly overlie the

paleokarst surface. The figures also show the main structural characteristics of the area and the locations of the geological sections considered (after Otoničar 2007)

not occur and the area experienced only subsidence (see above and Fig. 2.5). In this area, the sedimentary succession of the Adriatic Carbonate Platform gradually passes into a progressively deeper marine carbonate succession of a synorogenic carbonate platform. Namely, at the Campanian– Maastrichtian boundary, on Mt. Nanos and the Hrušica Plateau, the deepening of the shallow-marine carbonate platform without any evidence of preceding emersion can be seen (Fig. 2.5) (Šribar 1995; Jež and Otoničar 2010, 2018). Further towards the northeast, in the Julian Alps (the eastern part of the Southern Calcareous Alps) and in the northern-most part of the recent Dinaric mountain belt in western Slovenia and northeastern Italy (i.e. the Trnovo Nappe), the turbiditic siliciclastic sediments (i.e. the flysch) began to be deposited in the Campanian and Maastrichtian over the rocks of different lithology, age and origin (Pavšič 1994). The flysch often overlies deeper marine pelagic marls of the ‘scaglia’ type and alodapic carbonates which comprise a material derived from the AdCP. The oldest pelagic marls (i.e. pre-flysch deposits) which overlie the Upper Cretaceous

shallow-marine carbonates of the northeastern margin of the AdCP also belong to the Maastrichtian. Similarly to the chronostratigraphic gap, the pelagic marls and the flysch deposits are also diachronous over the area. Systematic trends expressed by isochrones showing the age of the carbonate rocks that immediately under- and overlie the paleokarstic surface (Fig. 2.9a, c), and consequently, the extent of the chronostratigraphic gap (Fig. 2.9 b), can be explained mainly by topography and the evolution of a peripheral foreland bulge (the forebulge) (Fig. 2.11).

2.4.4 Discussion When the foreland continental lithospheric plate was vertically loaded by the fold-and-thrust belt, it responded with a flexure. In front of the evolving orogen an asymmetric foreland basin was formed; the deepest part of the basin (the foredeep) is located adjacent to the orogenic wedge (Fig. 2.11). Because of the isostatic rebound on the vertical

24

M. Blatnik et al.

Fig. 2.10 Lithostratigraphic columns of three locations in the Matarsko Podolje and on Mt. Slavnik. Despite the proximity of the locations, we can observe considerable differences in thicknesses of the lithostratigraphic units and ranges of the stratigraphic gap (after Otoničar 2007)

loading of the lithosphere, the side of the basin opposite the orogenic wedge was instantaneously upwarped and a bulge with a subtle relief was formed, the peripheral bulge or the forebulge (Fig. 2.11). The bulge is particularly well expressed in the early, flysch stage of the foreland basin evolution (Crampton and Allen 1995). While the wavelength of the deflection is approximately the same for both, the foreland basin and peripheral bulge, the amplitude of the basin subsidence was typically much greater than the uplift of the bulge (Crampton and Allen 1995; Miall 1995). If the conditions are suitable, synorogenic carbonate platforms with distinctive ramp topography may colonise the gentle slope of the forebulge toward the foredeep (Dorobek 1995). Significantly, as the whole complex of the orogenic wedge advanced forelandward, the flexural profile produced by the orogenic wedge advanced with it. The topography of the forebulge is controlled by numerous factors, among which the rigidity of the foreland lithospheric plate and the rate of emplacement of the load are the most important

(Allen and Allen 1992; Dorobek 1995; Miall 1995). An expected maximal height of the forebulge above the sea-level (if the foreland plate is at or close to sea-level prior to flexural loading) would be in the range from a few tens to a few hundreds of metres (Crampton and Allen 1995; Miall 1995). Depending on the topography of the forebulge, the rate of erosion and the style of migration of the orogenic wedge, the area of maximal denudation should occur in the central part of the region, which is over-passed by the bulge (Crampton and Allen 1995). In addition, non-flexural deformations (e.g. reactivation of pre-existing heterogeneities, enhanced deflections because of horizontal in-plane stresses, etc.) and an inherited topography may significantly influence the evolution and topography of the forebulge (Allen and Allen 1992; Dorobek 1995; Miall 1995; Crampton and Allen 1995). Due to the stratigraphic position of the pinch-out line, where unconformity reduces to conformity, the trends of the unconformity related isochrones elsewhere (Fig. 2.9a–c) and

2

Late Cretaceous and Paleogene Paleokarsts …

25

Fig. 2.11 Schematic block diagram of the foreland basin system showing the position of the orogenic wedge, a deep-marine section of the foreland basin (the foredeep) and the peripheral bulge (the

forebulge). The model also shows the distribution of macrofacies before the completion of tectonic plate convergence (adapted from Bradley and Kidd 1991)

the age of the oldest pelagic marls and flysch, it is suggested that the northern sector of the AdCP had thrived more or less prosperously at least till the end of the Campanian when an initial uplift of the forebulge occurred. The carbonate sediments that had originally been deposited till that time, and are now missing in carbonate successions immediately below the unconformity, had been erased during the paleokarstic period by the karstic denudation processes. Due to the topography of the forebulge and the advancing nature of the foreland geodynamic complex as a whole, the most extensive denudation is expected to occur in the central area over which the forebulge migrated. The western part of Istria, where the chronostratigraphic gap is the largest and beds immediately below the unconformity are the oldest (Fig. 2.9a, b), most probably corresponds to this zone. However, in an ideal conceptual/mathematical model of the forebulge unconformity, the amount of erosion should remain more or less constant over a vast area in the central part of the region over-passed by the bulge, and decrease on its distal slope towards the back-bulge basin (Crampton and Allen 1995). Instead, in western Istria, the isochrones of the beds underlying the unconformity show distinctive condensation compared to the situation in NE Istria and SW Slovenia (Fig. 2.9a). We suggest that this is not the result of a rapid increase in the amount of the footwall eroded, but

rather of a denudation of primarily much thinner Cretaceous carbonate successions in western Istria (see above and Matičec et al. 1996; Otoničar 2007), partly due to repeating emersions throughout the Cretaceous (see above and Velić et al. 1989) and partly because of a reduced accommodation space for the Cretaceous shallow-marine environments. Evidence for considerable Late Jurassic and Cretaceous land areas in the vicinity of the western Istria (probably offshore from its recent west coast) came also from the dinosaur record (footprints and bones) (Dalla Vecchia et al. 2000; Mauko and Florjančič 2003; Mezga et al. 2003) and the distribution of sedimentary facies in the adjacent peritidal to deeper marine environments of the intraplatform basins (Tišljar et al. 1995, 1998). It is also possible that the central zone of the forebulge and the slope towards the back-bulge area in their final position occurred offshore of the recent Istrian west coast. However, we should be aware that in the Late Cretaceous the AdCP was surrounded by the western side by deeper marine interplatform basins (Vlahović et al. 2005) that could have considerably affected the appearance of the forebulge and the back-bulge area. Although the ‘abnormal thickness’ of denuded stratigraphy of western Istria is mainly the result of the previous depositional history, some uncertainties may also arise from differential uplift/subsidence of certain parts

26

of the forebulge. Evidence for differential subsidence along reactivated ancient tectonic structures is, for example, well documented in the carbonate successions of the Kras Group, where the thickness of chrono- and lithostratigraphic units may vary considerably over short distances (Fig. 2.10). In conclusion, we suggest that denudation processes exposed the oldest carbonate rocks in western Istria partly due to specific evolution (migration) and the topography of the forebulge and partly due to primarily thinner carbonate successions in this part of Istria compared to more northeastern parts of the study area. The rate of transgression over the paleokarstic surface is expressed by the isochrones of the strata that onlap the unconformity (Fig. 2.9c). While a large-scale diachronism of the onlapping strata shown in Fig. 2.9c is the result of specific large-scale topography and migration of the forebulge as a whole, local small-scale spatial differences in the onlap pattern (not observable in Fig. 2.9c) may be due to shorter oscillations of relative sea-level and deposition over the topographically irregular paleokarstic surface (e.g. dolines, shafts…—a ‘blue hole phase’ of the transgression). Composite unconformities, small-scale paleokarstic surfaces and pedogenic modifications in the lower part of the overlying Liburnian Formation also indicate relative sea-level oscillations during the main paleokarstic period. This could be the result not only of eustatic sea-level oscillations but also of changes in sediment supply and processes at the plate boundaries (i.e. formation of a new thrust complex, transition from passive to active thrusting phase, increase in compressive in-plane stress, etc.) in combination with rheological/structural characteristics of the foreland plate itself (see Allen and Allen 1992; Dorobek 1995; Crampton and Allen 1995).

2.4.4.1 Evolution of the Phreatic Caves In addition to the study of depositional successions and surface morphological features related to the subaerial exposure of a carbonate platform, underground studies, particularly of phreatic cavities and caves, can help us to better understand certain features and processes related to the relative uplift of the carbonate platforms above the sea-level. In modern subaerially exposed carbonate platforms and young carbonate islands, laterally extensive but vertically restricted caves with irregular walls and discrete horizons of spongy porosity are mainly characteristic of phreatic diagenetic environments related to freshwater lenses (Mylroie and Carew 1995a, b). In the study area, phreatic caves are frequently completely filled with deposits originating in a vadose zone, such as flowstone and bauxite, or they had been opened to the paleokarstic surface by complete denudation of the cave ceiling. In addition to pedogenically modified carbonate rocks cave filling deposits immediately below the paleokarst surface, often express pedogenic

M. Blatnik et al.

features. Caves with deposits that show no apparent origin in the vadose zone are usually smaller and situated deeper below the paleokarstic surface. Yet internal deposits in these caves, usually silty carbonate material and coarse-grained cements, have isotopic signatures characteristic of meteoric water diagenesis. Some cave deposits show alternating deposition of detrital sediments, cements and speleothems, interrupted by episodes of chemical and mechanical erosion that may result from relative sea-level oscillations, and consequently an underground water table, and/or hydrogeochemical conditions in a fresh/brackish water lens. While most of the phreatic cavities have been subsequently placed in the vadose zone prior to their submergence and burial, this process appears to have occurred in an oscillatory manner. According to the proposed simple model for dissolutional/filling evolution of phreatic caves related to fresh/brackish water lenses in a forebulge setting (see above and Fig. 2.12) all the phreatic caves that were uplifted, transformed and filled in vadose or epiphreatic zones should have formed below the flank of the forebulge facing the back-bulge area. However, short-term sea-level oscillations have been recognized not only from the characteristics of cave-related deposits but also from the carbonate succession that immediately overlies the paleokarstic surface (see above). Thus, in the lower part of the Liburnian Formation (which at least from the Late Cretaceous till early Eocene had to be deposited adjacent to the still subaerially exposed forebulge), the successions are commonly interrupted by short-term subaerial exposure surfaces with pedogenic and dissolutional characteristics. Short-term, relative sea-level oscillations also influenced the position of the fresh/brackish water lens below the adjacent uplifted part of the forebulge. Consequently, a relative underground water table fall of just a few metres would, for example, expose caves in the upper part of the lens to the vadose conditions where they could be filled with flowstone and sediments from the paleokarstic surface, especially if the vadose zone is relatively thin with well-developed interconnected subsurface vadose cavities (channels, pits, shafts, root casts, etc.). If we suppose that at least most extended paleokarstic caves originated close to the margin of the uplifted forebulge (i.e. flank margin caves of Mylroie and Carew 1995a, b or Quintana Roo-type caves of Smart et al. 2006) or were situated at the interface between phreatic in vadose zones (i.e. Banana Holes of Harris et al. 1995) then the paleokarstic surface was probably quite close to the phreatic caves, which could also increase the filling ability of these caves. As mentioned above, besides eustatic sea-level oscillations, processes at plate boundaries and the rheological/structural characteristics of the foreland plate itself may cause somewhat shorter term relative oscillations

2

Late Cretaceous and Paleogene Paleokarsts …

Fig. 2.12 Successive sketches of the evolution of phreatic caves related to forebulge migration (see text for explanation; extreme vertical exaggeration in comparison to horizontal distances). Grey to black coloured strips represent passive margin carbonate platform sequences, while brownish strips show different generations of underfilled foreland basin deposits (e.g., synorogenic carbonate platform). T1, T2, T3 geomorphological characteristics of the forebulge complex in three successive time-snaps; P1, P2, P3 position of the forebulge crest at different times; ft flank margin or coastal caves developed below the flank facing the foreland basin; bt flank margin or coastal caves developed below the flank facing the back-bulge area; ct caves developed in the upper part of the fresh/brackish water lens (i.e. banana holes by Harris et al. 1995) situated below the crest of the forebulge; L fresh/brackish water lens

of an underground water table. The extent and hydrogeochemical conditions of a fresh/brackish water lens can also be changed without relative sea-level oscillations, either by climate change or by diagenetic/karstic evolution of the aquifer (see Mylroie and Carew 1995b). Because of its specific diachronous nature of the karstified unconformity, a direct comparison between the paleocave levels among different locations even if they occur at the same depth below the paleokarstic surface is impossible.

27

2.4.4.2 Geotectonics As shown above, the structural and stratigraphic data indicate the evolution of an advancing orogenic wedge and a migrating synorogenic foreland basin complex resulting from collision processes (e.g. Allen and Allen 1992; Crampton and Allen 1995; Miall 1995). At first glance it seems normal to link the foreland complex with a tectonic phase that generated structures mainly by NE–SW compression (the mesoalpine phase of some authors; see Doglioni and Bosellini 1987) and gave rise to the formation of the Dinaric mountain belt at the end. However, the Dinaric orogenic belt where final uplift occurred during the Oligocene–Miocene (Vlahović et al. 2005) is supposed to be the result of collision between the Tisia and Adria microplates with onset of collision occurring during the Eocene (Pamić et al. 1998; Pamić 2002), which also coincides with the age of the oldest (preserved?) synorogenic deposits of the ‘coastal’ part of the External Dinarides (Marjanac and Ćosović 2000). On the contrary, although the nappe structures of the western Slovenia and the Late Cretaceous–Paleogene compressional deformations of the northeastern Italy indicate NE–SW or ENE–WSW compression, and so the ‘Dinaric’ orientation of the prevailing regional stress, the oldest foreland basin deposits in these regions supposed to be much older than those of other parts of the External Dinarides and belong to the latest stages of the Late Cretaceous (Otoničar 2007). It should be noted that in Istria the Tertiary tectonic cycle (from Eocene onward) displays the distinctively different orientation of the prevailing stress than the Mesozoic one (Marinčić and Matičec 1991; Matičec et al. 1996). Furthermore, the age distribution of the flysch deposits of the western Slovenia and Istria indicates an advancing nature of the foreland basin evolution from NE towards SW, which is in accordance with the ‘Dinaric’ orientation of the prevailing regional stress (Otoničar 2007). While south of the Zagreb–Zemplen fault line, the remnants of the oceanic lithosphere (i.e. ophiolite melange), as well as subduction and collision related rocks of the Internal Dinarides (i.e. the ‘Sava–Vardar Zone’ by Pamić et al. 1998 or the ‘Sava Zone’ of Schmid et al. 2008), which could be linked with closing processes of the Vardar Ocean and collision between Tisia and Adria microplates (Pamić 2000) are widespread, north from the Zagreb–Zemplen line no such rocks have been found so far. It seems possible that in central Slovenia, in prolongation of the Sava Zone, such rocks have been buried by the Tertiary sediments and the Southern Alpine nappes. An initial late Campanian?/Maastrichtian uplift of the forebulge coincides with an onset of the Sava Zone thrusting over the Western Vardar Ophiolitic Zone and formation of

28

M. Blatnik et al.

an underfilled basin where the Maastrichtian turbiditic siliciclastics overlay Campanian ophiolites and pelagic sediments which possibly suggests a trench front of the advancing European plate during subduction of the remaining Mesozoic Neo-Tethys (see Ustaszewski et al. 2010). This scenario is supported by the thermal evolution and metamorphism in the Sava Zone where maximum P–T conditions indicate tectonic burial of the most internal slices of the Adria continental lithosphere underneath the Europe-derived Tisza–Dacia plate (i.e. the Adria–Europe collision) at around 65 Ma (see Ustaszewski et al. 2010). In addition, on the NNE side, a nappe structure of Western Slovenia was cut from its ‘root zone’ by the Periadriatic Fault. The ‘root zone’ must have been displaced for at least 100 km eastward during the Miocene (Ratschbacher et al. 1991; Frisch et al. 1998; Vrabec and Fodor 2006). In conclusion, the foreland basin complex in the western Slovenia and Istria was probably formed during mesoalpine (‘Dinaric’) tectonic phase. The time discrepancy and also the exact orientation of the prevailing regional stress are probably the result of an oblique collision between the Adria and Tisza– Dacia plates (with an intermediate Sava Zone) and/or segmentation of the foreland plate (see Ricci-Lucchi 1986; Allen and Allen 1992). The Oligocene to recent tectonic events, especially in the Dinarides and Apennines, and the counterclockwise rotation of the Adria plate significantly modified the area formerly occupied by the forebulge.

2.5

Conclusion

Regarding the stratigraphy and topography of the subaerially exposed parts of the northern sector of the AdCP both of the Late Cretaceous paleokarsts discussed here owe their origin to tectonic processes induced at the adjacent plate boundaries of the western Neo-Tethys. However, two major indicative differences have been observed between the paleokarsts. In the case of the older paleokarst, a stratigraphic gap and the age of the footwall increases from SW towards NE (a general trend in a recent position) or from the inner parts of the platform towards its marginal parts, respectively. However, with the younger paleokarst, these items increase in the opposite direction, that is from NE to SW and covered mainly the inner parts of the platform. It is also characteristic that the transgression over the older paleokarstic surface occurred rather simultaneously while the age of the transgressive deposits that directly overlay the younger paleokarstic surface systematically decreases from NE (i.e. late Campanian(?)/Maastrichtian) towards SW (i.e. middle Eocene). It has also been speculated that, in fact, both

the paleokarsts represent one and the same paleokarstic period/event (Korbar, pers. comm.) developed on two geographically separated parts of the AdCP dissected by a deeper marine interplatform basin (see Korbar 2009). It is clear, however, from the evidence presented above that both paleokarsts are clearly separated spatially and temporally and without any deeper marine intraplatform basin between them. Further evidence for discontinuity between the two paleokarsts is also given by their evolution and topography because the gradual uplift above the sea-level that prograded from the outermost margin (NE) towards the inner parts of the platform (SW) and the limited vertical extent of the older paleokarst, as well as more or less simultaneous transgression over the paleokarstic surface, the rate of the relative uplift, proceeded more or less hand in hand with the denudation rate, or there were some significant periods of quiescence during the general relative lifting of the area when the subaerially exposed topography was levelled (Jež and Otoničar 2018). On the contrary, the extent of the stratigraphic gap, the age of the hanging-wall and the footwall of the younger paleokarst, the much larger vertical extent of the paleokarst in the central part of the uplifted area and also the temporal and spatial distribution of the overlying formations (i.e. the carbonate succession of the Kras Group and overlying siliciclastics–marlstone and flysch) indicate more or less continuous migration of the subaerially uplifted area and the overlying formations from NE towards SW. In this respect, the older paleokarst represents a part of the ‘static’ flexural profile developed over the northern sector of the AdCP in response to compressional in-plane horizontal stresses induced by events in the remnants of the Vardar Ocean (i.e. possible events related to an onset of the subduction and formation of the Sava Back-arc Ocean), indicated also by accelerated tectonic activity in the Tisza and Dacia Mega-Units and perhaps also in the Inner Dinarides (see Schmid et al. 2008). It should also be noted that in the Turonian large parts of the highly deformed Austroalpine domain had been elevated above the sea-level during a climax of the Eoapline orogeny (Faupl and Wagreich 2000). At the Campanian/Maastrichtian boundary the tectonic character of the northern sector of the AdCP changed from a ‘static’ profile to an advancing flexural profile in response to a vertical loading of the foreland lithospheric plate by the advancing fold-and-thrust belt resulting from collision between the Adria and Tisza–Dacia plates (with an intermediate Sava Zone) (see Schmid et al. 2008). In this respect, the younger paleokarst represents a subaerially exposed and karstified upwarped part (i.e. the forebulge) of a dynamic migrating synorogenic foreland basin complex.

2

Late Cretaceous and Paleogene Paleokarsts …

References Allen PA, Allen JR (1992) Basin analysis—principles & applications. Blackwell Science, London, p 451 Bosák P, Ford DC, Glazek J (1989) Terminology. In: Bosák P, Ford DC, Glazek J, Horaček I (eds) Paleokarst—a systematic and regional review. Elsevier, Amsterdam, pp 25–32 Bosellini A (1989) Dynamics of Tethyan carbonate platforms. In: Crevello PD, Wilson JL, Sarg JF, Read JF (eds) Controls on carbonate platforms and basin development. Society of Economic Paleontologists and Mineralogists, Tulsa, pp 3–13 Bradley DC, Kidd WSF (1991) Flexural extension of the upper continental crust in collisional foredeeps. Geol Soc Am Bull 103:1416–1438 Buser S (1989) Development of the Dinaric and the Julian carbonate platforms and of the intermediate Slovenian basin (NW Yugoslavia). Mem Soc Geol Ital 40(1987):313–320 Cousin M (1981) Les rapports Alpes-Dinarides. Les confins de l’Italie et de la Yougoslavie. Soc Gol Nord 5:1–521 Crampton SL, Allen PA (1995) Recognition of forebulge unconformities associated with early stage foreland basin development: example from the North Alpine foreland basin. AAPG Bulletin 79 (10):1495–1514 Dalla Vecchia FM (1998) Theropod footprints in the Cretaceous adriatic-dinaric carbonate platform (Italy and Croatia). Gaia 15:355–367 Dalla Vecchia FM (2001) Terrestrial ecosystems on the Mesozoic peri-Adriatic carbonate platforms: evidence. Asociacion Paleontologica Argentina, Publicacion Especial 7, VII international symposium on the vertebrate mesozoic terrestrial ecosystems, Buenos Aires, pp 77–83 Dalla Vecchia FM (2009) Tethyshadros insularis, a new Hadrosauroid dinosaur (Ornithischia) from the upper Cretaceous of Italy. J Vertebr Paleontol 29(4):1100–1116 Dalla Vecchia FM, Tarlao A, Tentor M, Tunis G, Venturini S (2000) First record of Hauterivian dinosaur footprints in southern Istria (Croatia). In: Vlahović I, Biondić R (eds) 2. Hrvatski geološki kongres, Cavtat-Dubrovnik, 17–20 May 2000, Zbornik radova. Institut za geološka istraživanja, pp 143–149 D’Argenio B, Mindszenty A (1995) Bauxites and related paleokarst: tectonic and climatic event markers at regional unconformities. Eclogae Geol Helv 88(3):453–499 Debeljak I, Košir A, Otoničar B (1999) A preliminary note on dinosaurs and non-dinosaurian reptiles from the Upper Cretaceous carbonate platform succession at Kozina (SW Slovenia) = Preliminarno obvestilo o dinozavrih in drugih reptilih iz zaporedja zgornjekrednih platformnih karbonatov pri Kozini (JZ Slovenija). Razpr.- Slov. akad. znan. umet. Razr. naravosl. vede 40:3–25 Debeljak I, Košir A, Buffetaut E, Otoničar B (2002) The late Cretaceous dinosaurs and crocodiles of Kozina (SW Slovenia): a preliminary study. Mem Soc Geol Ital 57:193–201 Doglioni C, Bosellini A (1987) Eoalpine and Mesoalpine tectonics in the Southern Alps. Geol Rundsch 76(3):735–754 Dorobek SL (1995) Synorogenic carbonate platforms and reefs in foreland basins: controls on stratigraphic evolution and platform/reef morphology. In: Dorobek SL, Ross GM (eds) Stratigraphic evolution of foreland basins, Special publication No. 52. SEPM, Tulsa, pp 127–147 Dragičević I, Velić I (2002) The Northeastern margin of the adriatic carbonate platform. Geologia Croatica 55:185–232

29 Durn G, Ottner F, Tišljar J, Mindszenty A, Barudžija U (2003) Regional subaerial unconformities in shallow-marine carbonate sequences of Istria: sedimentology, mineralogy, geochemistry and micromorphology of associated bauxites, palaeosols and pedo-sedimentary complexes. In: Vlahović I, Tišljar J (eds) 22nd IAS meeting of sedimentology, field trip guidebook, Opatija, pp 209–254 Faupl P, Wagreich M (2000) Late Jurassic to eocene paleogeography and geodynamic evolution of the eastern Alps. Mitt Österr Geol Ges 92:79–94 Frijia G, Parente M, Di Lucia M, Mutti M (2015) Carbon and strontium isotope stratigraphy of the upper Cretaceous (Cenomanian–Campanian) shallow-water carbonates of southern Italy: chronostratigraphic calibration of larger foraminifera biostratigraphy. Cretac Res 53:110–139 Frisch W, Kuhlemann J, Dunkl I, Brugel A (1998) Palinspastic reconstruction and topographic evolution of the eastern Alps during late tertiary tectonic extrusion. Tectonophysics 297(1–4):1–15 Gabrić A, Galović I, Sakač K, Hvala M (1995) Mineral deposits of Istria. Some deposits of bauxite, building-stone and quartz “sand”. Excursion guide-book. First Croatian geological congress, 18– 21.10.1995, Opatija, Zagreb, pp 111–137 Galić I, Krasić D, Dragičević I (2015) Evaluation of research in a bauxite-bearing area at the “Crvene stijene” locality with emphasis on exploration of the associated deposits. Geologia Croatica 68 (3):225–236 Goričan Š, Žibret L, Košir A, Kukoč D, Horvat A (2018) Stratigraphic correlation and position of Lower Cretaceous flysch-type deposits in the eastern Southern Alps (NW Slovenia). Int J Earth Sci 107 (8):2933–2953 Grötsch I (1994) Guilds, cycles and episodic vertical aggradation of a reef (late Barremian to early Aptian, Dinaric carbonate platform, Slovenia). Spec Publs Int Ass Sediment 19:227–242 Gušić I, Jelaska V (1990) Upper Cretaceous stratigraphy of the island of Brač. Opera Academiae scientiarum et artium Slavorum meridionalium 69, Zagreb, p 160 Gušić I, Jelaska V (1993) Upper cenomanian-lower turonian sea-level rise and its consequences on the adriatic-dinaric carbonate platform. Geol Rundsch 82:676–686 Haq BU (2014) Cretaceous eustasy revisted. Glob Planet Chang 113:44–58 Haq BU, Hardenbol J, Vail PR (1987) Chronology of fluctuating sea levels since the Triassic. Science 235(4793):1156–1167 Harris JG, Mylroie JE, Carew JL (1995) Banana holes—unique karst features of the Bahamas. Carbonates Evaporites 10(2):215–224 Jež J, Otoničar B (2010) Vpliv evstatičnih in tektonskih dogodkov na zgornjekredno dinamiko sedimentacije na severnem obrobju Jadranske karbonatne platforme: primer z Nanosa. In: Košir A et al. (eds) Povzetki in ekskurzije, 3. Slovenski geološki kongres, 16–18. September 2010, Bovec, Znanstvenoraziskovalni center SAZU, Inštitut za raziskovanje krasa, Paleontološki inštitut Ivana Rakovca, Postojna, Ljubljana, pp 24–25 Jež J, Otoničar B (2018) Late Cretaceous geodynamics of the northern sector of the Adriatic carbonate platform (W Slovenia). Newsl Stratigr 51(4):381–410 Jež J, Otoničar B, Fuček L, Ogorelec B (2011) Late Cretaceous sedimentary evolution of a northern sector of the Adriatic carbonate platform (Matarsko Podolje, SW Slovenia). Facies 57(3):447–468 Jones B (1992) Caymanite, a cavity-filling deposit in the Oligocene-Miocene Bluff formation of the Cayman Islands. Can J Earth Sci 29(4):720–736

30 Jones B, Kahle CF (1985) Lichen and algae—agents of biodiagenesis in karst breccia from Grand Cayman Island. Bull Can Pet Geol 33 (4):446–461 Jurkovšek B, Toman M, Ogorelec B, Šribar L, Drobne K, Poljak M (1996) Formacijska geološka karta 1:50.000 južnega dela Tržaško-Komenske planote (Geological map of the southern part of the Trieste—Komen plateau 1:50,000). Cretaceous and Palaeogene carbonate rocks. Inštitut za geologijo, geotehniko in geofiziko, Ljubljana, p 143 Jurkovšek B, Cvetko Tešović B, Kolar-Jurkovšek T (2013) Geologija Krasa (Geology of Karst). Geološki zavod Slovanije, Ljubljana, p 205 Klimchouk AB, Ford DC (2000) Types of karst and evolution of hydrogeologic setting. In: Klimchouk AB, Ford DC, Palmer AN, Dreybrodt W (eds) Speleogenesis-evolution of Karst Aquifers. National speleological society, Huntsville, pp 45–53 Korbar T (2009) Orogenic evolution of the external Dinarides in the Adriatic region: a model constrained by tectonostratigraphy of upper Cretaceous to Paleogene carbonates. Earth Sci Rev 96:296– 312 Košir A (2003) Litostratigrafska revizija zgornje krede in paleogena v jugozahodni Sloveniji. 16. Posvetovanje slovenskih geologov, Ljubljana, pp 92–98 Košir A, Otoničar B (2001) The evolution of upper Cretaceous and Paleogene synorogenic carbonate platforms in NW Dinaric Foreland Basin. In: Dragičević I, Velić I (eds) 1st scientific meeting on carbonate platform or carbonate platforms of Dinarids: abstracts, Zagreb, 1–2 October 2001. Rudarsko-geološko-naftni fakultet, Prirodoslovno-matemetički fakultet, Institut za geološka istraživanja i Hrvatsko geološko društvo, Zagreb, pp 62–63 Lohmann KC (1988) Geochemical patterns of meteoric diagenetic systems and their application to studies of paleokarst. In: James NP, Choquette PW (eds) Paleokarst. Springer, pp 58–80 Magaš N (1965) Osnovna geološka karta SFRJ. List Cres [Kartografsko gradivo] 1:100.000. Zvezni geološki zavod, Beograd Marinčić S, Matičec D (1991) Tektonika i kinematika deformacija na primjeru Istre. Geološki vjesnik 44:257–268 Marjanac T, Ćosović V (2000) Tertiary depositional history of eastern Adriatic realm. In: Tomljenović B, Balen D, Saftić B (eds) Pancardi 2000: fieldtrip guidebook, Dubrovnik, Croatia, 1–3 oktober 2000. Vijesti Hrvatskog geološkog društva: Special issue 37(2), Zagreb, pp 93–103 Matičec D, Vlahović I, Velić I, Tišljar J (1996) Eocene limestones overlying lower Cretaceous deposits of Western Istria (Croatia): Did some parts of present Istria form land during the Cretaceous? Geologia Croatica 49(1):117–127 Mauko A, Florjančič B (2003) Dinosaur footprints in the upper Turonian-Coniacian limestone in the Krnica Bay (NE Istria, Croatia) = Stopinje dinozavrov v zgornjeturonijsko-coniacijskem apnencu v zalivu Krnica (NE Istra, Hrvaška). Geologija 46(1):93– 100 Mezga A, Bajraktarević Z, Cvetko Tešović B, Gušić I (2003) Dinosaur tracks as an evidence for the terrestriality in the late Jurassic sediments of Istria, Croatia. In: Vlahović I (ed) Abstracts book. 22nd IAS meeting of sedimentology, Opatija 2003, Institute of geology, Zagreb, pp 126 Miall AD (1995) Collision-related foreland basins. In: Busby CJ, Ingersoll RV (eds) Tectonics of sedimentary basins. Blackwell Science, Cambridge. Massachusetts, USA, pp 393–424 Mylroie JE, Carew JL (1995a) Karst development on carbonate islands. In: Budd DA, Saller AH, Harris PM (eds) Unconformities and porosity in carbonate strata. AAPG Memoir 63:55–76 Mylroie JE, Carew JL (1995b) Geology and karst geomorphology of San Salvador island, Bahamas. Carbonates and Evaporites 10 (2):193–206

M. Blatnik et al. Orehek A, Ogorelec B (1976) Mezozoik v Sloveniji—mikrofacialna in litološka razčlenitev mezozoiskih kamenin na Primorskem. Ljubljana, Geološki zavod Ljubljana, p 25 Osborne RAL (2000) Paleokarst and its significance for speleogenesis. In: Klimchouk AB, Ford DC, Palmer AN, Dreybrodt W (eds) Speleogenesis–Evolution of Karst Aquifers. National Speleological Society, Huntsville, pp 113–123 Osborne RAL (2008) Cave turbidites. Acta Carsolog 37(1):17–26 Otoničar B (2006) Razvoj paleokrasa v zgornjekrednih apnencih Matarskega podolja in Slavnika = Paleokarst development in the Upper Cretaceous limestones of Matarsko Podolje and Slavnik. Ph. D. Thesis, Univerza v Ljubljani, Naravoslovnotehniška fakulteta, Oddelek za geologijo, Ljubljana, p 309 Otoničar B (2007) Upper Cretaceous to Paleogene forebulge unconformity associated with foreland basin evolution (Kras, Matarsko Podolje and Istria; SW Slovenia and NW Croatia). Acta Carsolog 36(1):101–120 Otoničar B (2016) Kozina (No. 1 & 2): the 75 MA long history of karstification of the Upper Cretaceous and Lower Paleogene limestones at Kozina. In: Otoničar B, Gostinčar P (eds) Paleokarst: abstracts & guide book, 24th International Karstological School Classical Karst, Postojna 2016. Karst Research Institute, Research Centre of the Slovenian Academy of Sciences and Arts, Ljubljana, pp 51–64 Otoničar B, Jež J (2012) Carbon and oxygen isotope stratigraphy of Late Cenomanian to Santonian shallow-marine carbonate succession of Mt. Nanos, W Slovenia. In: Missoni S, Gawlick H-J (eds) Sedimentology in the heart of the Alps, 29th international association of Sedimentologists meeting of sedimentology, 10–13 September 2012, Schladming, Austria, p 577 Otoničar B, Košir A, Ćosović V (2003) Cretaceous-Tertiary paleokarst from Koromačno (Istria, NW Croatia): an example of paleokarstic denuded cave. In: Vlahović I (ed) 22nd IAS Meeting of Sedimentology, Opatija. e-Abstracts book, Institute of geology, Zagreb, p 146 Pamić J (2000) The Sava-Vardar zone (SVZ). In: Tomljenović B, Balen D, Saftić B (eds) Pancardi 2000: fieldtrip guidebook, Dubrovnik, Croatia, 1–3 October 2000. Vijesti Hrvatskog geološkog društva, Special issue 37(2):19–22 Pamić J (2002) The Sava-Vardar zone of the Dinarides and Hellenides versus the Vardar Ocean. Eclogae Geol Helv 95(1):99–113 Pamić J, Gušić I, Jelaska V (1998) Geodynamic evolution of the central Dinarides. Tectonophysics 297(1–4):251–268 Pavšič J (1994) Biostratigraphy of Cretaceous paleocene and eocene clastics of Slovenia. Razprave Slov. akad. znan. umet. Razr. naravosl. vede 35:66–84 Placer L (1981) Geološka zgradba jugozahodne Slovenije/Geologic structure of southwestern Slovenia. Geologija 24(1):27–60 Placer L (1998) Contribution to the macrotectonic subdivision of the border region between southern Alps and external Dinarides. Geologija 41:223–255 Placer L (2004) Predhodna objava rezultatov strukturnega profiliranja Kraškega roba in Istre (AC Kozina – Srmin, Sečovlje) = Preliminary results of structural profiling of the Kras edge and Istria (AC Kozina—Srmin, Sečovlje). Geologija 45(1):277–278 Ratschbacher L, Frisch W, Linzer HG, Merle O (1991) Lateral extrusion in the Eastern Alps 2: Structural analysis. Tectonics 10 (2):257–271 Ricci-Lucchi F (1986) The Oligocene to recent basins of the northern Apennines. In: Allen PA, Homewood P (eds) Foreland basins. Spec Publs Int Ass Sediment—IAS. Blackwell, Oxford, pp 105–139 Rižnar I (1997) Geologija okolice Postojne. Magistrsko delo, Univerza v Ljubljani, Naravoslovnotehniška fakulteta, Oddelek za geologijo, Ljubljana, p 78

2

Late Cretaceous and Paleogene Paleokarsts …

Schlager W (1981) The paradox of drowned reefs and carbonate platforms. Geol Soc Am Bull 92(4):197–211 Schlager W (1999) Type 3 sequence boundaries. In: Harris PM, Saller AH, Simo JAT (eds) Advances in carbonate sequence stratigraphy: application to reservoirs, outcrops, and models. SEPM Special Publication, Society for Sedimentary Geology, Tulsa, pp 187–226 Schmid SM, Bernoulli D, Fügenschuh B, Matenco L, Schefer S, Schuster R, Tischler M, Ustaszewski K (2008) The Alpine-Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units. Swiss J Geosci 10:139–183 Sinclair HD (1997) Tectonostratigraphic model for underfilled peripheral foreland basins: an Alpine perspective. Geol Soc Am Bull 109 (3):324–346 Smart PL, Beddows PA, Coke J, Doerr S, Smith S, Whitaker FF (2006) Cave development on the Caribbean coast of the Yucatan Peninsula, Quintana Roo, Mexico. In: Harmon RS, Wicks CM (eds) Perspectives on karst geomorphology, Hydrogeology, and Geochemistry— a tribute volume to Derek C. Ford and William B. White. The Geological Society of America, Special paper 404, pp 105–128 Stampfli GM, Mosar J, Marquer D, Marchant R, Baudin T, Borel G (1998) Subduction and obduction processes in the Swiss Alps. Tectonophysics 296:159–204 Šribar L (1995) Evolucija Gornjekredne Jadransko-Dinarske karbonatne platforme u jugozapadnoj Sloveniji. Magistrski rad, Sveučilište u Zagrebu, Prirodoslovno-matematički fakultet, Zagreb, p 89 Tišljar J, Velić I (1991) Carbonate facies and depositional environments of the Jurassic and lower Cretaceous of the coastal Dinarides (Croatia). Geol Vjesnik 44:215–234 Tišljar J, Vlahović I, Matičec D, Velić I (1995) Platformni faciesi od gornjega titona do gornjega alba u zapadnoj Istri i prijelaz u tempestite, klinoformne i rudistne biolititne faciese donjega cenomana u južnoj Istri (ekskurzija B). In: Vlahović I, Velić I (eds) Vodič ekskurzija, 1. hrvatski geološki kongres. Institut za geološka istraživanja i Hrvatsko geološko društvo, Opatija, 18– 21.10.1995, Zagreb, pp 67–110 Tišljar J, Vlahović I, Velić I, Matičec D, Robson J (1998) Carbonate facies evolution from the late Albian to middle Cenomanian in

31 southern Istria (Croatia): influence of synsedimentary tectonics and extensive organic carbonate production. Facies 38:137–152 Uršič Arko A, Otoničar B (2019) Turonijsko do srednje coniacijsko zaporedje karbonatnih kamnin jugozahodnega krila Postojnske antiklinale. In: Rožič B (ed) 24th Meeting of Slovenian Geologists, Ljubljana. Geološki zbornik 25:142–143 Ustaszewski K, Kounov A, Schmid SM, Schaltegger U, Krenn E, Frank W, Fügenschuh B (2010) Evolution of the Adria-Europe plate boundary in the northern Dinarides: from continent-continent collision to back-arc extension. Tectonics 29(TC6017):34 Velić I, Tišljar J, Sokač B (1989) The variability of thicknesses of the Barremian, Aptian and Albian carbonates as a consequence of changing depositional environments and emersion in western Istria (Croatia, Yugoslavia). Mem Soc Geol Ital 40(1987):209–218 Velić I, Tišljar J, Vlahović I, Matičec D, Bergant S (2003) Evolution of the Istrian part of the Adriatic Carbonate Platform from the Middle Jurassic to the Santonian and Formation of the flysch basin during the Eocene: main events and regional compresion. In: Vlahović I, Tišljar J (eds) 22nd IAS meeting of sedimentology, Field trip guidebook, Opatija, pp 3–17 Venturini S, Tentor M, Tunis G (2008) Episodi continentali edulci coli ed eventi biostratigrafici nella sezione campaniano-maastrichtiana di Cotici (M. te San Michele, Gorizia). Natura Nascosta 36:6–23 Vlahović I, Tišljar J, Velić I, Matičec D (2005) Evolution of the Adriatic carbonate platform: palaeogeography, main events and depositional dynamics. Palaeogeogr Palaeoclimatol Palaeoecol 220 (3–4):333–360 Vrabec M, Fodor L (2006) Late Cenozoic tectonics of Slovenia: structural styles at the northeastern corner of the Adriatic microplate. In: Pinter N, Grenerczy G, Weber J, Stein S, Medak D (eds) The Adria microplate: GPS geodesy, tectonics and hazards. NATO Science Series IV, Earth and Environmental Sciences. Dordrecht, Springer, pp 151–168 Ziegler PA, Cloetingh S, Van Wees JD (1995) Dynamics of intra-plate compressional deformation: the Alpine foreland and other examples. Tectonophysics 252(1–4):7–59

3

Lithomorphogenesis of Karst Surface Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

The rock relief of karst phenomena is often a revealing and graphic trace of their formation and development. It is composed of rock forms. A relatively large number of dissertations (see Ginés et al. (eds) 2009) present examples, mostly of individual rock forms that developed on various carbonate rock in different environments with dominant local factors and processes. Many reports deal with identification of rock forms composing the rock relief and their logical classification according to forms and factors, and their importance in establishing the development of karst phenomena (Slabe 1995a; Ford and Williams 2007; Ginés et al. (eds) 2009). Due to various factors, karst phenomena take different shapes that are most often reflected in the rock relief. Through a series of different developmental factors, new factors first gradually transform traces of old formations and over time, if they are distinct enough, they can replace them with completely new ones (e.g. denudation of subsoil karren). Rock forms are therefore completely independent when shaped by a single factor or composite when they contain a distinct trace of an older form or when they are shaped by several factors at once. In places, old forms are reflected in the formation of a new rock relief only indirectly (e.g. denuded funnel-like notches on rock peaks). There are relatively few studies about this type of transformation of rock relief (Knez and Slabe 2011).

M. Blatnik
F. Gabrovšek
M. Knez (&)
B. Kogovšek
J. Kogovšek
C. Mayaud
A. Mihevc
J. Mulec
M. Năpăruş-Aljančič
B. Otoničar
M. Petrič
T. Pipan
M. Prelovšek
N. Ravbar
T. Shaw
T. Slabe
S. Šebela
N. Zupan Hajna Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia e-mail: [email protected] D. C. Culver American University, Washington, DC, USA H. Liu Yunnan University, Kunming, China

The rock relief of karst phenomena, in this case karren, also develops under the influence of a single factor. Developmentally, rock forms, often in several layers (e.g. funnel-like notches dissected by rain flutes), merge into one another. The type of rock and its geological history are, in addition to climatic conditions, soil cover and vegetation cover of the rocky surface, one of the most important reasons for the characteristic selective karstification. Geological research was devoted primarily to the lithostratigraphic rock composition; the fissuring of the rock, which influences the shape of the rock block; the stratification of the rock; the rock texture; microtectonics; and other aspects. Generally speaking, it is true that the type of rock is clearly reflected in the intensity of corrosion and erosion, and through it in the formation and morphological appearance of the surface of individual blocks of rock. Using a development model of surface rock relief formation of karst forms, we are able to illustrate the most characteristic patterns of its formation and transformation on different carbonate rock and its surroundings and according to various factors and processes. This type of approach helps supersede the too frequent descriptions and explanations based on existing conditions and provide the logical upgrading of previous findings on the formation and development of karst surfaces. At the same time, this approach is based on reliable knowledge of numerous examples around the world which is essential for any type of modelling, including the laboratory modelling of rock relief on plaster that verifies and complements the development model. Let this contribution on the analysis of the formation of carbonate rock by rain be a first step.

3.1

Formation of Karst Surface―Karren Worldwide

Formation of karren is influenced by diversity of carbonate rock, regional development with potential changing of factors and conditions with processes, and duration of formation that fosters rock dissection and developmental spillover of

© Springer Nature Switzerland AG 2020 M. Knez et al. (eds.), Karstology in the Classical Karst, Advances in Karst Science, https://doi.org/10.1007/978-3-030-26827-5_3

33

34

rock forms in the rock relief even under only one factor (Knez and Slabe 2010; Knez et al. 2010, 2011a, b, 2015, 2017; Gutiérrez et al. 2015; Urushibara Yoshino et al. 2017). All these factors can either be equally balanced or one factor can dominate completely and give the karren a special stamp.

3.1.1 Denudation and Transformation of Subsoil Karren One of the most characteristic developmental paths is denudation of subsoil-formed carbonate rock and then transformation of the subsoil rock relief as dictated by climate factors and surface biocorrosion. This path is revealed in all its diversity by examples from the Shilin Stone Forests, augmented by two examples in a similar environment and another example in different, Mediterranean conditions. In the introduction, explanations of the origin of characteristic subsoil features have been added, simplifying understanding of the descriptions that follow.

3.1.1.1 Significant Subsoil Rock Forms Shapes created on karst surfaces covered by soil or sediment are called “subsoil rock forms”. Detailed description is in the book Karst Rock Features, Karren Sculpturing (Slabe and Liu 2009, 123). Soil or various types of sediment that completely or partially cover carbonate rock influence shaping of the rock. Water flowing along the contact between the cover and the

Fig. 3.1 Subsoil cups

M. Blatnik et al.

rock creates subsoil channels and subsoil scallops. We can distinguish tiny forms at the most permeable contact between rock and soil. These include finely dissected channels, small cups, steps, and small pendants. Water that percolates through the soil forms subsoil cups and solution pipes. When so much water flows down the rock to the soil or sediment that it can not all flow away rapidly between the rock face and the soil or sediment, it carves out half-bells and notches. Unique rock forms also occur due to oscillation of the level of the water table. Due to relatively even dissolving of rock under soil and sediment, the rock is rounded as are the subsoil rock forms, and the surface of the rock is relatively smooth to the naked eye or characteristically rough on diversely-structured or recrystallized carbonate rock. Only the smallest subsoil rock forms deviate from these characteristics. Under great magnification, the subsoil rock surface as a rule is distinctly finely rough due to the even corrosion of the grained rock (Slabe 1994). Rock Forms Occurring Due to the Percolation of Water Through Soil and Sediment Under a thinner layer of porous soil that partly or entirely covers the rock, smaller and larger subsoil cups form on horizontal surfaces (Fig. 3.1). The former are 1–5 cm in diameter and the latter are larger. They occur due to the percolation of water through the soil to the rock. Special subsoil cups (see Fig. 3.33b) form under newly occurring weathered debris. As the exposed surface becomes

3

Lithomorphogenesis of Karst Surface

overgrown, disintegrating vegetation piles up on the rock, retaining moisture and accelerating the corrosion of the rock. The cups also form under moss, lichen, or algae that cover the rock in places. Subsoil Rock Forms Occurring Due to Flowing of Water along the Contact Between Rock and Soil or Sediment Subsoil channels form due to the concentrated flow of water along the contact with the soil. As a rule, the largest channels form when the water runs down vertical or steep contact points. These large (Fig. 3.2), usually vertical and separate channels have diameters 0.2–1 m and more. On more or less gently sloping rock covered by soil, channels with semicircular bottoms develop, being frequently described in the literature as “rundkarren” (Sweeting 1972, 93; Perna and Sauro 1978) and “subsoil runnels” (Trudgill 1985, 57). On steep surfaces, they can be parallel (Williams 1966, 164), and we can talk about subsoil flutes since the water percolating through the soil flows evenly over the entire surface.

35

Special channels, called “hohlkarren” by Sweeting (1972, 89), form when they are filled with soil or when their bottoms are covered and the rock around them is bare. Subsoil scallops (Fig. 3.3) occur due to the flow of water along the entire-permeable contact of the rock with the soil. These are subsoil cups with diameters 15–50 cm connected in a network. They are shallow and most often a little deeper in their upper part. As a rule, they are found on overhanging rock surfaces. Rock Relief of Subsoil Karren that is Periodically Flooded The peaks of subsoil karren that are periodically reached by the water table and are entirely formed below the ground are sharp. Relatively smooth rock characteristic of formation beneath soil and fine-grained sediment dominates the upper part. Subsoil notches are most pronounced in the lower part of the karren. Two dominant processes for the formation of this type of subsoil karren can be deduced from the shape of the karren and its rock relief. The rock forms that are traces of frequent oscillation of the level of the water table that floods the karren from below gives it a special stamp. When the water table is low, the karren is shaped by the water that periodically and dispersedly percolates from the surface through the soil and slides evenly down the rock. Minute Subsoil Dissection of Rock The walls of cracks through which water carries soil but does not fill them completely and dolines that are thinly covered with soil are often dissected by unique subsoil cups while overhangs are dissected with ceiling pendants. On gently sloping sections in such conditions, the rock is dissected by steps. Subsoil Tubes The rock below the ground is often crisscrossed by tubes of various sizes, karst hollows that during their formation are filled with sediment or soil. The larger ones are dissected in the rock relief by above-sediment (Slabe 1995a) and under-sediment channels. Rock Forms that Occur at the Level of the Soil or Sediment

Fig. 3.2 Subsoil channel

Subsoil notches form due to the corrosion of the rock along a long-lasting level of sediment or soil surrounding it. Water flows to the contact over a larger surface, more or less distinctly corrodes it, and then flows away between the rock and the soil. Smaller subsoil notches with diameters 10–20 cm have a shape of semicircular horizontal channels, only with their upper edges most often being sharper and the lower

36

M. Blatnik et al.

Fig. 3.3 Subsoil scallops

Fig. 3.4 Subsoil notch

edges more rounded. Larger subsoil notches (Fig. 3.4) like “undercut notches” (Waltham 1984, 182; Ford et al. 1997), “solution notches” (Jennings 1973, 48) and “swamp undercut” (Ollier 1984, 46) are corroded 1 m or more into the rock.

Half-bells (Fig. 3.5) form below channels that continuously bring larger quantities of water to the sediment or soil surrounding the rock. The contact is not conductive enough for all of the water that reaches it.

3

Lithomorphogenesis of Karst Surface

37

Fig. 3.5 Subsoil half-bell

3.1.1.2 Karren of Mushroom Mountain (Junzi Shan) in the Eastern Yunnan Ridge, a Karstological and Tourist Attraction (Yunnan, China) To a large extent, the method of its formation is dictated by parallel with stratification stylolitized rock, which at first glance (regional macroscopic level) appears as thinly layered carbonate (Knez and Slabe 2011). The carbonate rock in the area of Mushroom Mountain (Figs. 3.6 and 3.7) has a very even and gentle dip of strata (8°–12°). Throughout its geological history, the Triassic rock covered by very thick younger layers underwent the diagenetic process of chemical dissolution and stylolitization. The stylolitization occurred in parallel with stratification (Fig. 3.8a, b). Generally speaking, an outcrop of layers influenced by stylolitization indicates thin stratification, while the rock only recently denuded appears to be substantially more massive or apparently thickly layered. The weathering along the stratification and stylolitization below the soil is not pronounced. Under the ground (a few dozen cm below the surface) rock teeth form of relatively regular conical shape (Fig. 3.9). Once denuded, the rock rapidly reveals its true characteristics. Corrosion and erosion processes, especially along the contacts of layers and stylolites, intensively affect the outcrops. In a relatively short period of time, and with extensive help from moss and lichen (biochemical corrosion), the rock along these contacts becomes heavily weathered. On a fresh outcrop, we can observe a thin sheet of clay (insoluble remains) between individual layers or

horizons of carbonate rock. There are two possible reasons for the appearance of this thin, even laminar clay: either the clay is synsedimentary (El Torcal stone forest) or more probably it is the residue of a very strong diagenetic process of stylolitization. The laminar clays, regardless of their origin, are one of the basic reasons for the type of weathering we see on Mushroom Mountain. Due to the thin horizons of rock between individual layers and stylolites and to the laminar clay, the conical rock teeth or even the rock pillars cannot last long on the surface. On the contrary, the surface shows a trend of “levelling” according to stratification and in its “final” or current state appears as a “karst pavement”. Karren originally starts as a subsoil form (Fig. 3.7a). Under soil and sediment, more or less vertical fissures start to appear where water trickles downwards along the contact of soil and rock as well as along junctions in the rock. Subsoil channels (Fig. 3.7c) develop and subsoil shafts form that reach 1 m in diameter, often with a funnel-shaped mouth in the upper part. Horizontal or gently sloping subsoil channels with cross sections often shaped like an inverted Greek letter omega continue to dissect the karren tops as well. A good part of them are still filled with soil. In places, smaller subsoil tubes form along the junctions in the rock, often linked in anastomoses. Vegetation also penetrates them. The karren that have been denuded for a long period, which dominate the tops of the cones, have already been reshaped to a great extent by rain. Rain pits (Fig. 3.7e) are first formed on gently sloping surfaces, and flutes are the prevailing form on the dissected karren tops and their edges.

38

Fig. 3.6 Karren with flat top in the area of Mushroom Mountain Fig. 3.7 Karren with rock features: a subsoil karren, b and c subsoil channels, d solution pan, e rain pits and flutes

M. Blatnik et al.

3

Lithomorphogenesis of Karst Surface

39

Fig. 3.8 a Stratification is very distinct on denuded rock. b Stylolites are only few millimetres apart in places

Fig. 3.9 Pointed subsoil tops

Channels are formed between flutes on more extensive gently sloping karren tops. Rainwater scallops form on overhanging parts of the rock wall. Flat karren tops foster the formation of solution pans as well, which often develop from subcutaneous cups. The old cave that opens below the top of one of the cones is attractive and speleologically interesting. It reveals the period when this part of the karst was formed, before its

dissection into hills and cones when this part of the karst aquifer was still deep under the water table.

3.1.1.3 Striped Karren on Snake Mountain Above Kunming (Yunnan, China) Unique striped karren give a special landscape stamp to the extensive top of Snake Mountain above Kunming (Figs. 3.10 and 3.11). Lithomorphogenetic research reveals the manner

40

Fig. 3.10 Striped karren on Snake Mountain

Fig. 3.11 Cross section of Snake Mountain karren

M. Blatnik et al.

3

Lithomorphogenesis of Karst Surface

of the formation and development of this karren on vertical rock strata in transition from limestone to dolomite and their formation from subsoil karren to karren shaped by exposure to rainwater. The strata between limestone beds are highly diagenetically recrystallized limestone–dolosparite. The thicker and more resistant strata protrude several metres from the sediment covering the top. Rows of individual and clustered rock teeth and smaller rock pillars developed from them. The density of the vertical fissures dictates the size of the rock pillars and teeth while the distinctness of the horizontal fissures influences their shape. The pronounced tectonic action of this area caused the strata to stand upright and become vertically and horizontally fissured. This rich geological history is revealed by its cover of thick layers of fine-grained alluvial sediment. Precipitation water permeates through the sediment, corroding the rock below it and shaping subsoil teeth in the process. With the rapid washing away of the sediment, especially along the vertical bedding planes as well as along vertical and horizontal fissures, rock teeth in strips appeared on the surface and rock pillars developed from the most resistant rock. The rock forms can be classified into subsoil and rain-carved as well as composite rock forms. It also reveals the manner of formation of the entire spectrum of rock from limestone to dolomite, the diverse composition and resistance to corrosion of the rock, and the fissuring that indicates the decisive importance of lithological and tectonic characteristics in the varied formation of karren under specific conditions. Larger subsoil rock forms (Fig. 3.12)

Fig. 3.12 Subsoil funnel-like notch (Snake Mountain)

41

occur on all types of rock while smaller rock forms such as rain flutes only occur on evenly composed limestone or limestone sections of dolomitized rock (Fig. 3.13). The rock relief reveals a recent and relatively rapid denudation of the surface and formation of karren from subsoil forms, since such forms still dominate. Even before the denudation, the distinct vertical percolation of water dominated in the subsoil formation of the karst; gently sloping subsoil hollows were carved downwards that generally show no traces of paragenesis.

3.1.2 Karren Development in Mediterranean Environment Relative to conditions, the example of the Kamenjak hum also belongs here, but due to the emphasized impact of rock characteristics on the karren development, it is discussed in the next chapter.

3.1.2.1 Karren Above Custonaci (Sicily, Italy) The study area is situated in the Mt. Sparagio ridge belonging to the northern part of the Monti di Trapani relief in the north-west of Sicily. The territory is predominantly mountainous and its orographic profile is characterized by a series of ridges delimited by coastal plains. Average annual precipitation is 600 mm. The studied karren are on a slope of the Noce area (Fig. 3.14) and at the upper edge of the slope which

42

M. Blatnik et al.

Fig. 3.13 Shaping of a limestone and b dolomite (Snake Mountain)

continues to a plateau-like karst elevation. On the lower part of the slope, individual rocks and rock teeth protrude from the soil as well as larger rock outcroppings in places. They are up to 1.5 m in height and rounded or conical in shape. In the middle section there are more rock surfaces, the rock teeth are oblong and lie across the slope. The upper edge is all rock and dissected in mostly more extensive, up to 10 m or wider, rounded stone hills and somewhat smaller rock pillar with walls up to 10 m high. The studied profile displays alternating beds of calcarenite and calcirudite. All the beds are distinguished by a high content of total carbonate, with the lowest content always higher than 95% (Fig. 3.15a, b). The rock has a distinct impact on the occurrence and formation of smaller rock forms (rain flutes, rain scallops); in places, the size of grains in the rock affects the development of larger rock forms as well. Karren and smaller stone forests develop from subsoil karren. The development of the latter is evident in distinctly developed subsoil rock forms ranging from subsoil cavities that in places densely hollow the rock and traces of vertical percolation of water through the soil such as subsoil funnel-like notches and channels to longitudinal notches representing the traces of long-term levels of soil surrounding

the rock. Subsoil cups and channels form on horizontal and gently sloping areas that in places are covered by soil. Denuded rock with subsoil rock relief is transformed by rainwater and water trickling down the walls and flowing through the rock and from cavities in the walls. Sharper peaks of rock teeth that developed on thicker beds of rock are mostly subsoil forms that have been only partly transformed by rainwater. Large funnel-like notches often bear witness to this (Fig. 3.16a). We can assume the relatively young denudation of the karren or at least of their lower parts. The wider peaks are often flat. They were formed where thinner beds of rock lying above thicker ones decomposed. On such peaks, the water creeps over larger surfaces and flows over the edge to the walls. Rain flutes only occurred on individual places and are relatively indistinct forms dictated primarily by lithological characteristics. Rain scallops often dominate. A flat surface, which in this development model is first dissected by channels and funnel-like notches therefore gradually dissects into a pointed surface (Fig. 3.16b). Systems of cylindrical holes of biocorrosion, helixigenic origin give a special stamp to the rock relief of this karren (Fig. 3.17). They are a characteristic of the rock surface in the wider environment of karst development.

3

Lithomorphogenesis of Karst Surface

43

Fig. 3.14 Karren on a slope of the Noce area

Fig. 3.15 a Thin section made of rock slice seen on the b. b Blue epoxy rasin imprinted in the rock slice prepared for thin section

3.1.3 Influence of the Rock on Formation of Karren in Various Environments In addition to the stone forests, the examples of Mushroom Mountain and Snake Mountain described above also reveal the unique impact of the foundation rock on the formation of denuded subsoil karren. The next example is as the previous

one from Sicily situated in the mediterranean environment, and bears the stamp of a unique formation primarily due to the crumbling of the edges of the gently sloping rock strata and consequently the development of the rock relief first on the smooth interbed surfaces and then on the dissected rock. The thinly layered rock dictates the development of karren in Lagoa Santa (Brazil), while marbles are decisive in the

44

M. Blatnik et al.

Fig. 3.16 a Subsoil funnel-like notches reshaping by rain. b Dissection of the top of the karren in Noce area

development of karst karren with the dominance of flaking in the freezing conditions of Altai.

Fig. 3.17 Snail holes (Noce area)

3.1.3.1 Karren of the Kamenjak Hum (Dalmatian Karst, Croatia) The Kamenjak study area is situated in the coastal karst of Croatia in the immediate vicinity of Vransko jezero (Lake Vrana) (Fig. 3.18a, b). The geological structure of the wider surrounding area of Lake Vrana consists of rocks dating between the lower period of the Upper Cretaceous and the Upper Neogene, as well as younger and mostly unconsolidated Quaternary sediments. The most frequently represented limestone dates in the upper part of the Upper Cretaceous with well-pronounced stratification and average strata thickness of 20–50 cm. We studied the hum’s upper fourteen limestone strata in the SW–NE direction. From the foot to the peak the dip of the strata varies only slightly, running predominantly towards the north and ranging between 10° and 15°. Strong fissuring is visible throughout the rock. Numerous, mostly subvertical faults, fault zones, fissures and calcite veins are observed in all directions, predominantly in the E–W direction. In places the rock is bituminous. Combining the observations with the results of the complexometric titration analysis, we were able to determine the properties of the rock. Based on the thin sections, we divided the studied profile from the lithological aspect into four parts: the lower section is dominated by micrite to microsparite limestone with prevailing content of various largely micritized whole and fragmented foraminifers. The following second section of the profile is sparite limestone

3

Lithomorphogenesis of Karst Surface

45

Fig. 3.18 a Karren on the top of Kamenjak hum. b Karren of Kamenjak hum: a, b subsoil channel, c subsoil hole, d hole, e rain flutes, f shelve, g rain pits, h rain channel, i steps, j channel, k solution pan

composed almost exclusively of peloids. The lower section of the upper half of the profile is mostly micrite limestone with various mostly whole and fragmented foraminifers and peloids. The upper section of the profile is composed of alternating layers of micrite, microsparite, and sparite limestone with foraminifers and peloids. Throughout this section of the profile, the rock is very homogenous with a few tiny calcite veins (Fig. 3.19). The entire geological profile including all the strata that form the peak of the hum responds similarly to karstification. From the viewpoint of climate, the area in the immediate vicinity of Lake Vrana has a mild Mediterranean climate with average monthly air temperatures varying between 5.9 °C in January and 23.8 °C in the warmest month of July

Fig. 3.19 Typical rock composed predominantly of peloids of regular shape (pellets of faecal origin). Sample was dyed in alizarin red dye

and an annual average of 14.2 °C based on the data from the Jankolovica meteorological station. The mean annual precipitation totals around 1,000 mm, with the range of average monthly amounts between 17 mm (July) and up to 147 mm in November, the average wettest month (Magaš 1990). The area is also characterized by periodic and very intense short-term precipitations that trigger periodic torrents at the outlet. The karren that dissect the wide top of the Kamenjak hum develop on inclined rock strata. Except towards the SW where it ends with a steep slope and walls, the hum has gentle slopes (it is higher in the sketch than in nature). The slopes are distinctly dissected by karren, two-thirds of which are sometimes densely but in most cases sparsely overgrown

46

with shrub interspersed with large rock surfaces in most cases linked to the edges of rock strata. The karren are stepped (Fig. 3.20a, b) and the edges of the upper karren are several metres back from the lower ones. The surfaces of the rock steps are mostly flat, developed on larger blocks of rock strata, with only their edges able to disintegrate into medium and small size rocks. The tops of medium size rock steps in particular that are several decimetres wide tend to form into points and ridges while the smallest disintegrate into gravel. The crumbling and sliding of rock and gravel downwards is more distinct at the edges that develop in the direction of the strata’s dip although the upper edges of strata also crumble. This is primarily dictated by the density of fissures in the rock, the thickness of strata, and the spacing of the strata along the bedding planes along which the rock slides downwards.

M. Blatnik et al.

The rock relief reveals all the significant development stages from subsoil formation to dissolving and disintegration of the upper rock strata as well as denuding and reshaping of newly uncovered rock surfaces. There are steps on denuded flat surfaces (Fig. 3.20c, d), traces of creeping sheets of water and solution pans. Only their upper edges and the walls of the ledges are dissected by rain flutes. Over time, the walls of steps and solution pans also become dissected by flutes. As a rule, the edges of strata have crumbled into numerous smaller rocks. These are sharp and dissected by flutes. The traces of subsoil formation are only preserved in the lower belts of karren. The karren gradually become three-dimensionally dissected. Flat surfaces where steps, traces of creeping water, dominate become dissected surfaces where rain flutes and channels are the most characteristic rock forms (Fig. 3.20d) in the upper part (see Sect. 3.3).

Fig. 3.20 a The edge of the karren with flat top on Kamenjak Hum. b The edge of the karren with pointed tops. c Flat and pointed tops with typical rock features. d Flat top with typical rock features (steps, solution pans, rain flutes)

3

Lithomorphogenesis of Karst Surface

3.1.3.2 Subcutaneous Stone Forest on Breccia (Trebnje, Central Slovenia) The subcutaneous stone forest has been discovered during the motorway construction and represents the first phenomenon of this type in Slovenia. Individual columns (Fig. 3.21a) attain the height of up to 8 m. Prior to the building interventions this stone forest has not been revealed on the surface, since there were only peaks of columns that were protruding for several metres out of the thick soil, which could at first sight be considered and classified as smaller karren. The Trebnje area is composed of Triassic and Jurassic shallow marine carbonate rocks, in places overlain by up to few metres thick Pliocene–Quaternary deposits and soil

47

(Pleničar and Premru 1977). Scattered erosional patches of the Late Cretaceous deeper marine marl and sandy deposits disconformably overlay Triassic and Jurassic carbonate successions. In the outcrop at Trebnje, a host rock is composed of two lithologies, light grey massive internally stratified dolomitized limestone and grey coarse-grained dolomitic breccia which occupies a major part of the outcrop. Locally, the upper part of the pinnacles beneath the soil is slightly silicified. The breccia (Fig. 3.21b, c), which is laterally discordant to approximately 30° SW declining stratified dolomitized limestone, is internally disorganized, with chaotic clast orientation and no apparent internal stratification. Fabrics include both matrix- and clast-supported styles,

Fig. 3.21 a Subsoil stone forest in the Trebnje area. b Breccia stone pillar. c Breccia. d Uncovering of the subsoil stone forest in the Trebnje area

48

M. Blatnik et al.

commonly in close proximity. Breccia clast size is variable, yet it typically ranges from very fine pebble to boulder; coarse pebble to cobble size seems to be the most common. Gravel sorting is poor. Clast shape is variable but slightly elongated forms are most common. Roundness is very low, with most clasts being angular, however, especially smaller ones could be also sub-angular. Despite spatially limited outcrop and the lack of information from the adjacent areas, described features yield enough information to interpret the chaotic breccia as synsedimentary, fault, fissure or small graben related, tectonically influenced phenomenon, deposited as gravitational rock fall and/or mass flow deposit which was formed during changing conditions in the formerly relatively monotonous part of the Late Triassic (Early Jurassic?) shallow marine carbonate platform. Regarding their shape, the columns may be divided into two types. The predominant are those large-sized. In their lower part, they occupy up to several square metres large area. They are further carved out in the forms of subterraneous rocky features. They were formed out of larger massive bulks of rock, which were not markedly or thickly fissured. Pinnacles of such pillars are bladelike and have several sides and they are further carved in the form of the funnel-like incisions (karren), beneath which there are large subcutaneous runnels. The second type of the columns is represented by individual (Fig. 3.21d), pointed and less bulky structures. The most pronounced rocky features, which are carved into the columns are the funnel-like incisions (karren) and subcutaneous flutelets. The diameter of funnel-like incisions at the top of larger columns extends from 10 cm up to 2 m,

they are of semi-spherical shapes and for the most part represent the orifices (inlets) to the subsoil runnels (flutelets). The rock surface may be distinguished between the surface that was positioned below the soil and the other one, which was formed above on the soil. The upper part of the former is a carved boxwork, which as it seems, occurs due to the faster washing away of the solution, whereas the latter, the lower part, is weathered up to several centimetres deep, it is soft and is rapidly disintegrating (Fig. 3.21b). The most markedly weathered is the surface of the subcutaneous slits (karren). The surface of the rock, which was located above the ground, is well washed away, yet, as it is also typical of this type of rock, it is also characteristically “dolomitically” carved. It is interlaced with a mesh of slits which extend along the calcite veins.

Fig. 3.22 a Karren under vegetation (Lagoa Santa, Brazil). b Karren on laminated rock: a subsoils channel, b subsoil cup, c network of tubes along contact, d subsoil cup or kamenitza, e rain flutes, f notches along

contacts, g vertical jaggedness, h half-funnel-shaped notch at the end of channels, i channel from the inter-laminae tube, j ceiling pocket, k pits

3.1.3.3 Karren on Laminar Calcarenitic Rock of Lagoa Santa (Minas Gerais, Brazil) The karst area (Fig. 3.22a, b) developed on a plateau with altitudes that vary from 650 to 900 m. The karst plateau is covered with a thick pedological cover and its main features include dolines, uvalas, poljes, outcrops and caves. The poljes and uvalas often flood to become temporary lakes. A variety of karren can be identified on the outcrops. This study was done at the outcrop surrounding the Lapinha Cave in Sumidouro State Park. According to Berbert-Born (2000), the average temperature in the area in July is around 23 °C, with a median minimum of around 11.2 °C. From October to March, the average temperature is around 29.6 °C. The average annual precipitation is around 1,380 mm. The dry period extends

3

Lithomorphogenesis of Karst Surface

for about five months from May through September with less than 7% of the annual precipitation, characteristic of a typical tropical precipitation regime with a great concentration of rain in summer and drier winters (Patrus 1996). Cerrado (Brazilian Savannah), semideciduous seasonal forest and deciduous seasonal forest are the main types of vegetation in the region (IBGE 1993). The dark grey to black rock (N2 to N5, Rock-Colour Chart) gives a macroscopic impression of homogenous finely laminated and only slightly fissured carbonate rock in a predominantly horizontal position. Despite the often strongly expressed homogeneity where single laminae are barely visible on the karstified surface, we can also observe less homogenous sections laterally that are only apparent as the consequence of long-term exposure to the atmosphere and precipitation. The alizarin colourant dyed the entire thin section red, which almost entirely proves the presence of calcite only. The mineral grains in the rock are arranged in a predominantly horizontal direction in alternating micrite, sparite and microsparite laminae or sections. Micrite laminae or sections, which change laterally and horizontally in thickness and the size of mineral grains, dominate in some parts of the rock, and sparite laminae dominate in other parts. Compared to sparite laminae, micrite laminae display a more uniform parallel course and only occasionally wedge out laterally. Sparite laminae, on the other hand, in most cases display a very uneven course, “jumping” into one another in a vertical direction, wedging out, varying greatly in thickness, often appearing as pseudocalcite veins, and the like. The sample is carbonate rock with an almost 100% proportion of total carbonate. The two per cent of dolomite shown by the calcimetric analysis is found in the form of individual hypidiomorphic grains inside thicker (400– 900 µm) sparite laminae. The outcrop of carbonate rock (Kohler 1989; Berbert-Born 2000) with vertical and overhanging walls towers several dozen metres above the surrounding impermeable surface (Fig. 3.22a). The top of the outcrop is horizontal or stepped, formed along the more or less horizontal contacts in carbonate rock. They are crisscrossed by vertical fissures along which cracks developed that are frequently overgrown. At the foot of the hollowed carbonate rock, a network of periodically flooded foot caves of smaller diameters developed (Travassos and Kohler 2009, 288). Above them rise overhanging walls, originally shaped at the contact with the sediments that surrounded the limestone outcrop and today transformed by characteristic traces of three-dimensional karren formation. The central section of the limestone mass is perforated by old caves that reflect the periods when the limestone was surrounded by impermeable rock to a higher level and the caves were often filled with

49

fine-grained sediments, which is evident from the dominance of above-sediment rock forms. Currently, the upper part of the outcrop is being transformed three-dimensionally largely by the precipitation that falls on its top and percolates vertically through the rock along fissures, flows through tubes along the contacts in the rock, and creeps and trickles down the walls. The partial overgrowth of trees and shrubbery has a further significant effect. To a great extent, the form of the karren is dictated by the laminated beds with horizontal plane lamination and by its fissuring. Thin-layered karren that form on the surface as a rule have flat tops while subsoil karren are pointed (Knez et al. 2011a, b). Tubes (Figs. 3.22b and 3.23) developed along the contacts through which water flows periodically and shapes the walls below them. Ceiling pockets occur below fissures in overhanging walls (Figs. 3.22b and 3.24), and water dripping from fissures hollows out pits. The tops covered by vegetation are dissected by networks of subsoil channels (Figs. 3.22a and 3.25) filled with weathered debris that developed from inter-laminae tubes when the upper laminae of the rock dissolved. Exposed parts of the tops with flutes, rain pits and solution pans are being reshaped by rainwater.

3.1.3.4 Selected Karst Karren on Marbles with Characteristic Rock Relief and Scaly Splitting of the Rock (Altai Republic, Russian Federation) In our studies of karst phenomena, a research was undertaken in the south of the Altai Republic in the Gorno-Altaysk region in southern Siberia (Figs. 3.26, 3.27a–c, 3.28a–d and 3.29a–d). The area is part of the Central Asian Orogenic Belt of the circum-Pacific type. As a reaction to Late Neoproterozoic to Paleoproterozoic subduction-accretion and collisional events between the Asian and Indian plates, an accretion complex, metamorphic rocks of high PT and intermediate bands of ophiolites were formed. Characteristic tectonic structures are overthrusts and slip faults (Ota et al. 2007). An examination of the microscopic properties of the investigated rocks reveals the main causes for the pattern of their karstification and disintegration. Lithologically they belong to regionally metamorphosed carbonate rock. Their parent rocks were pure limestone, impure cherty limestone and limestone that was interlayered and/or laminated with silty and marly layers (flysch like?). The basalt dike indicates volcanic activity in the region, which could suggest an impact of slight thermal overprint. The effect of dynamometamorphism is evident in all investigated samples. Their structural characteristics and the internal structure, lithological characteristics and mineral composition of the parent rocks played the most important role in their deformation and hence

50 Fig. 3.23 Bedding-plane tubes, wall channels, rain flutes (Lagoa Santa)

Fig. 3.24 Ceiling pockets due to water percolation (Lagoa Santa)

M. Blatnik et al.

3

Lithomorphogenesis of Karst Surface

51

Fig. 3.25 Subsoil channels (Lagoa Santa)

in their sensitivity to different ways of weathering, karstification and disintegration. Progressive recrystallization of the rock was followed by ductile to semi-ductile deformations. The calcite grains reflect the impact of cataclasis and mylonitization under direct stress at considerable depths. The rock has a scaly splitting that follows the oriented structure and cleavage planes. A local slight folding of the rock can be observed in the field that caused interbedding differential slips and slips along cleavage planes. The developed weakened zones contribute to the more rapid disintegration of the rock. In the case of brittle deformation, the purer marbles are competent rock and were therefore strongly affected by fracturing on the macro and micro levels. This is most evident in the coarser grained (saccharoid) marble layers. Microscopic and sub-microscopic intergranular porosity developed, enabling the capillary suction of water and therefore strong hygroscopicity and the sensitivity of the rock to the freeze-thaw effect. As a result, the marble rapidly disintegrates to sandy and platy pieces. The rock relief reveals similar conditions of the formation of all three described karren. The subsoil formation of the rock and its transformation by rainwater that reaches the rock directly and carves rain flutes (Fig. 3.28c) and rain pits or creeps down the rock or through it carving channels and

co-forming pits, one of the most characteristic forms of these karren, play a visible role here. The water also hollows the rock. The pits (Fig. 3.28c) are a composite rock form. In their formation, rainwater, creeping and standing water, biocorrosion, and subsoil formation beneath material brought in by water make their marks in various ratios. On rock that has been denuded for a longer period, the latter forms can dominate and this is usually so on sunless parts of the rock. Scaly splitting of the rock imprints the most distinct stamp on the rock relief. Over time, the traces of rock formation described above can alternate between the dominant chemical dissolving and scaly splitting or mechanical disintegration. The variety of scaly splitting is mostly determined by the properties of the layered or grained metamorphosed carbonate rock. This was also established by Ollier (1984, 15, 18) who gave examples of scaly splitting as a consequence of the impact of temperature change on intergranular and fissured porous and moist rock and the freezing of moisture. Due to the metamorphosing, the carbonate rock has the same properties in this case. All three cases are unique. The inclination of the most distinct splitting layers also has an important influence on the shape of the karren.

52

M. Blatnik et al.

Fig. 3.26 Locations of researched karren in Altai Republic

In the Ak-Kaya valley (Fig. 3.27a–c) the manner of splitting is dictated by the vertical thin-layered composition of the recrystallized rock. The scales are several centimetres thick, usually dissect the wall in a step-like manner, and accumulate beneath it. The water flows along cleavage surfaces in the rock and perforates it with smaller tubes that are denuded in the process of disintegration. The disintegration is dictated by the fine perforation of the thin-layered rock and apparently by the freezing of water in the cavities. A characteristic example of scaly splitting of thickly layered rock is revealed in the sunny walls of Ak-Bom (Fig. 3.28a–d). The scales vary in size from square

centimetres to several square metres and are relatively thin. In places where scales fall off, steps occur. Parts of the rock that protrude from the walls split the most distinctly, and therefore the walls are evenly rounded. At the confluence of the Katun and Chuya rivers (Fig. 3.29a–d), the rock splits along cleavage surfaces where the lower parts of the slope of the valley was formed. The layers are a few decimetres thick. Interlayer cavities form into which water brings sediment and flowstone is deposited on the ceiling above it. Due to the increasing volume and the freezing of moist sediment in them, the upper layer swells and bursts and its pieces slide down the slope.

3

Lithomorphogenesis of Karst Surface

53

Fig. 3.27 a Stone pillars in the Ak-Kaya valley. b Rock relief of a stone pillar: a subsoil cups and channels, b rain flutes, c bedding plane channels, d steps, e pits, f subsoil half-bell, g wall channel, h wall channel below shelf, i ceiling cup, j rain scallops. c Wall channels

3.1.4 Mountain Karren in Tibet Characteristics of the formation of mountain karren on the surface uncovered from under the southernmost glacier in the northern hemisphere and in the southern part of the Tibetan high plateau are clearly visible in northern Yunnan.

3.1.4.1 Mountain Karren in Northwestern Yunnan, China The mountain karren rock relief, the Yulong Snow Mountain limestone pavements above Lijiang (Fig. 3.30a, b) and the plateau-like Shika Snow Mountain above Shangri-La (Fig. 3.30a, c), reveals the manner of the formation of the

mountain karst surface in NW part of Yunnan at altitudes 4,000–4,600 m. The Yulong Snow Mountain (5,596 m) is part of the mountain chain that surrounds the high Tibetan plateau in the southeast. The Yangtze River acts as a border between the two. The plateau-like Shika Snow Mountain (4,449 m) above Shangri-La lies in SE part of the Tibetan plateau. The first mountain receives 500 mm of precipitation and the second something above 617 mm in the form of snow and rain. On the southern slope of Yulong Snow Mountain karren with distinctive rock relief formed below the conical peaks along the gently sloping section beside the glacier with the southernmost location in the northern hemisphere.

54

M. Blatnik et al.

Fig. 3.28 a Ak-Bom walls and karren. b Rock relief: a funnel-like notch, b subsoil notch, c subsoils cups, d steps, e cups, f pits, g rain flutes, h rain pits, i solution pan, j wall channel. c Cups and rain pits and

flutes. d Calcite marble with sheets of chlorite along foliation and in the transverse micro-fractures. Parallel polarizers

Given the geomorphology of the basin in the area of the city of Lijiang, the depression is considered to be of the so-called pull-apart origin. At the contacts of branched left lateral faults in particular, the original relief has been completely changed by karst processes. This is also an important contact between Permian basalts and Triassic limestones and clastic rocks. The wider area of the central part of the Yulong Snow Mountain is composed mostly of Carboniferous grey limestone, oolitic limestone with chert nodules, conglomerates and marble. In places we also observed dolomitized limestone. The broad peak of the plateau-like Shika Snow Mountain (Fig. 3.30c) is dissected into numerous rounded peaks. The highest peaks tower several hundred metres high, and some have steep walls. Between them are large dolines and oblong dells. The wider area of the mountain peak is composed of Middle Triassic grey limestone and dolomite limestone of the Shanglan group. The lithological group of Shanglan rock

is 2,500 m thick and its lower part is composed of dark grey limestone and marly limestone. Microcrystalline schists and slates occur laterally. Two dominant factors, snow and rain, decisively influence the formation of the majority of rock forms; in places, particularly on the Shika Snow Mountain, two additional factors are subsoil corrosion and water trickling from overgrown surfaces. The dominance of one of the factors causes the formation of more or less uniform sub-snow or rain rock forms; other factors affect the rock to a lesser degree. Composed rock forms display traces of several factors that alternate or follow one another as in the case of denuded subsoil forms. The channels below snow covered (Fig. 3.31a) or overgrown ledges are the trace of water trickling down the walls from the ledges, rainwater falling directly on them, and, in the lower parts, long-term snow cover. Sub-snow rock forms dominate in places where the rock has been covered by snow for a longer period (Fig. 3.31b). These are primarily the gently sloping sunless parts of the

3

Lithomorphogenesis of Karst Surface

55

Fig. 3.29 a Wall karren in the valley of the Chuya River. b Karren rock relief: a hollow below rock scales, b subsoil cup, c solution pan, d channels, e rain flutes, f rain pits, g pits, h channels with cups, i steps.

c Scaly splitting. d Marble with p intergranular porosity among ca calcite (stained red) grains. Parallel polarizers

karren, the lower parts or lower walls of karren, and fissures. Gently sloping sunless parts of the karren are often dissected in various ways so there are sub-snow forms on their lower parts and rock forms carved by rainwater on the higher parts, peaks and ridges. Rain rock forms dominate on sunny surfaces and parts of the rock that are steep, located higher above the floor and covered by only a thin layer of snow. Frequently, the same surface displays rain rock forms typical of steep walls and sub-snow rock forms typical of gently sloping parts of the rock side by side. The relief and individual rock forms are also influenced by fissuring and recrystallization of rock characteristic of the Shika Snow Mountain. The rock masses on the Yulong Snow Mountain are larger and its rock forms have more regular shapes. On the Shika Snow Mountain, rock recrystallization has an important influence on rock forms, causing fine diversities and often jagged edges of rock forms.

The relatively low latitude and its characteristic climate conditions therefore prevail over the high altitude, which at higher latitudes is characterized mostly by sub-glacier and subsoil rock relief (Kunaver 2009; Tóth 2007, 2009).

3.1.5 Karren Under Tropical Vegetation Thick vegetation on karren also dictates the particularities of their formation.

3.1.5.1 Felo Pérez Mogote (Viñales, Pinar Del Rio, Cuba) The Felo Pérez mogote (Fig. 3.32a, b) is located in the Viñales Valley, a karst polje developed between the Sierra de los Organos mountain range and the hills of Pizarras del Sur in Pinar del Rio province and is known for its typical

56

M. Blatnik et al.

Fig. 3.30 a Location of researched karren in northern Yunnan. b Karren beside glacier. c Karren on the top of plateau

surface karst landforms and its large caves. In the case of the Felo Pérez mogote, the rocks belong to the Tumbadero Member, one of the members of the Guasasa Formation which consists of micritic limestones and sandstones. Throughout the studied geological column the rock is very uniform. Micritic limestone (mudstone) dominates and in most cases it is heavily tectonically crushed. Recrystallized whole and particle fossil remains were found in only two layers. Stylolites were identified in the majority of the taken samples. With use of the complexometric titration method, it was established that the total carbonate in all the samples from the profile exceeds 96.5%. All the samples also contain

a significant amount of dolomite and insoluble residue. The beds in the entire geological profile that compose the mogote responded in a similar way to karstification. Rock composition enables clear development of rock features, the smallest, as well. The original subsoil development of the mogote reveals a relatively dense system of subsoil hollows. The rocky surface of the mogote is also of subsoil origin. Subsoil rock forms are most distinctly preserved at the lower edge of the mogote that is surrounded by periodically flooded alluvium and in the notches on the slopes where the sediment remained the longest. In the upper section that has been

3

Lithomorphogenesis of Karst Surface

57

Fig. 3.31 a Wall channels. b Under-snow steps (Yunnan)

Fig. 3.32 a Mogote with karren. b Rock relief on mogote karren: a subsoil hollow, b subsoil notch, c subsoil half-bell, d subsoil cups, e funnel-shaped notch, f rain flutes, g channels, flutes, scallops due to water creeping, h wall channels

denuded the longest, characteristic rock forms were shaped by rainwater. They cover the subsoil rock relief and in places intertwine with it (Fig. 3.33a). Under the dense vegetation that covers the karren and whose remains are deposited on it, the rock is being reshaped in a unique manner. Its entire surface is dissected by cups (Fig. 3.33b) that formed under the weathered debris. In summary, we can trace the gradual denudation of the mogote and the reshaping of the rock relief from subsoil forms to those attributed to rainwater on the longest denuded and only sporadically overgrown surfaces at the top and to those on the lower section of the gentler slopes that form under thick vegetation. The latter give the rock relief a most distinctive and special seal characteristic of this type of rock formation.

3.1.6 Karren in an Arid Area 3.1.6.1 Karst in Ras al-Khaimah (Northern United Arab Emirates) Several locations in Musandam Mountains have been explored for caves, karst springs and surface karst features. Surface rock relief resulted from different karst processes was studied in river beds and side walls of wadis and on the mountain plateaus. Potholes, sub-sediment pockets and sub-sediment channels are the dominant forms found in rocky riverbeds and on rocks in smaller wadis. In places, potholes located at the edge of the rock grew into tubes one metre or more in diameter. Tubes 1–2 m in length and from a few tens of centimetres to one metre or more in diameter are also found

58

M. Blatnik et al.

Fig. 3.33 a Rain flutes and subsoil cups. b Subsoil cups (Mogote)

in the walls. They could be seen as the beginning of characteristic caves. Only the lowest parts of the riverbed are usually smoothed by erosion, while sub-sediment pockets and sub-sediment flutes (Fig. 3.34) are found higher up, the traces of a periodically flooded riverbed. Large pockets (Fig. 3.35) on the walls of the wadis are one of their most characteristic forms. In places they dissect the majority of rocky wadi slopes, elsewhere their larger part, or only individual sections, in short, anywhere they have not been transformed due to the decomposition of the rock or shaped by rapid water flows in the river beds. The pockets are found on vertical, inclined and overhanging surfaces. Their diameter and depth are measured in metres. They are either single or composite. Some of the pockets display dominant characteristic forms indicating their formation along sediment. As a rule, the lower sections of their circumferences are more or less horizontal while the upper parts are semi-circular or narrow towards the top. On the tops or on the walls there are straight or winding channels that most probably formed due to the water flowing at the contact with sediment. Their bottom sections are usually open. Large pockets are dominated by the paragenetic formation of ceiling pockets in the locally flooded zone. The water constantly fills them with sediment that makes them widen and grow upwards (Slabe 1995a, b). With the lowering of the water level that permeates the sediment, the water flows downwards along the walls, often opening the pockets in the process. This indicates that when the pockets are denuded the rock weathers at a faster rate and they are therefore shaped or transformed by the “cavernous weathering process” (Goudie 2009). In shallow circular pockets with a distinctive thin outer edge, this process, accelerated by various salts present in the rock, wind and microclimatic characteristics in the pocket (Goudie 2009), could be the dominant one. The rock surface of the majority pockets displays fine weathering. Is this how the large or deep

pockets formed? Does this mean the faster weathering of the rock in the upper part and the deposit of weathered debris in the bottom part resulting in the asymmetrical shape of the pockets? Can we speak about tafoni in all such cases? In some pockets, a honeycomb of tiny holes developed on the upper edge that could be the consequence of the rapid disintegration of the rock due to “evaporate cooling of the saline solution in the cavity” (Rodríguez-Navarro et al. 1999; Goudie 2009) or they could have developed at the contact with sediment as in caves. In the wadi Haqil, pockets are found at the end of smaller caves filled with sediment or they reach the size of smaller caves themselves. All the walls in the wadi caves display clear traces of long-term filling with sediment. Hunt (1996) and Goudie (2009) explain such pockets on Malta as originally subsoil in character and later transformed by “subaerial weathering processes”. At this stage we can conclude that these are mostly composite rock forms with traces of frequent dominance by one of the factors of their formation, along-sediment factors being the most distinctive. These are important questions, because these forms are characteristic of this karst and give it a distinctive and unique appearance. Rocks in the sediment also display sub-sediment channels up to one metre in diameter. They are shaped by water that flows from the surface of the sediment and percolates downwards along the contact with the rock. There are also shallow along-sediment notches at the sediment level. Subsoil cups and subsoil channels developed on rock that was covered by soil or sediment to a large degree or only in places (Slabe and Liu 2009). On horizontal or slightly inclined surfaces denuded pockets are transformed into shallow solution pans. On denuded bare rock there are microrills (Fig. 3.36) that are mainly characteristic of relatively recently denuded rock surfaces and as a rule are the first and most frequent rock forms on such surfaces. They are found on the slightly

3

Lithomorphogenesis of Karst Surface

59

Fig. 3.34 Sub-sediment flutes (Ras al-Khaimah)

Fig. 3.35 Large pockets on the wadi slopes (Ras al-Khaimah)

inclined surfaces of wadi slopes, on the rocks on their bottoms, and on the karren between wadis. They are composed of small cups linked in a linear fashion (Gómez-Pujol and Fornos 2009). They are carved by thin film of capillary-guided moisture that crumbles the rock. The film of water or rain then removes pieces of the rock (Gómez-Pujol and Fornos 2009, 83). They are periodically flooded by water that appears to deposit thin-grained sediment in them. Larger rocks display networks of rain flutes and rain pits as well as microrills on the surface between them, that is, on the

sections of the rock that were covered by sediment or soil for a longer period.

3.1.7 Sea Karren 3.1.7.1 Lithology, Rock Relief and Karstification of Minamidaito Island (Japan) Minamidaito Island (Fig. 3.37) is located on the Philippine plate. The island lies about 360 km SE of Okinawa Island.

60

This island is shifting towards the Ryukyu subduction zone at a speed of about 4–5 cm/year. Topographically, the outer ring of the higher parts with limestone walls has an average elevation of 40–75.1 m a.s.l. The lower part of the ring has a basin-like form with doline lakes. The water table of the doline lakes is at 2 m a.s.l. The caves in the higher land areas developed vertically with many speleothems. Caves are also found in the lowlands. The speleothems are distributed below the water table, indicating that the caves were formed during a lower sea level period under a cold climate. There were three karstification periods on Minamidaito Island. The first karstification occurred during the Pliocene between the lower and the upper Daito Layer. The top surface of the lower Daito Layer was karstified and soils were formed. During the Pleistocene, karstification continued from 1.6 Ma until the last glacial period. The terrain of Minamidaito Island, which resembles an uplifted atoll, continued to karstify until the middle of the last glacial period when the sea level dropped by 100 m. Since then karstification similar as today is taking place. During the Holocene, the sea level rose. Numerous rock samples from different parts of Minamidaito Island were studied in detail and subjected to calcimetric analyses. Coral biointrasparite limestone (framestone and bafflestone with transitions to grainstone) and coral dolomitized biointrasparite limestone (framestone and bafflestone) with around 75% dolomite in the total carbonate content were identified (Fig. 3.38). The calcimetric analyses showed that the distribution of limestone and dolomite in individual locations differed from that previously described

Fig. 3.36 Microrills on denuded bare rock (Ras al-Khaimah)

M. Blatnik et al.

(Ohde and Kitano 1982). There are different models of dolomitization. Suzuki et al. (2006) believe that the dolomite on nearby Kitadaito Island was formed through seawater dolomitization during the glacial lower sea level, which is the most frequent explanation for dolomitization on atolls. We assume that Minamidaito Island experienced similar geological and environmental conditions. The described carbonates are a typical example of carbonate sediments of a shallow coastal belt; therefore, the sedimentation environment of the profile near Kaigunbo and other areas are ranked as the area of reef environment. Although the characteristics of coral limestone and dolomitized limestone put a distinctive stamp on the rock relief, it remains an important trace of the formation and development of this unique karst landscape. The rock is often heavily perforated in three dimensions during the subsoil phase, when the subsoil formation is followed by denudation, and ultimately when it suffers corrosion due to seawater spray. The rocky circumference of caves is subject to decomposition. The rock is relatively smooth only in places hollowed by the erosive and corrosive action of waves (Figs. 3.39a, b, 3.40a–c) and subsoil processes (Fig. 3.39a); rock exposed only to rain is less dissected than that exposed to seawater spray as well (Fig. 3.40b). The unique features of the rocky shoreline are dictated by the erosive power of the sea, especially during periodic typhoons. This periodic character is evident in the dominant proportion of features created by the corrosive activities of seawater (Figs. 3.39b, 3.40c), biocorrosion, and biocrust and the state of erosion forms found several metres inland, on

3

Lithomorphogenesis of Karst Surface

61

Fig. 3.37 Minamidaito Island

shore platforms, or in walls (Fig. 3.40a, c). The surface of the interior of the island was formed under the soil; only the denuded sections of karren are transformed by rain.

3.2

Shilin Stone Forests (Yunnan, China), a UNESCO World Heritage Site

Stone forests are a unique karst surface landform and a unique form of pinnacle karst (Fig. 3.41). It took more than 200 million years for the Shilin stone forests (Yunnan province, China) to develop. Tectonic shifts have slightly furrowed and fractured the carbonate block of rock in the area of the present-day Shilin, creating a vertical network of fissures. The Shilin stone forests began to form under thick beds of sediment from subsoil karren and are today one of the most spectacular examples of humid tropical to subtropical karst. Erosion has caused the sediment above the young karst to thin and the limestone is becoming increasingly exposed to the atmosphere and weathering. Water is dissolving the rock along the primarily vertical fissures and faults. The favourable climate conditions and lithological structure are creating deep karren. In other words, the water is dissolving the more compact rock between vertical fissures and faults more slowly. That is why there, between the vertical fissures and faults, stone pillars up to tens of metres high are being formed or preserved (Fig. 3.42). Depending on the different composition of the moderately undulating and predominantly horizontal rock beds, the stone pillars are of various shapes, from conical to mushroom-shaped.

Because of the exceptional characteristics of this karst phenomenon in China, we propose the term “shilin”, meaning a stone forest, to be used for this type of surface landform in the professional literature. The extensive stone forests composed of many pillars, several metres or several tens of metres high, provide karstologists with a unique insight into the formation of karst landscape and are an international tourist attraction. The area of stone forests covers roughly 500 km2 and is located in Shilin Yi Autonomous County, Yunnan province, near Shilin, approximately 90 km from the provincial capital Kunming. The Shilin National Scenic Area is classified as an AAAAA-level Scenic Attraction, a National Geo Park, a World Geo Park, a National Key Scenic Area, and a World Natural Heritage Site accepted by UNESCO in 2007 (Fig. 3.43). It has been known since the Ming Dynasty as the “First Wonder of the World” and is today visited by 5 million visitors yearly. The development of stone forests has been presented many times (Yuan 1991; Sweeting 1995; Ford et al. 1996, 1997; Song and Wang 1997; Knez and Slabe 2007), and their forms have been described even more often (Chen et al. 1983; Song 1986; Maire et al. 1991; Song and Liu 1992; Hantoon 1997; Salomon 1997; Song and Li 1997; Yuan 1997; Yu and Yang 1997; Zhang et al. 1997a, b; Gabrovšek et al. 1998; Knez and Slabe 2001a, 2002; Song and Liang 2009; Knez et al. 2011a, b, 2012). Increasing emphasis is being placed on the study of anthropogenic influences on the karst landscape and on its protection (Kranjc and Liu 2001). The development of caves under the stone forests and their

62

Fig. 3.38 Coral rock (Minamidaito Island)

Fig. 3.39 a Coastal karren. b Rock relief of coastal karren. Legend: a sea notch, b small sea pans, c surface etched by sea spray, d large pans formed by corrosion and erosion, e sea pans formed by sea spray,

M. Blatnik et al.

influence on the formation of the forests have also been examined (Šebela et al. 2001). The formation of stone forests and their rock relief are the result of the way the rock was formed and of the characteristic weathering processes on various carbonate rocks. The interdependence of the stratification, fissuring and composition of the bedrock with various processes in the formation of the karst landscape under diverse conditions is important. The prevailing process of carbonate rock formation is their dissolution under different conditions and under the influence of different factors. In the case of the formation of stone forests the most important process is the dissolution of rock below the sediment and soil and the denudation of rock due to rainwater, but also below vegetation. Organic substances in the soil with increased levels of organic carbon (Slabe 1995a, b; Urushibara-Yoshino and Miotke 1999) accelerate the dissolution of carbonate rocks. We, the researchers of the ZRC SAZU Karst Research Institute, are the only ones who have been conducting continuous research of the stone forests in the area of Shilin since 1995 (Knez 1997, 1998a, b; Gabrovšek et al. 1998; Kogovšek and Liu 1999, 2000; Kogovšek et al. 1999; Knez and Slabe 2001a, b, 2006a, b, 2007, 2009, 2013; Kranjc and Liu 2001; Šebela et al. 2001, 2004; Slabe and Liu 2009; Knez et al. 1997a, b, 2011a, b, 2012, 2017). On this occasion, we are presenting our most important findings. As researchers of the Karst Research Institute, we were also involved in the inscription of stone forests on UNESCO’s World Heritage List. In 2018, at the invitation of the Shilin management, we set up a permanent exhibition on our research into stone forests in the area of the administrative

f erosional cave, g subsoil surface, h by sea spray and rain etched and partly disintegrated rocky ridge (Minamidaito Island)

3

Lithomorphogenesis of Karst Surface

63

Fig. 3.40 a Traces of the erosion action of the sea water. b Sea notch. c Sea pans (Minamidaito Island)

building that also contains a museum which provides a thorough scientific explanation of the formation of stone forests.

3.2.1 Different Types of Karst in Yunnan Province Under various climatic and geological conditions, three different types of karst have formed: tropical rain forest karst in the south, tectonic depression karst and high plateau karst with stone forests (Song and Liu 1992; Zhang et al. 1997a, b). A vast area of tropical rain forest karst stretches in the Xishuangbanna area, southern Yunnan. Two karst areas

stand out: the Mengla province, an area covering around 500 km2, and the 450 km2 of territory along the Lancang River. In the Mengla province, the carbonate layers deposit is over 2,000 m thick. Under the influence of the humid tropical climate, the limestone underwent intensive karst processes. The characteristics of the karst landscape along the Lancang River are reflected in the numerous depressions and blind valleys where stone teeth, as well as individual stone pillars, are quite frequent. Karst in tectonic depressions is a very widespread occurrence in the wider central Yunnan area, where there are at least 28 isolated parts, none of which is less than 100 km2 in size. The largest is the so-called Kunming basin, exceeding an area of 1,100 km2 and with a catchment area of

64

Fig. 3.41 One of the Shilin stone forests

Fig. 3.42 Forming of a stone forest along vertical fissures and faults

M. Blatnik et al.

3

Lithomorphogenesis of Karst Surface

65

Fig. 3.43 The Shilin National Scenic Area, classified as an AAAAA-level Scenic Attraction

over 3,000 km2. The loose rock cover in Kunming basin is approximately 1,000 m thick. Stone forests indicate a specific type of a high plateau karst landscape with characteristic groups of standing limestone pillars reaching a height of over 50 m. Limestone pillars usually stand on a gently wavy base. An extensive and diverse system of water courses has developed under the forests. The form and height of the pillars in the forest depend on the individual type of rock and their topographical position.

3.2.2 Development and Shaping of Karst Karren and History of Shilin Stone Forests Research The Shilin stone forests are a unique form of karst karren (Knez et al. 1997a, b; Gabrovšek et al. 1998; Knez and Slabe 2001a, b, 2002, 2006a, 2007, 2013; Knez et al. 2011a, b). The karren, which is crisscrossed by fissures along the fractures, is composed of rock teeth (Fig. 3.44) and rock pillars (Fig. 3.45). The pillars are 5–50 m high and are of various shapes. Large stone forests are a characteristic

feature of subtropical climate conditions (Habič 1980; Song 1986; Song and Liu 1992). Based on their location, Song (1986) distinguishes three types of stone forests: valley, hilltop and hillslope. In lowlands and valleys, large stone forests occur with intermediate dolines and depressions. Underground waters flow beneath them, which means that they are periodically flooded or that water flows through them. The stone forests on hill tops are lower, 10–30 m high, their pillars grow from a common foundation, and the cover of sediment above them is thin. The stone forests on hillslopes are an intermediate form between the other two types. The Shilin stone forests are often described as a form of covered karst (Chen et al. 1983; Maire et al. 1991; Sweeting 1995; Slabe and Liu 2009). The carbonate rock, on which karren have developed, was covered by thick layers of sediment that decisively influenced the occurrence and shape of the stone forest. Based on the thickness of the sediment, a stone forest can be barren, covered or buried. Hantoon (1997) describes stone forests as an epikarst form. Mangin (1997) believes that the epikarst of the stone forests extends to a depth of 100 m.

66

The Shilin stone forests were formed predominantly through dissolving of rock below soil and sediments. Water increased the width of the fissures and separated rocks. Under the sediment with acidic water, wide and deep cracks developed between pillars with deep channels on their walls (Yuan 1997). Uncovered carbonate rock is transformed by rainwater. Teeth develop first and from them, the forests form (Song 1986). Originally, limestone, which was already undergoing the process of karstification (Yu and Yang 1997; Song and Wang 1997), was covered by Permian basalt and tuff that influenced its shaping and in places metamorphosed the rock (Song and Li 1997; Ford et al. 1996). Water permeated through basalt and tuff, and underground karst began to develop. In the Mesozoic, part of the limestone was exposed (Song and Wang 1997). In the Oligocene and Miocene, rock blocks rose and lowered, while in the lower parts the karst relief was transformed by erosion (Yu and Yang 1997). In the Eocene, the Lunan graben subsided and thick layers of lake sediments were deposited (Chen et al. 1983; Zhang et al. 1997a; Song and Wang 1997). In the tropical climate,

Fig. 3.44 Rock teeth

M. Blatnik et al.

thick layers of laterite soil developed on the sediment (Sweeting 1995; Ford et al. 1997). In the Pliocene, the current stone forests began to develop (Yu and Yang 1997). In the Quaternary, a great part of the sediment was removed but some still remained in the fissures. The underground water level played an important role in development of stone forests (Ford et al. 1997). With the development of underground watercourses, pillars began to develop from teeth (Zhang et al. 1997a). The fluctuating underground water widened the fissures (Yuan 1991). Today there is an extensive and diverse system of water caves below the forests (Zhang et al. 1997a). Tectonic action resulted in lowering of the underground water level, removal of sediments from the surface and in more rapid growth of stone forests. Numerous examples of stone forests that have developed under almost identical conditions confirm that diverse shapes of pillars are primarily the consequence of distribution and density of joints and fissures that cut the carbonate rock and of rock’s varying stratification and texture. We must also stress the importance of efficiency of their formation as

3

Lithomorphogenesis of Karst Surface

67

Fig. 3.45 A rock pillar

influenced by underground factors, and their reshaping by rainwater that determined the course of their development in different periods (Gabrovšek et al. 1998; Knez et al. 2011a, b). Stone forests are found not only in South China but also elsewhere throughout the world. In Madagascar they are called tsingy, and in the Philippines assegai (Salomon 2009). In Sarawak there are unique and up to 100 m tall Mulu stone forests (Day and Waltham 2009) which are perhaps the largest and among the best known. In Papua New Guinea there are the Mount Kaijende stone forests (Williams 2009), with pillars up to 100 m in height. Stone forests (Salomon 2009) also dissect the surface in Cameroon, Congo (Kouilou), Kenya, Tanzania, Brazil (Bom Jesus da Lapa), Thailand (Ta Khli), Northern Australia (Chillagoe, West Kimberley, Gregory Karst; Salomon 2009; Grimes 2009)

and Spain (El Torcal; Narbona 1989). Unique stone forests on calcareous aeolianites are also found in the Nambung National Park in Western Australia (Ford and Williams 1989). Similarly shaped karst features (Fig. 3.46) were discovered during motorway construction works that artificially exposed the low and covered karst of the Dolenjska region in Slovenia (Knez et al. 2004).

3.2.3 Lithological and Morphological Characteristics of Shilin Stone Forests More or less horizontal layers of the rock of various thickness and composition are crisscrossed by vertical fissures or cracks. Each of these features can have an important influence on formation of the network of stone pillars in a forest, on

68

Fig. 3.46 Covered karst of the Dolenjska region in Slovenia

their size and shape, and consequently on the rock relief. They interact in various combinations, fostering a vast diversity of stone forests. However, as a rule, one of the features of the rock or one of the factors of their shaping is dominant. Exposed subsoil karren is reshaped by rainwater. The lengthy development of stone forests has allowed creation of large karst forms. Due to the development of caves beneath the forests and the erosion of alluvium and soil that previously covered the carbonate rock, exposure takes place faster than dissolving of the rock by rainwater.

3.2.3.1 Lithology and Its Impact on a Shape of Stone Pillars The area of stone forests is composed of Lower Permian carbonates of the Qixia and Maokou formations. These formations are two of the more important basal formations on which numerous stone forests have developed. Characteristics of the Qixia formation are micrite limestone with intercalations of dolomite and dolomitic limestone with intermediate sheets of schist. In the lower part of the Maokou formation, limestone alternates with dolomite and dolomitic

M. Blatnik et al.

limestone (Figs. 3.47, 3.48 and 3.49). In the upper part, we trace the sequence of limestone, which is thinly bedded in places and elsewhere composed of several-metre-thick beds, as well as massive limestone, which in individual horizons contains up to several decimetres of thick quartz chert nodules. The main lithological features of the Maokou formation are roughly similar to the Qixia formation, the only difference being that in the Maokou carbonates we have not traced any major impact of late diagenetic dolomitization and in some places there is considerable secondary porosity. In both formations, we notice heavy diagenetic variability of the rock which is undoubtedly the consequence of the intensive volcanic (basalt lava) activity during transition from the Palaeozoic to the Mesozoic. The rock has an exceptionally high percentage of carbonate. What is macroscopically most noticeable in the geological profiles is different thickness of layers which varies from ten centimetres to many metres; according to some data, even more than 30 m (Song 1986). In stone forests, we encounter rock sequences composed of several-metre-thick homogeneous and compact layers where karstification is advancing considerably faster on tops, along bedding planes and individual fissures, and below the surface, as well as sequences of thin-layered limestone (10 cm and more) where intensive karstification is already accelerating along numerous lithological contacts. In geological profiles we find an alternation of thickly- and thinly-stratified carbonate as well. Where layers are thinner, pillars may be much thinner due to more rapid corrosion. In some places we encounter thicker segments of very porous layers where the intercrystal porosity exceeds 20% in most cases. They are characterized by dolosparite and dolomicrosparite of the grainstone type. The light brown and in some places extremely pure and almost completely transparent dolomite grains reach a diameter of one millimetre while their average diameter is one-third of a millimetre. In contrast to the homogeneous and compact rock, a segment of the porous layers does not karstify merely along the lithotectonic contacts but across the whole profile in accordance with the stage of porosity. The rate of karstification of such rock is substantially greater and additionally accelerated locally below the surface. Late diagenetic dolomitization is also typical of some layers. Where increased porosity and dolomitization appear in the same layers, more intensive karstification is found as well. A special example is dolomitization of individual smaller fields in such a way that otherwise homogeneous, compact and impermeable rock becomes freckled. Dolomitized limestone is therefore less influenced by karstification than pure thickly-stratified limestone. To a lesser degree, we see that dolomite fields, usually with a diameter of a few centimetres, protrude from the rock.

3

Lithomorphogenesis of Karst Surface

69

Fig. 3.47 Shilin stone forest, limestone, Lower Permian, Maokou formation

Fig. 3.48 Shilin stone forest, dolomitic limestone, Lower Permian, Maokou formation

3.2.3.2 Rock Composition and Its Impact on a Shape of Stone Pillars Numerous examples of stone forests that have developed under almost identical conditions show that diverse shapes of forests and pillars are primarily a consequence of

properties of the rock. In the same stone forest which has developed on diversely composed rock, pillars may be of various but typical shapes, a consequence of their development at different levels of a diverse rock column. However, we must also consider significance of the impact of

70

M. Blatnik et al.

Fig. 3.49 Shilin stone forest, dolomitic limestone, Lower Permian, Maokou formation

subsoil factors on their shaping and transformation by rainwater, that is, the course of their development in various periods.

3.2.3.3 Fissuring of the Rock and Its Impact on a Shape of a Stone Forest and Size of Stone Pillars Morphological characteristics are reflection of various factors. One of them is fissuring of the rock, which influences a shape of the forest and dimensions of stone pillars. distribution of the pillars (ground plan of the stone forests) matches fracturedness of the rock. Pillars may be joined in rows between distinct joint sections and stand closely side by side, or stone forests or their parts may be composed of individual wide or narrow pillars. As a rule, pillars with smaller diameters occur along dense networks of fissures, while larger rock masses with broader tops occur along thinner networks. 3.2.3.4 Stratification of Rock and Its Impact on a Shape of Stone Pillars An especially important factor is stratification of rock, which affects the shape of stone pillars. Beds have virtually no impact on pillars that have developed on thicker beds and beds with an even rock texture. However, vertical cross sections of pillars on thin beds of rock are often jagged because they are dissected by notches that occur along bedding planes, and unequal resistance of different beds of rock is reflected in their external shape.

3.2.3.5 Rock Texture and Its Impact on a Shape of Stone Pillars Rock texture, especially if it is diverse, can decisively influence shaping of stone pillars, that is, a shape of their vertical cross sections and the size of cross sections. Porous beds are often hollowed and disintegrate faster, while beds of rock with less soluble components most often protrude from walls. 3.2.3.6 Subsoil Processes and Their Impact on a Shape of Stone Forests, Rainwater Sharpening of Rock and Rock Relief A unique development of stone forests is reflected in their rock relief. Rainwater sharpens tops of pillars and transforms traces of their original subsoil formation. Subsoil and composed rock forms, especially the largest ones, are the most distinctive. Subsoil rock forms include scallops, large channels, notches, and half-bells and subsoil channels and cups on broader tops, while composed rock forms include channels leading from subsoil channels or solution cups, which dissect walls of pillars. Many pillars are subsoil undercut, and their tops have been transformed by secondary subsoil rock forms and shapes hollowed by rainwater. A unique rock relief is found on larger rock pillars, especially on those that have wide tops, either on thick beds of rock where secondary subsoil rock forms occur or on tops that have developed due to disintegration of thin rock beds, where subsoil tubes that occurred along bedding planes have been transformed into subsoil forms or large channels reshaped by rainwater. Both

3

Lithomorphogenesis of Karst Surface

features also indirectly influence shaping of pillar sides due to flowing of water and hollowing of channels. As a rule, smaller rock forms do not occur on dolomite rock, on very porous rock, or on rock with large inclusions. Subsoil forms develop on a relatively permeable contact between rock and sediment. Subsoil cups develop under soil which only partly covers the rock due to water percolating through the soil and flowing along the contact with the rock. The most porous, largely dolomite, strata are relatively densely perforated with subsoil tubes. Above-sediment channels are a result of water flowing over the sediment when hollows were filled with sediment. Floor channels develop when the hollows empty as the level of the sediment surrounding the pillars drops. Composite rock forms are distinctive. These are larger channels on the lower parts of the pillar walls. Smaller, but of similar origin, are vertical channels that lead from subsoil tubes. Notches and half-bells occur where long-lasting layers of soil and sediment surround the pillars. Rock forms shaped by rainwater are most distinct on the tops of the walls of stone pillars; they include flutes, channels, cups, and solution pans. They often develop on old subsoil rock forms, reshaping them or creating composite rock forms together with the factors that shape subsoil rock forms.

3.2.4 Selected Examples of Stone Forests 3.2.4.1 Major Stone Forest The Major Stone Forest (Figs. 3.50 and 3.51) is a typical and referential example of development of karren from subsoil into a stone forest exposed to rain and vegetation. Research has provided a basic description of its lithomorphogenesis and development, and represents a basis for further study and understanding of different types of stone forests. A central part of Major Stone Forest superbly reveals main characteristics of the formation of various stone forests distributed over an area of 350 km2. A relatively thick stratification and evenly composed rock clearly show a development of stone forests from subsoil karren. This is evident in a shape of individual parts of the stone forest and in a shape and rock relief of pillars that comprise the forest. The central part of the forest is located in a valley at 1625–1875 m a.s.l. Most (70–80%) of the annual 936 mm of rain falls between June and October. After abundant precipitation, the water table, which is normally just below the surface, rises by 10 m. The average temperature is 16.3 °C and oscillates between −2 ºC and 39 °C. As regards structure and texture, the carbonate rock in the Major Stone Forest, which spreads across an area of 11 km2, is relatively uniform, with exception of a few shorter sections. The rock is thickly stratified and contains numerous stylolites, and bedding planes are mostly clearly expressed

71

and widened by corrosion on the outer side of the rock (Knez 1996). Research studies indicate that the 260-million-year-old Lower Permian rock (Maokou formation) was heavily diagenetically altered. Although undamaged by tectonic action, fossil remains are mostly unidentifiable. The dip of the strata, which is mostly around 5° and seldom larger than 10°, indicates minor regional shifts. Pillars are up to 35 m high. In the central part they usually stand close to each other and cracks between them are usually 1–5 m wide, while in the wider surrounding areas solitary pillars are also common. They are remains of carbonate rock between fissures and are shaped accordingly. Their cross sections are square and triangular, as well as oblong and narrow. The dense fissuring of the rock has resulted in smaller cross sections of pillars. The pillars composed of thinner and fissured strata in their lower sections are mushroom-like and as a rule have conical tops at the same level. The pillars that were undercut below the soil have relatively horizontal tops that are somewhat blockier with larger surface areas. The pillars are also dissected along bedding planes and along long-lasting layers of sediment and soil. The notches along bedding planes are often jagged, which reflects the stylolithization of the rock. Conical and blade-like pillars with sharp tops and ridges are predominant. Geologic studies of the rock in the Major Stone Forest have established that the type of rock is clearly reflected in the intensity of corrosion and erosion and through it in the formation and morphological appearance of individual stone pillars and larger blocks of rock. The even composition and thick stratification of the rock enables the full development of forms, which show how this type of stone forest is shaped. The rock relief on the pillars in stone forests reveals interwoven traces of original shaping of the rock below the soil and sediment, of lowering of the level of soil and sediment, and of the younger but distinct transformation of pillars by rainwater, which naturally dominates on the tops.

3.2.4.2 Naigu Stone Forest Naigu Stone Forest (Figs. 3.52 and 3.53) stretches along two slightly uplifted tectonic ridges. Faults bordering the fault zone are very strong, and intermediate faults, mostly running in the NW–SE direction, are several kilometres in length and very deep. Pillars were formed in a carbonate formation more than 100 m thick. Naigu Stone Forest lies 20 km east of the Major Stone Forest and is an important tourist attraction. Pillars which include 20–30 m tall tower-like rock masses and smaller pillars stand side by side or separately. Their shapes reflect lithological properties of the rock and their evolution. The mushroom-shaped pillars are the most frequent. Tops of the

72

M. Blatnik et al.

Fig. 3.50 Sketch of the Major Stone Forest

pillars that have merged into more extensive towers are located at a uniform level and have several short, conical peaks. Naigu Stone Forest is composed of carbonates of the Lower Permian Qixia formation. The most important characteristics of the Qixia formation are a strong diagenetic change in the basic rock, dolomitization, and, in some places, considerable secondary porosity and a high percentage of carbonate. The geological profile of rock properties indicates great diversity. We have traced changes in colour, bedding, porosity, inclusions and other characteristics. The feet of the lowest exposed part of the Naigu Stone Forest are composed of massive and homogenous carbonate. The rocks that come up in the geological profile are less resistant to corrosion and erosion. They form a narrower part of pillars below a wider and consequently much more resistant upper part. In this part, the primary limestone is heavily late-diagenetically dolomitized. In some places density of dolomitized sections changes laterally as well as vertically. The secondary intergranular porosity may change laterally but in general it is estimated at 5–10%. The possibility of subsoil corrosion of the rock is great, mostly due to considerable porosity and poorly cemented dolomite crystals. Massive dolomitized limestone is typical of the upper part and is characteristically rough and striped with protrusions

of dolomite sections. Due to their convex shape on the surface of the rock, their more pronounced roughness, and their consequently heavier lichen cover, the dolomite sections are of a dark grey colour; on the surface of the rock they appear as dark grey to black stripes on a light-coloured base. The size of pillars is mainly a consequence of faults and fissures that vertically crisscross the beds and of effectiveness of the subsoil dissolution of the rock along them. The network is diverse; the stone forest is thus composed of larger rock masses and smaller pillars that stand either close to one another or are isolated. Pillars developed at different levels of the beds of rock, which is reflected in their shape. Mushroom-shaped pillars are the most typical, and distinctive notches have developed in the middle part of the pillar. This is the consequence of more rapid subsoil corrosion and hollowing of this part of the rock, which is the most porous and decomposes the fastest on the surface. The middle parts of the pillars are therefore narrower. The mushroom shape, which is characteristic of the larger pillars, is naturally less distinct in the narrower pillars. Subsoil and composite rock relief forms are the most distinct. Subsoil rock relief forms include large channels, overhanging undercuts of pillars, and subsoil channels on the wider tops. The channels running from subsoil channels

3

Lithomorphogenesis of Karst Surface

Fig. 3.51 Major Stone Forest

or subsoil cups are composite rock relief forms. The deepening of subsoil cups and the discharge of water down the channels is caused by the dissection of the tops of the pillars, especially the larger ones, into cones with funnel-shaped notches between them. The traces of the development of the Baiyun Cave in the central part of the stone forest testify to the forest’s gradual and diverse development, which is, of course, linked to the development of the caves underneath it. The cave’s sediments and its rock relief reveal many periods in the development of the cave in the epiphreatic part of the aquifer, as well as the rapid lowering of the groundwater level, which probably caused the faster “growth” of the stone forest.

3.2.4.3 Lao Hei Gin Stone Forest Lao Hei Gin Stone Forest (Figs. 3.54 and 3.55) lies 20 km north of the Major Stone Forest. Individual stone pillars and larger rock blocks shaped by corrosion and erosion cover only about 2 km2. Larger groups of stone pillars consist of several tens of pillars. Between them there are corroded fissures or narrow

73

passages. Smaller groups of pillars, composed of ten or fewer pillars, are most often cut only by cracks and corroded fissures. Over a relatively large area of the stone forest we find only individual pillars and stone teeth. Individual pillars are relatively large, broad and high, or low and wide. The bedding is reflected in the form of pillars mainly because of the diverse rock composition. The pillars are either solitary or in groups within which there are only cracks and fissures. They were formed at various levels on nearly horizontal rock beds and in corresponding shapes. The exposed lower part of the geological profile or stone pillar is composed of fully dolomitized limestone, the middle part is composed of porous dolomite, and the upper parts of the stone pillars are composed of more durable limestone and dolomitic limestone, resistant to erosion. The beds in the middle part of the pillar decay and decompose faster, below and above the soil, and since they are generally covered by more durable strata, the pillars form characteristic mushroom-like shapes. The pillars are wider below the narrower parts if the lower dolomite strata are exposed. The rock relief consists of various groups of rock forms: subsoil, those carved by rainfall and combined forms. Their characteristics are defined by the composition of the various rock beds. The tops are sharp and highly segmented around the cracks. This is characteristic of all the forms carved by rainfall―namely channelled rock forms and solution pans. Their surface is notably coarse. On limestone beds that occur only in some of the highest-lying parts of the stone forest, the flutes and small channels are evenly shaped. On porous and faster-disintegrating beds, there are no distinct rock formations carved by rainfall, except at the beginning of the exposed rock, which is covered by more rounded parts of the subsoil rock relief. These have formed distinctly on all types of rock beds. Their surface is mildly coarse.

3.2.4.4 Pu Chao Chun Stone Forest Pu Chao Chun Stone Forest (Figs. 3.56 and 3.57) is a minor stone forest 15 km south of the Major Stone Forest. Rock pillars are situated on a ridge, where their layout is the densest, and on the slope below it. Pu Chao Chun Stone Forest consists of Lower Permian carbonates of the Maokou formation. The formation is one of the more important base formations from which numerous stone forests in the Shilin region have developed. The lower part of the rock sequence consists of thick-bedded to massive limestone, while the upper part consists of beds of limestone several tens of centimetres thick. Both are tectonically deformed with numerous subvertical faults running in various directions. Lithostratigraphically, they are genetically connected, with no stratigraphic gaps between them. They also indicate a similar depositional environment. Diagenetic influences through

74

M. Blatnik et al.

Fig. 3.52 Sketch of the Naigu Stone Forest

their geological history are evenly expressed across the entire profile. In the lower part of the profile, limestone contains numerous bioclasts and is micritic to microsparitic. Only exceptionally there are calcite veins in the rock. There is no trace of secondary porosity. The rock of such characteristics allows development of subsoil rock forms, as well as features carved by rainfall. Up in the geological profile are beds of the upper part with layers 10–50 cm thick. All thin-layered beds are equally resistant to corrosion and erosion. They form the narrower part of the pillar above the wider and much more resistant part. In terms of shape, rock pillars can be divided into two types, defined mainly by stratification of the rock from which they were formed. In the upper part of the stone forest the characteristic shape of the pillars is a result of thin rock beds. The upper parts of the pillars are relatively narrow. Well-expressed notches and subsoil holes have formed in the contact zone. The lower parts of the pillars are stout and made from a single thick rock bed. The narrower rock pillars are the narrowest where the strata are the thinnest. The pillars are oblong, due to the cracked rock. The tips of the pillars are relatively level where the top beds of the rock

were thin and had swiftly disintegrated. Only the thicker beds of rock have become tapered and are marked by funnels and rock formations carved out by rainwater. In the lower part of the stone forest, which has developed in the thick rock beds, the rock pillars are of a more even shape: stout at the bottom, if they were not thinned by the subsoil karstification, and tapered towards the top, with relatively sharp tips. Distinct subsoil features, holes and features on the rock surface have also formed between the beds of this type. All the rock features, which reflect the genesis of the stone forest, are well developed. The subsoil rock features are large subsoil channels on the rock faces and subsoil channels and cups on the larger tops. The combined rock features are channels that lead from the subsoil channels and cups located on the tops, and subsoil holes between the bedding-planes. The exposed subsoil rock features are reshaped by rainwater which hollows flutes, channels and scallops.

3.2.4.5 Shui Jing Po Stone Forest In lithomorphogenesis, the rock and its relief show typical characteristics of a rapid development of the stone forest (Figs. 3.58, 3.59 and 3.60) from subsoil karren on the top of

3

Lithomorphogenesis of Karst Surface

75

Fig. 3.53 Naigu Stone Forest

cones and ridges between them, and a slower development on the slopes beneath. The stone forest was formed in biomicrite and biomicrosparite carbonate beds with an extremely homogeneous composition. The beds are composed of biogenic and non-biogenic carbonate grains of predominantly the same size that occupy more than 90% of the volume of the rock and have a very high total carbonate content. The dissolving method (Engelhardt et al. 1964) was applied in complexometric analyses; it was established that all samples from the profile reached 100% total carbonate. The largest groups of the tallest stone pillars developed on wide, rounded peaks and on ridges between them, i.e. on the tops of hills dissected by an extensive stone forest. The stone pillars often vary in height with individual pillars standing out distinctly. Mostly individual stone pillars are also found lower down on the slopes. The latter are shorter as a rule. Only individual narrow belts and rarely larger areas of the stone forest, which are generally taller, are densely

packed. Narrower stone pillars dominate in all parts of the stone forest, and only individual larger rock masses are found between them. This form was dictated by a relatively dense network of vertical fissures along which subsoil cracks had already developed. The taller pillars reach 15 m in height while most are lower; only the tallest pillars, which are rare, stand several metres high. The beds of rock differ in thickness, and the tops of the stone pillars formed on thin beds are distinctly dissected and jagged. The caps of individual pillars stand on narrow bases. They are composed of a more durable rock bed and are consequently wider. At the tops of the rounded hills, the stone pillars have been relatively thoroughly transformed by rainwater. The relief at the top of them has been distinctly transformed or has developed into the forms that occur due to rainwater and water trickling down the walls. Their lower sections, however, have still preserved subsoil rock forms, mainly subsoil hollows. The rock relief is impossible to be seen on the

76

M. Blatnik et al.

Fig. 3.54 Sketch of the Lao Hei Gin Stone Forest

densely fractured rock, which is dissected by numerous notches across a large surface and is not infrequently densely perforated. The tops of the stone pillars formed on such rock are especially diversely dissected. On the rock that was covered by vegetation, usually by creepers or dense scrubs, there are present small oblong notches about 1 cm in diameter. These can measure several decimetres in length and be connected in networks. They cover the tops and large surfaces or just the belts on walls. Biocorrosion is also active below the lichen covering the rock in thin layers and is particularly distinct in hollows. It primarily influences the fine dissection of the rock. Despite the occasional slight macroscopic differences in the rock where we took the samples, it turned out that the composition of the rock is very even, homogeneous, and uniform throughout the entire thickness of the studied geological column. Through the macroscopic and microscopic studies, this unchanging composition has confirmed that the karstification of the beds comprising the studied profile took place at the same rate.

The stone forest and its rock relief have been distinctly transformed mainly in the areas of larger stone pillars on the rounded peaks and the ridges between them, which reflects their long-term denudation. A characteristic of the formation of the uncovered subsoil rock forms are the traces of the relatively rapid and recent denudation of this part of the stone forest. Subsoil rock relief dominates in the stone forest and on the stone teeth on the slopes.

3.2.4.6 Subsoil Stone Forest Revealed During Earthworks for New Kunming Airport An interdisciplinary approach was utilized to demonstrate a need for holistic karstological studies prior to performing extensive works in a karst environment in the area of the location for the new Kunming airport. The study included research of the surface karst features and microscopic analyses of rock samples, hydrogeological studies and microbiological analyses of two karst drinking water sources in its vicinity. The results show specific characteristics of a subsoil stone forest, indicating a high level of karstification.

3

Lithomorphogenesis of Karst Surface

Fig. 3.55 Lao Hei Gin Stone Forest

Fig. 3.56 Sketch of the Pu Chao Chun Stone Forest

77

78

M. Blatnik et al.

Fig. 3.57 Pu Chao Chun Stone Forest

The surface of the hilly area was dissected by low, up to one metre high or sometimes slightly higher, and relatively sparse karren with pointed and stumpy rock peaks. They were separated by larger or smaller patches of sediment covered by soil and shrubs or trees. The earthworks revealed a subsoil stone forest (Figs. 3.61 and 3.62) covering almost the entire area of carbonate rock that boasts unique characteristics of form dictated largely by composition of the rock. The karren that dissected the surface was the top of the subsoil stone forest. The rock is fractured by subvertical faults 5–10 m apart. Faults generally run in the N–S and E–W directions. Karst processes have denuded the rock laterally along the faults many metres in width and up to ten metres deep. Today, larger rock masses or stone pillars have remained only where the fault network is less dense. Dissection of the rock surface, dictated by composition of the rock with relatively large dolomite lenses, left a special mark on the subsoil stone forest. The lenses are about 20 cm in diameter and up to several cm3 in volume. The textural characteristics of solid and homogenous limestone dominate the entire area.

Stratification is almost never observed in the solid and homogenous rock, however, in individual places largely horizontal contacts between rock segments can be seen. Important general characteristics of the rock are a strong diagenetic change in limestone: recrystallization, dolomitization, and, in some places, considerable secondary porosity and a high percentage of carbonate. Relatively large stone pillars dominate in the subsoil stone forest. Their lower sections are five or more metres in diameter. As a rule, pillars end in a number of conical peaks, and some pillars have wide tops dissected below the soil. The pillars measure up to 10 m in height. The larger, often elliptical cross sections of the pillars and differences in their size reflect a sparser and unsymmetrical network of fissures that vertically cut the carbonate rock and widen below the soil between the pillars. The rock relief clearly shows a subsoil formation of stone pillars below the soil and sediment that cover the carbonate rock and transformation of denuded tops. The most distinct rock forms are subsoil channels that dissect the walls and tops of the pillars. The vertical channels frequently have extensive funnel-like mouths at the top and measure 1 m or

3

Lithomorphogenesis of Karst Surface

79

Fig. 3.58 Sketch of the Shui Jing Po Stone Forest

more in diameter; however, smaller and more or less horizontal channels wind only between the peaks. Subsoil cups have also formed in the latter. From the surface, water creeps through the channels along the contact of the sediment and soil with the rock. A characteristic rock relief dissects tops of the pillars that were denuded and exposed to rain. The rock forms include rain flutes, rain pits, solution pans and scallops that have formed due to the creeping of water down the overhanging surface of the wall. The rain flutes could form only on the limestone rock between nodules of dolomite. As a rule, solution pans developed from subsoil cups when the tops of the pillars were denuded. The surface of the rock surrounded by soil is similar since just below the soil, where dissolution is most pronounced due to the organic matter in the soil, water erodes grains of dolomite rock at a faster rate along a permeable contact. The nodules protrude semispherically most distinctly from the walls that are deeper below the surface. The contact between the rock and sediment is poorly permeable and therefore the saturated water drains away at a

slower rate. This is also evident in the weathered layer of the rock. Individual sparry calcite grains protrude from all surfaces. Below the stone forest, there is a well-developed network of caves through which watercourses flow and carry away the sediment washed from the surface by rainwater, enabling their growth despite the poor permeability of the contact between the rock and the sediment.

3.2.5 Stone Forests and Their Development Numerous examples of stone forests that have developed under almost identical conditions confirm that diverse shapes of pillars are primarily a consequence of the rock characteristics, distribution and density of faults and fissures that cut the rock and their varying stratification to composition (Fig. 3.63). However, we must also consider the significance of the impact of subsoil factors on their shaping and transformation by rainwater, i.e. the course of their development in various periods.

80

M. Blatnik et al.

level, which is a result of the rapid disintegration of the thin beds. Porous beds are often subsoil hollowed and disintegrate faster on the surface, which is why the pillars alongside them are narrower and the shapes of the tops on such rock are not typical. The more resistant beds of rock protrude from the cross section. The tops of the narrower pillars are sharp; they are sharpened by subsoil factors and rainwater. A unique rock relief is formed when the rock is shaped below the soil. The development of stone forests and the rate of their growth in a given period are also influenced by the location and development of the karst hollows underneath them, or by how the water flows from the karst surface, taking the sediment and soil with it. The various periods of development can be discerned from the karst hollows.

3.3

Fig. 3.59 Shui Jing Po Stone Forest

The stone forests in the area of Shilin have formed in Lower Permian carbonates of the Qixia and Maokou formations. They are characterized by a frequent alternation of very pure limestones, dolomitic limestones and dolomites, by alternation of thin and thick beds, and in some places distinct late diagenetic dolomitization and secondary porosity. The beds are mostly horizontal or dipped at an angle of 5°–10°. Due to the lively tectonic action, they are crisscrossed by numerous vertical and subvertical faults and fissures. The diverse fracturedness, stratification and composition of the rock are reflected in the shape of the stone forests and stone pillars. In the same stone forest, which has developed on diversely composed rock, pillars may be of various but typical shapes—a consequence of their development at different levels of a diverse rock column. The shape of the stone pillars, made up of thicker and evenly composed beds of rock, reflects primarily the development from subsoil karren into a stone forest; the traces of subsoil processes are gradually reshaped by rainwater. The cross sections of the stone pillars on thin beds of rock are often jagged and their tops, even those of the narrower pillars which are generally conical, are most often

Rock Relief of Karst Features Simulation with Plaster of Paris Modelling

The experimental modelling of rock features in plaster helps reveal a manner of their formation, development of individual rock features in nature, and their connections in rock relief. It also helps us distinguish the proportion and significance of the legacy of various factors that participated in the formation of rock relief and indirectly therefore the various periods of its development. Limitations do exist regarding either the size of the models or the more rapid solubility of plaster compared to carbonate rock. Primarily, we can follow the manner of the shaping of soluble stone in various conditions and the development of the rock relief on it; however, the direct comparison of individual rock features on plaster and on rock is more difficult, especially due to their size. As a rule, features on plaster are smaller (Slabe 1995b, 82). Industrial plaster (CaSo4  2 water) is used in the experiments. In one litre of water, 2.5 g of gypsum are dissolved at 20° C (Klimchouk 2000, 160). The chapter presents the latest findings of experiments in the formation of subsoil rock relief and plaster blocks exposed to rain and plaster cave tube that is wider at the flow inlet than at the outlet end.

3.3.1 Previous Experiments Described in the Literature Pluhar and Ford (1970) studied formation of flutes (rillenkarren) using hydrochloric acid on a dolomite block. Glew (1976) and Glew and Ford (1980) studied flutes with experiments exposing plaster surfaces inclined from 22.5° to 60° to artificial rain. They determined that flutes developed

3

Lithomorphogenesis of Karst Surface

81

Fig. 3.60 Shui Jing Po Stone Forest

where the layer of water flowing off an inclined surface was thin and did not prevent the direct impact of raindrops on the rock. Under a thicker layer of water, however, a smooth rock surface developed. Dzulynski et al. (1988) used modelling to study the formation of karren, exposing a fissured piece of plaster to artificial rain. They studied karren shaped by rainwater as well as subsoil karren. Experiments with plaster have been employed in researching cave rock features as well. Scallops were studied by Rudnicki (1960), Curl (1966), Goodchild and Ford (1971) and Allen (1972). Such experiments helped Quinif (1973) explain the formation of ceiling pockets, Ewers (1966, 1972, 1982) studied the development of the network of original watercourses through rock, and Lauritzen (1981) studied above-sediment channels. Tućan (1911) exposed limestone and dolomite to hydrochloric and nitric acid and established that their surfaces were similar as on the karst surface, of course with characteristic differences between limestone and dolomite. Trudgill (1985, 38) described the smoothing of rock surfaces due to exposure to acidic waters. Experimental research

(Slabe 1995a, b) on cave above-sediment ceiling channels and anastomoses, below-sediment flutes, various types of scallops and the influence of rock and hydraulic conditions on their size and shape, and ceiling pockets that occurred due to the percolation of water through fissures helped a great deal in conceptualizing their development and the diverse formation of karst caves. Some of the previous results have already been presented in detail (Slabe 2005, 2009; Slabe et al. 2016); here we add new findings acquired with new models. Mathematical and computer modelling opens up new possibilities (Perne and Gabrovšek 2009).

3.3.2 Subsoil Rock Relief For the earlier experiments (Slabe 2009, 47), a plaster block was sliced into pillars with square cross sections and sides measuring 6 cm and a height of 30 cm (Fig. 3.64). The pillars (see Sect. 3.2.3) were placed closely side by side in a

82

M. Blatnik et al.

Fig. 3.61 Stone forest revealed during earthworks for New Kunming Airport

large bucket and covered with soil. Holes were drilled in the bottom of the bucket and lastly the bucket was filled with water. The water began to percolate through the soil and run out through the holes at the bottom of the bucket. The upper two-thirds of pillar walls were corroded by tiny features, the traces of the water percolating through the sediment and its flow along the contact between plaster and sediment. The entire surface of the upper sections of the pillars was finely corroded by small cups up to 2 cm in diameter, although most are smaller. They are the consequence of water percolating constantly through the most permeable layer of soil. The larger cups, typically found in the middle sections of the pillars, display relatively smooth surfaces. On rock, of course on a much larger scale, this type of hollow is called a “subsoil scallop” (see Sect. 3.1.1.1; Slabe 1998, 55). Along the fissures or other weak spots in the rock, individual

deeper semicircular or channel-shaped hollows often occur that in time can develop into subsoil tubes. Channels with diameters 1–3 cm are formed on the walls of the lower sections of the columns. The locally saturated zone, which developed because the quantity of water flowing along the contact was greater than the quantity that could flow out of the perforated bottom of the bucket, reached as far as the upper level of the channels. This border is often marked by notches. On the lower surfaces of the pillars, even those cut in half horizontally, there are distinct networks of above-sediment anastomoses. The angularity and square cross sections of the pillars were preserved throughout their entire height. The characteristically pointed shape of the upper sections of the pillars is the consequence of the dispersed percolation of water through the soil that covered the plaster. In the latest experiment, larger plaster pillars (the largest was 20 cm long and 16 cm wide, smaller ones 12 cm long and 8 cm

3

Lithomorphogenesis of Karst Surface

83

Fig. 3.62 Sketch of the stone forest revealed during earthworks for New Kunming Airport

wide; all were 30 cm in height; Fig. 3.65) were covered with a finer fine-grained clay less permeable for water. Thus the contact between the clay and the rock was also less permeable. Subsoil shafts were the first to form between the pillars. As parts of the shafts, vertical subsoil channels with funnel-like mouths at their tops were formed on the upper sections of the pillar walls. The diameter of these features reached 3 cm. Along the less permeable contact between the plaster and the clay the water seeks the most permeable routes and merges together in flows. This was confirmed by bubbles on the surface of the water that revealed a number of distinct ponors. A special type of a channel such as described in the experiment above was formed on the lower section of the pillars in the locally saturated zone. Anastomoses were formed on the lower surface of the pillars. The tops of the pillars gradually sharpened and approached the shape of a point. Higher on

the pillar walls than in the first experiments there are horizontal or variously inclined wall notches reflecting the more complete filling of fissures and the tighter contact between plaster and clay and consequently the lower permeability of the model. In many places the surface of the plaster was weathered, indicating that the soluble material had not been simultaneously removed everywhere.

3.3.3 Rock Relief Carved by Rain In the identification of this type of formation, laboratory modelling with plaster and artificial rain is of great help (Slabe 2005). In the first stage of modelling we exposed to the rain plaster plates inclined by 27°, 36° and 63°. The first forms to appear and remain for a longer period in the centre of a thick

84

M. Blatnik et al.

Fig. 3.63 Typical shapes of pillars in the Shilin Stone Forest

Fig. 3.64 Laboratory modelling of a forest on Plaster of Paris

plaster block inclined at 36° and exposed to artificial rain after ten hours were vertical, narrow, long, and shallow scallop-like cups, while narrow channels grew on the bottom section and the top edge became rounded and dissected by semicircular notches below which rain flutes started to develop. Over time, three distinct sections took shape on the block (Fig. 3.66). The upper section was covered by flutes, the middle section was relatively flat, and channels started to grow on the bottom section. This is the characteristic shape

Fig. 3.65 Development of a pillar on plaster

of a block as presented in a book by Ford and Williams (1989, 383, 385). For the moment one could believe that the traces of the characteristic formation of inclined rock surfaces found on the upper section of the block are the consequence of the direct impact of raindrops while thicker layers of water in the smooth middle section prevent direct

3

Lithomorphogenesis of Karst Surface

85

Fig. 3.67 Long term to the rain exposed plaster

Fig. 3.66 Typical relief of inclined surface carved by rain

contact of raindrops with the rock and the channels on the bottom section occur where water flowing down the block concentrates in streams. Flutes grew slowly from the top edge downward and deepened. On steeper surfaces, the flutes are longer and also somewhat narrower. On the bottom sections of the inclined plates (27°, 36°, 63°), individual channels developed (Hortonian-type runnels; Ford and Williams 1989, 383). Between them there were larger flat surfaces. Initially, the channels mainly deepened. The ridges between them started to be transformed by rainwater which first rounded them and opened the channels and then gradually began to sharpen them. In the middle section where the block was initially smooth, channels were formed due to the water converging from the flutes while the channels on the bottom section of the block grew from the bottom up more distinctly. On the steep block (63°), however, the channels remained small, the largest reaching a diameter of 0.5 cm at most, and continued up to the flutes. Will the channels cover the smooth centre of the block completely and merge with the flutes in the upper section? What will the final form look like?

On the Karst Institute’s roof, the models were then exposed for ten years to natural rain and winter snow, 1,400– 1,500 mm of precipitation per year. On the gently sloping and moderately inclined surfaces, cups were developed several centimetres deep and protuberances were formed on the edges between them that are more distinct in the upper section of the inclined surface. On the inclined surface, they line up in the direction of the inclination (Fig. 3.67). On the steep side surfaces, channels dominate throughout. Drops of natural rain are larger and flutes carved by them are slightly longer. New, horizontal and inclined (10° and 20°) surfaces of 15-cm thick plaster plates (35  30 cm) were exposed to rain. The experiment lasted 2,100 h. The plates were completely dissolved in the rain. In addition to the characteristic formation of surfaces inclined at different angles, we were mainly interested in their long-term development and the changes that occurred throughout. The surfaces and the peaks dissected. Their changing forms influenced the further development of individual rock forms and the overall rock relief. Important results were acquired about the development model for this type of formation on barren rock peaks. We traced the slow sharpening of a plaster block by water flowing from the horizontal top and directly by rain. On the edges and walls, funnel-like notches and channels are either composite rock forms or one or the other factor prevails (Figs. 3.68 and 3.69). Once the walls are inclined, which of course first occurs in the upper section, they are distinctly shaped by rainwater. Larger channels are carved by creeping sheets of water, and rain flutes form where the creeping

86

M. Blatnik et al.

Fig. 3.68 Shaping of the wall of the plaster block

Fig. 3.69 Shaping of the wall of the plaster block

water does not reach them. The top is first dissected by smaller channels and then larger ones (Fig. 3.70). Between them rounded ridges first form that are later dissected by points or peaks dissected in turn by rain flutes (Figs. 3.70 and 3.71). The characteristic rock relief of a plaster plate inclined by 10° thus develops quite quickly with rain flutes that remain on the upper section of the block until the end, a flat middle section and channels on the bottom section (Slabe 2009). Larger parallel channels develop from a branched network of small channels (Fig. 3.72), and smooth surfaces dissect into steps (Knez et al. 2015). The channels become ever larger, true channel-like notches, shallow and dissected by smaller parallel channels (Fig. 3.73). Between

them there are distinct ribs and funnel-like notches become ever larger at the end. At the bottom of a channel-like notch, a single channel dominates that grows larger and larger until it develops into a new channel-like notch (Figs. 3.74 and 3.75). And then the development cycle is repeated again. The rapid solubility of plaster appears to affect the development. On limestone, rain flutes as well as short-term small channels also develop on ribs between channel-like notches. Rain flutes dissect the entire surface of the steep top wall of the block and the upper sections of the gradually sloping side walls that were originally vertical. Deep and slightly meandering channels develop on the bottom of the overhanging wall.

3

Lithomorphogenesis of Karst Surface

Fig. 3.70 Development of horizontal top of plaster block exposed to the rain

87

Fig. 3.72 Development of 10° inclined top of the plaster block exposed to the rain

Fig. 3.71 Development of horizontal top of plaster block exposed to the rain

Fig. 3.73 Development of 10° inclined top of the plaster block exposed to the rain

First, steps form beneath the sheet of flowing water over the top of the plaster plate inclined by 20°. Rain flutes then develop on the upper section, the middle becomes smooth, and below meandering and parallel channels develop (Figs. 3.76 and 3.77). Between some of the channels, ribs with rounded tops develop, and at their ends, funnel-like notches. The channels grow upwards and the ribs become ever sharper, shaped by rainwater. The latter develop into channel-like notches with small channels on their bottoms (Fig. 3.78). This form is similar to the one on the 10°-block

but more distinct. The channels at the bottom of the channel-like notches increasingly dominate. They grow larger to form new notches and new small channels form on their bottoms. The models clearly reveal the development of rock relief by the same factor (rain) as well as the developing transformation of rock forms. Rock relief is decisively influenced by the three-dimensional dissection of rock and the previous forms on it. We can single out two particular features that show us the development of characteristic rock forms. On

88

Fig. 3.74 Development of 10° inclined top of the plaster block exposed to the rain

Fig. 3.75 Development of 10° inclined top of the plaster block exposed to the rain

steep surfaces, rain flutes develop first in the upper section with small channels below them, and then rain flutes develop across the entire surface (Fig. 3.79). Funnel-like notches gradually form on the upper side of this surface with rain channels (rinnenkarren) below them that are dissected by rain flutes. On the second model, the bottom section of the top of the block is dissected after 125 h by a dense network of small channels, and on the third model, distinct individual channels already dominate. The inclination of the block influences the development of the rock forms, and the formation of parallel channels dominates.

M. Blatnik et al.

Fig. 3.76 Development of 20° inclined top of the plaster block exposed to the rain

Fig. 3.77 Development of 20° inclined top of the plaster block exposed to the rain

3.3.4 Rock Relief in the Plaster Tube The diameter of all the sections of the tube (Fig. 3.80) had increased on average by 1 cm. The experiment was terminated when the water widened the fissure in the middle section and began to leak through it substantially. In the wider inflow section of the tube, the scallops are 2 cm long (Figs. 3.80 and 3.81) and 4 cm in the outflow section. These are mature networks of scallops and the scallops are therefore evenly intertwined in the network. The first

3

Lithomorphogenesis of Karst Surface

89

Fig. 3.78 Development of 20° inclined top of the plaster block exposed to the rain

Fig. 3.79 Development of 20° inclined top of the plaster block exposed to the rain

network still displays a slight elongation of the scallops and openness on the outflow side (Slabe 1995a, b) but the second network practically neither. The second network is also affected by space since the water swirls evenly throughout the entire cross section, meaning that the swirling action dominates the characteristics of the rock (Slabe 1995a, b, 32). Three types of ceiling pockets can be identified. The first type forms on the circumference of the middle section of the model. They reach 1 cm in diameter and have a relatively regular semi-circular shape (Fig. 3.81a) while oblong features form only along the most distinct obstacles (non-homogeneous elements, cracks) in the plaster. Shallow

pockets have runoff tails in the direction of the water current. They are a transitional form between scallops and pockets. The second type of the pocket is linked to the areas of the most distinct swirling near abrupt changes in the diameter of the tube, specifically on the walls after the widening and before the narrowing of the tube. These pockets dominate at the junction of the wall of the widest part of the model and the cross-walls after the narrowing and before the widening of the tube. The largest and most unique pockets formed along the fissure that crossed the centre of the model (Figs. 3.80 and 3.81a). They are meandering and cylindrical in shape or resemble slightly narrowing cones with truncated

90

M. Blatnik et al.

Fig. 3.80 Plaster tube with rock relief

tops. The mouths of the largest pockets reach 3 cm in diameter. Along the most distinct part of the fissure they lie side by side, merging in a sponge-like perforation of the plaster with a dominant inside to outside direction. Depending on the width and depth of the fissure, such areas could be 10 cm long and 7 cm wide. Pockets and dissected cracks formed over the entire circumference of the tube, including on the floor of the passage as well as on the walls and the ceiling. The rock relief reflects the final hydraulic situation in the plaster tube. Of course, it is reasonable to conclude that at the beginning of the experiment the water current was faster in the outflow section of the tube and that the scallops on the circumference were smaller and the opposite applied in the inflow section. Detailed monitoring was not possible. Later when the crack along the fissure widened, the water current flowed faster through the inflow part of the tube and the crack, and the current flowed more slowly through the outflow pipe. The formation of deep pockets along the crack, however, is by far the most telling part of the experiment. Initially, the pockets were narrow and several centimetres deep but along the more distinct section of the fissure they grew into domes with pockets on both their tops and their circumferences. This development is characteristic of numerous karst caves. In the model, the pockets are found on the entire cross section of the circumference and are wider of course along

the more permeable sections of the fissure. The rock relief and the development of the tubes clearly indicate the importance of increased pressure and the widening of the passage along weak spots. Here we should especially emphasize the comparison with hypogenic caves and advise against hasty explanations that describe the majority of the emphasized forms from longitudinal cross sections of passages as traces of the hypogenic development of caves. The water current swirls over the entire cross section and thus pockets form. The descriptions of pockets in karst caves in most cases present ceiling pockets. They form on the ceilings because water currents typically transport solid material that carves the floor of the passage through erosion or covers it with sediment thus protecting it from corrosion. The origin of pockets whose formation is possibly also influenced by gases in the water and convection due to variations in their level of saturation in the solution is a subject for a future experiment.

3.3.5 Dissolution and Formation of Relief Along a Bedding Plane of Plaster and Siporex Layers The purpose of the experiment forcing water to percolate between layers of plaster and siporex of varying solubility was to simulate the percolation of water and the formation

3

Lithomorphogenesis of Karst Surface

Fig. 3.81 Rock features of plaster tube

91

92

M. Blatnik et al.

experiment, due to the faster and more turbulent flow and swirling along the harder fragments, the water completely transformed the longitudinal and parallel channels into a deep network of pockets, domes and scallops. Towards the end of the experiment, the scallops started to grow, indicating a gradual slowing of the water flow through the model. With the slow water flow, the small interbed anastomoses grew into a larger channel with wall forms characteristic of a slow water flow.

3.4

Fig. 3.82 Plates of different composition

of relief in natural conditions along bedding planes of homogeneous rock with uniform granulation, along bedding planes of clastic rock containing clasts that dissolve more slowly than the surrounding material, and along bedding planes of rock with a low percentage of soluble carbonate. We put together a model of siporex (autoclaved aerated concrete) plates used in construction, pure plaster and layers composed of two different materials: broken fragments of plaster (with average volumes of a few cm3) containing Portland cement added during the mixing for greater hardness (slower solubility) were covered with pure plaster (Figs. 3.82 and 3.83). The stack of plaster and siporex layers was placed in a flume with a rectangular 1.4  3.4 m cross section. The average level of the water in the flume was 95 cm with an average discharge of 360 L/s of the water, temperature was 12.4 °C. The experiment revealed the dissolving and formation of relief on the surface of layers of varying solubility and composition. At the beginning of the experiment, the water dissolved only the faces and outer contacts between the layers. The next stage, with a predominantly laminar and slower flow between layers, saw the formation of longitudinal and meandering anastomosis channels, in some places the origins of a network of scallops, and along the harder, more slowly dissolving fragments, the beginnings of pockets and domes created by swirling water. In the last phase of the

Development Model of Rock Relief Formation on Thick Horizontal and Gently Sloping Beds of Rock Exposed to Rain

We are finishing the research on the development model of rock relief formation on thick horizontal and gently sloping beds of rock exposed to rain and here we are presenting its preliminary results. Rain falls on a thick (more than one metre) barren bed of carbonate rock, an extensive flat top of karren. The strata are horizontal or slightly inclined, in our model from 0° to 20°. In the development of karren and stone forests, such conditions often occur due to the more rapid decomposition of thin or distinctly fissured upper beds of rock (e.g. Vransko jezero in Dalmatia, Croatia, or a stone forest in Peruaçu, Brazil). The surfaces of the top of the beds are relatively smooth if the beds lie closely one on top of another, if cavities do not form between them, if they are not fissured, and if water does not flow to the contact.

3.4.1 Development Model Rock relief is an existing, momentary state in the most often rich and varied formative homogeneous or heterogeneous (e.g. denuded rock) development of karst phenomena. A different form of rock relief thus reflects different ways and conditions for the formation of a karst phenomenon and different developmental stages under the same conditions and the same factors. For this reason, a knowledge of different formations of rock surface (barren, covered, overgrown, etc.) and of development models of homogeneous rock formation over time is essential. The development model (Figs. 3.84 and 3.85) of the formation of horizontal and gently sloping thick beds of rock exposed to rain is part of the latter knowledge. On initially smooth horizontal surfaces, water first forms rock peaks

3

Lithomorphogenesis of Karst Surface

Fig. 3.83 Development of bedding-plane features

93

94

M. Blatnik et al.

Fig. 3.84 Developing model of slightly inclined surface of the rock

which then develop into tops of karren with funnel-like notches and channels between them. On inclined surfaces, a more distinct sheet flow occurs that forms the dominant steps (Figs. 3.84a and 3.85a). Rain flutes only develop on the upper side wall and the higher sections of the eventually dissected surface. Solution pans form as well. Over time, sheet flow begins to consolidate into streams (Figs. 3.84c and 3.85b), more rapidly on surfaces with steeper inclinations, and channels develop that as a rule grow from the bottom up from the funnel-like notches at the lower edge of the top surface. On the most gently sloping surfaces, a network of channels first develops while single and parallel channels develop on more distinctly inclined surfaces. Three-dimensional dissection is increasingly distinct.

Solution pans open and their walls and the walls of larger steps, the steeper parts, are dissected by rain flutes (Fig. 3.84c). Wider peaks are dissected by a network of ever deeper channels (Fig. 3.85d) and funnel-like notches (Figs. 3.84d and 3.85e), and therefore steep surfaces and pointed or meandering blade-like tops dominate (see Sect. 3.2). The development of this type of formation of peaks is presented in a generalized fashion since within the described and already so varied development, numerous states and their variations have been revealed. Rock forms change gradually through numerous formative transitions and merge into one another (e.g. solution pans, steps, funnel-like notches). A challenge for the future.

3

Lithomorphogenesis of Karst Surface

Fig. 3.85 Developing model of the inclined (10° and more) surface of the rock

95

96

References Allen JRL (1972) The origin of cave flutes and scallops by enlargement of inhomogeneities. Rass Speleol Ital 14(1):3–20 Berbert-Born M (2000) Carste de Lagoa Santa. In: Schobbenhaus C, Campos DA, Queiroz ET, Winge M, Berbert-Born M (eds) Sítios Geológicos e Paleontológicos do Brasil. http://www.unb.br/ig/ sigep/sitio015/sitio015.htm Chen Z, Song L, Sweeting MM (1983) The Pinnacle Karst of the Stone Forest, Lunan, Yunnan, China: an example of sub-jacent karst. New direction in karst. In: Proceedings of the Anglo-French Karst symposium. Norwich, England, pp 597−607 Curl RL (1966) Scallops and flutes. Trans Cave Res Group GB 7 (2):121–160 Day M, Waltham T (2009) The pinnacle karrenfields of Mulu. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 423−432 Dzulynski S, Gil E, Rudnicki J (1988) Experiments on kluftkarren and related lapis forms. Z Geomorphol NF 32:1–16 Engelhardt W, Füchtbauer H, Müller G (1964) Sediment-Petrologie, Methoden der Sediment-Untersuchung, Teil 1. E. Schweizerbartische Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, p 303 Ewers RO (1966) Bedding plane anastomoses and their relation to cavern passages. Bull Speleol Soc 28(3):133–141 Ewers RO (1972) A model for the development of subsurface drainage routes along bedding planes. MSc thesis. University of Cincinnati, p 84 Ewers RO (1982) Cavern Development in the Dimensions of Length and Breadth. PhD thesis. McMaster University, Hamilton, p 398 Ford D, Williams P (1989) Karst geomorphology and hydrology. Unwin Hyman, London, p 601 Ford DC, Williams PW (2007) Karst hydrogeology and geomorphology. Wiley, Chichester, p 562 Ford D, Salomon JN, Williams P (1996) Les “Forêts de Pierre” ou “Stone forests” de Lunan. Karstologia 28(2):25–40 Ford D, Salomon JN, Williams P (1997) The Lunan Stone forest as a potential world heritage site. Stone forest a treasure of natural heritage, Proceedings of International Symposium for Lunan Shilin to Apply for World Natural Heritage Status. Bejing, China, pp 107−123 Gabrovšek F, Knez M, Kogovšek J, Liu H, Petrič M, Mihevc A, Otoničar B, Slabe T, Šebela S, Zhang S, Zupan Hajna N (eds) (1998) South China Karst I. ZRC Publishing, Ljubljana, p 247 Ginés A, Knez M, Slabe T, Dreybrodt W (eds) (2009) Karst rock features, karren sculpturing, Carsologica 9. ZRC Publishing, Ljubljana, p 561 Glew JR (1976) The simulation of rillenkarren. Unpublished MSc thesis, McMaster University, Hamilton, Ontario, p 116 Glew JR, Ford DC (1980) A simulation study of the development of rillenkarren. Earth Surf Process 5:25–36 Gomez-Pujol L, Fornos JJ (2009) Microrills. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 73–85 Goodchild JG, Ford DC (1971) Analysis of scallop patterns by simulation under controlled condition. J Geol 79(1):52–62 Goudie A (2009) Cavernous weathering. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 89–103 Grimes KG (2009) Solution pipes and pinnacles in syngenetic karst. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 513−523 Gutiérrez Domech R, Knez M, Slabe T (2015) Felo Pérez Mogote (Viñales, Pinar del Río, Cuba): typical shaping of rock surface below dense tropical vegetation. Acta Carsolog 44(1):47–57

M. Blatnik et al. Habič P (1980) S poti po kitajskem krasu (summary: From the way to the Chinese karst). Geogr Vest 52:107–122 Hantoon PW (1997) Definition and characteristics of Stone forest epikarst aquifers in south China. In: Proceedings of 12th international congress of speleology, vol 1, Symposium 8. La Chaux-de-Fonds, Switzerland, pp 311−314 Hunt CO (1996) Tafoni (pseudokarst features) in the Maltese Islands. Cave Karst Sci 23(2):57–62 IBGE (1993) Mapa de vegetação do Brasil, 1:1500.000 Jennings JN (1973) Karst. The M.I.T. Press, Cambridge, Massachusetts, and London, England, p 253 Klimchouk AB (2000) Dissolution and conversion of gypsum and anhydrite. In: Klimchouk AB, Ford DC, Palmer AN, Dreybrodt W (eds) Speleogenesis. Evolution of karst aquifers, Huntsville, Alabama, pp 160–168 Knez M (1996) Vpliv lezik na razvoj kraških jam. Primer Velike doline, Škocjanske jame (summary: The bedding-plane impact on development of karst caves. An example of Velika dolina, Škocjanske jame caves). Zbirka ZRC 14, Ljubljana, p 186 Knez M (1997) Prvi rezultati raziskav kamnine v treh lunanskih kamnitih gozdovih (Yunnan, Kitajska). Summary: First results of rock research in three Lunan stone forests (Yunnan, China). Acta Carsolog 26(2):431−439 Knez M (1998a) The influence of bedding-planes on the development of Karst caves (a study of Velika Dolina at Škocjanske Jame caves, Slovenia). Carbonates Evaporites 13:121–131 Knez M (1998b) Lithologic properties of the three Lunan stone forests (Shilin, Naigu and Lao Hei Gin). In: Chen X et al (eds) South China Karst I. ZRC Publishing, Ljubljana, pp 30–43 Knez M, Slabe T (2001a) Shape and rock relief of the pillars in Naigu stone forest, SW China. Acta Carsolog 30(1):13–24 Knez M, Slabe T (2001b) The lithology, shape and rock relief of the pillars in the Pu Chao Chun stone forest (Lunan stone forests, NW China). Acta Carsolog 30(2):129–139 Knez M, Slabe T (2002) Lithologic and morphological properties and rock relief of the Lunan stone forests. In: Gabrovšek F (ed) Evolution of karst: from prekarst to cessation. Carsologica 1, ZRC Publishing, Ljubljana, pp 259−266 Knez M, Slabe T (2006a) Lithological and morphological characteristics and rock relief of the Lao Hei Gin shilin-stone forest (Lunan, SW China). Acta Carsolog 35(1):99–105 Knez M, Slabe T (2006b) Litološke in reliefne značilnosti lunanskih kamnitih gozdov na južnokitajskem krasu. Geogr Vestn 78 (1):9–24 Knez M, Slabe T (2007) Shilin: the formation of stone forests in various rock types (Lunan, Yunnan, China). Acta Geol Sin (Engl. ed.) 81 (1):148−157 Knez M, Slabe T (2009) Lithological characteristics, shape and rock relief of the Lunan stone forest. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, pp 439−452 Knez M, Slabe T (2010) Karren of Mushroom Mountain (Junzi Shan) in the eastern Yunnan ridge, Yunnan, China, karstological and tourist attraction. Acta Geol Sin (Engl. ed) 84(2):424–431 Knez M, Slabe T (2011) South China Karst II. Carsologica 12, ZRC Publishing, Ljubljana–Postojna, pp 9−60 Knez M, Slabe T (2013) Stone forests and their rock relief. In: Shroder JF (ed) Treatise on geomorphology, vol 6, 1st edn. Academic Press: Elsevier, San Diego, pp 139−156 Knez M, Kogovšek J, Slabe T (1997a) Karst researches in Yunnan Province, China. Acta Carsolog 26(2):491–496 Knez M, Kogovšek J, Slabe T (1997b) Kamniti gozd: raziskovanje krasa v kitajski provinci Yunnan. Kras: revija o Krasu in krasu, o ljudeh in njihovem ustvarjanju 24:40−43

3

Lithomorphogenesis of Karst Surface

Knez M, Slabe T, Šebela S (2004) Karst uncovered during the BičKorenitka motorway construction (Dolenjska, Slovenia). Acta Carsolog 33(2):75–89 Knez M, Liu H, Slabe T (2010) High mountain karren in northwestern Yunnan, China. Acta Carsolog 39(1):103–114 Knez M, Liu H, Slabe T (eds) (2011a) South China karst II. Carsologica 12, ZRC Publishing, Ljubljana, p 237 Knez M, Slabe T, Panisset T, Luiz E (2011b) Karren on laminar calcarenitic rock of Lagoa Santa (Minas Gerais, Brazil). Acta Carsolog 40(2):357–367 Knez M, Liu H, Slabe T (2012) Major stone forest, litomorphogenesis and development of typical shilin (Yunnan, China). Acta Carsolog 41(2−3):205−218 Knez M, Rubinić J, Slabe T, Šegina E (2015) Karren of the Kamenjak hum (Dalmatian Karst, Croatia): from the initial dissection of flat surfaces by rain to rocky points. Acta Carsolog 44(2):191–204 Knez M, Liu H, Slabe T (2017) Shui Jing Po Shilin, rock and relief of stone forests on Cone Hills, Yunnan, China. In: Renard P, Bertrand C (eds) EuroKarst 2016, Neuchâtel advances in the hydrogeology of karst and carbonate reservoirs. Advances in karst science. Springer, Cham, pp 3–19 Kogovšek J, Liu H (1999) Water tracing test in the Tianshengan region, China, at low water level in November 1998. Acta Carsolog 28 (2):241–253 Kogovšek J, Liu H (2000) Water tracing test in the Tianshengan region, Yunnan-China, at high water level. Acta Carsolog 29(2):249–260 Kogovšek J, Kranjc A, Slabe T, Šebela S (1999) South China Karst 1999, preliminary research in Yunnan. Acta Carsolog 28(2):225 −240 Kohler HC (1989) Geomorfologia cárstica na região de Lagoa Santa. PhD thesis, USP, São Paulo, p 113 Kranjc A, Liu H (2001) Lunan Shilin (stone forest) human impact and protection of (eventual) world heritage site (Yunnan, China). Acta Carsolog 30(1):25–38 Kunaver J (2009) Corrosion terraces, a megaausgleichfläche or a specific landform of bare glaciokarst. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 161−168 Lauritzen SE (1981) Simulation of rock pendants—small scale experiments on plaster models. In: Beck BF (ed) Eight international congress of speleology. Georgia Southwestern College, Americus, Georgia, pp 407–409 Magaš D (1990) Osnovna geografska obilježja Biogradske mikroregije. Biograd i njegova okolica u prošlosti. In: Zbornik radova (Š. Batović, ed.), Zavod za povijesne znanosti Filozofskog fakulteta, Zadar, SIZ kulture općine Biograd, Biograd, pp 39−84 Maire R, Zhang S, Song S (1991) Genèse des karsts subtropicaux de Chine du Sud (Guizhou, Sichuan, Hubei). Karstol Mém 4:162–186 Mangin A (1997) Some features of the stone forest of Lunan, Yunnan, China. Stone forest a treasure of natural heritage. In: Proceedings of international symposium for Lunan Shilin to apply for world natural heritage status. Bejing, China, pp 68−70 Narbona JG (1989) Sima Rasca (El Torcal, Antequera, Malaga). Andal Subterr 9:51–64 Ohde S, Kitano Y (1982) Distribution of protodolomite in Minami-daito-jima, Okinawa. Bull Coll Sci Univ Ryukyus 33:81– 87 Ollier C (1984) Weathering. Longman, London and New York, p 270 Ota T, Utsunomiya A, Uchio Y et al (2007) Geology of the Gorny Altai subduction–accretion complex, southern Siberia: Tectonic evolution of an Ediacaran-Cambrian intra-oceanic arc-trench system. J Asian Earth Sci 30:666–695 Patrus MLRA (1996) Hidrologia e kualidade de áquas de superfície do municipío de Sete Laguas. Belo Horizonte, CPRM (Projeto VIDA– Programa gestão e Administrção Territorial)

97 Perna G, Sauro U (1978) Atlante delle microforme di dissoluzione carsica superficiale del Trentino e del Veneto. Memoire del Museo Tridentino di Scienze naturali 22:189–199 Perne M, Gabrovšek F (2009) The problems of rillenkarren development: a modeling perspective. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 55−61 Pleničar M, Premru U (1977) Tolmač za list Novo Mesto. Osnovna geološka karta SFRJ (Explanations to the map of Novo Mesto). Basic geological map of SFRJ 1:100,000, Beograd, p 61 Pluhar A, Ford DC (1970) Dolomite karren of the Niagara escarpment, Ontario, Canada. Z Geomorph 14(4):392–410 Quinif Y (1973) Contribution à l’étude morphologique des coupoles. Annal Spéléol 28(4):565–573 Rodriguez-Navarro C, Doehne E, Sebastian E (1999) Origins of honeycomb weathering: the role of salts and wind. Geol Soc Am Bull 111(8):1250–1255 Rudnicki J (1960) Experimental work on flutes development. Speleologia 2(1):17–30 Salomon J-N (1997) Comparaison entre les “Stone forests” du Lunan (Yunnan-Chine) et les Karsts à “Tsingy” de Madagascar. In: Song L, Waltham T, Cao N, Wang F (eds) Stone Forest, a treasure of natural Heritage, Beijing, pp 124−136 Salomon J-N (2009) The tsingy karrenfields of Madagascar. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 411−422 Slabe T (1994) Dejavniki oblikovanja jamske skalne površine (The factors influencing on the formation of the cave rocky surface). Acta Carsolog 23(2):369–398 Slabe T (1995a) Cave rocky relief and its speleogenetical significance. ZRC 10, Ljubljana, p 128 Slabe T (1995b) Experimental modelling of cave rocky relief forms in Paris plaster. Atti e Memorie della Commissione Grotte E. Boegan 32:65–83 Slabe T (1998) Rock relief of pillars in the Lunan Stone Forest. In: Gabrovšek et al (eds) South China karst 1. ZRC Publishing, Ljubljana, pp 51−67 Slabe T (2005) Two experimental modelings of karst rock relief in plaster: subcutaneous «rock teeth» and «rock peaks» exposed to rain. Z Geomorph NF 49:107–119 Slabe T (2009) Karren simulation with plaster models. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 47–54 Slabe T, Liu H (2009) Significant subsoil rock forms. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 123−137 Slabe T, Hada A, Knez M (2016) Laboratory modeling of karst phenomena and their rock relief on plaster, subsoil karren, rain flutes karren and caves. Acta Carsolog 45(2):187–204 Song L (1986) Origination of stone forest in China. Int J Speleol 15:3–33 Song L, Li Y (1997) Definition of Stone forest and its evolution in Lunan County, Yunnan, China. In: Stone forest a treasure of natural heritage, Proceedings of international symposium for Lunan Shilin to apply for world natural heritage status. Bejing, China, pp 37−45 Song L, Liang F (2009) Two important evolution models of Lunan Shilin karst, Yunnan, China. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 453−459 Song L, Liu H (1992) Control of geological structures over development of cockpit karst in south Yunnan, China. Tübingen Geographische Studien 109:57−70 Song L, Wang F (1997) Lunan Shilin landscape in China. In: Proceedings of 12th international congress of speleology, vol. 1, Symposium 8. La Chaux-de-Fonds, Switzerland, pp 433−435

98 Suzuki Y, Iryui Y, Inagaki S, Yamada T, Aizawa S, Budd DA (2006) Origin of atoll dolomites distinguished by geochemistry and crystal chemistry: Kita-daito-jima, northern Philippine Sea. Sed Geol 183:181–202 Sweeting MM (1972) Karst landforms. Macmillan, London, p 362 Sweeting MM (1995) Karst in China. Its geomorphology and environment. Springer, Berlin, Heidelberg, New York, p 265 Šebela S, Slabe T, Kogovšek J, Liu H, Pruner P (2001) Baiyun Cave in Naigu Shilin, Yunnan Karst, China. Acta Geol Sin (Engl. ed.) 75 (3):279−287 Šebela S, Slabe T, Liu H, Pruner P (2004) Speleogenesis of selected caves beneath the Lunan Shilin and caves of Fenglin karst in Qiubei, Yunnan. Acta Geol Sin (Engl. ed.) 78(6):1289−1298 Tóth G (2007) A mérsékeltövi mészkő magashegységek fedetlen karros celláinak osztályozása és fejlődése. Classification and development of bare karren cells in calcareous high mountains. Classification et développement des cellule lapiasées nues alpines. BDF Természetföldrajzi Tanszék, Szombathely, p 116 Tóth G (2009) Karren features in Dachstein mountain (Austria). In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 313–322 Travassos EPL, Kohler HC (2009) Historical and geomorphological characterization of a Brazilian karst region. Acta Carsolog 38(2– 3):277–291 Trudgill ST (1985) Limestone Geomorphology. Longman, London and New York, p 196 Tućan F (1911) Die Oberflächenformen bei Carbonatgesteinen in Karstgegenden. Centr F Min Geol Paleont 1911:343–350

M. Blatnik et al. Urushibara-Yoshino K, Miotke F-D (1999) Solution rate of limestone in Japan. Phys Chem Earth (A) 24(10):899–903 Urushibara-Yoshino K, Lauritzen SE, Slabe T, Knez M, Oppata Y (2017) Karstification processes of Minamidaito Island, in Japan’s Nansei Islands. Chikei 38(2):107–128 Waltham AC (1984) Some features of karst geomorphology in south China. Cave Sci Trans Br Cave Res Assoc 11:185–199 Williams WP (1966) Limestone pavements with special reference to Western Ireland. Inst Br Geogr Trans 40:155–172 Williams PW (2009) Arête and pinnacle karst of mount Kaijende. In: Ginés A, Knez M, Slabe T, Dreybrodt W (eds) Karst rock features, karren sculpturing. Carsologica 9, ZRC Publishing, Ljubljana, pp 433−437 Yu Y, Yang B (1997) Paleoenvironment during formation of Lunan stone forest. In: Stone forest a treasure of natural heritage, Proceedings of international symposium for Lunan Shilin to apply for world natural heritage status. Bejing, China, pp 63−67 Yuan D (1991) Karst of China. Geological Publishing House, Beijing, p 224 Yuan D (1997) A global perspective of Lunan Stone forest. In: Stone forest a treasure of natural heritage, Proceedings of international symposium for Lunan Shilin to apply for world natural heritage status. Bejing, China, pp 68−70 Zhang F, Wang F, Wang H (1997) Lunan Stone forest landscape and its protection and conservation. In: Stone forest a treasure of natural heritage, Proceedings of international symposium for Lunan Shilin to apply for world natural heritage status. Bejing, China, pp 71−77 Zhang F, Geng H, Li Y, Liang Y, Yang Y, Ren J, Wang F, Tao H, Li Z (1997b) Study on the Lunan stone forest karst. Yunnan Science and Technology Press, Kunming, China, p 155

4

Significant Findings from Karst Sediments Research Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

About 44% of Slovenia’s surface consists of carbonate rocks. Karst geomorphology and over 13,000 known caves represent a significant proportion of its landscape. Various sediments present on the karst surface in the form of clastic or precipitated deposits can cover or fill smaller or extended areas and they can also accumulate in the caves. In the last decades, study and interpretations of the karst sediments in Slovenia went through different stages in accordance with various theoretical models and were recently upgraded, especially by development of dating methods and by improved knowledge about karst processes. Karst surface sediments are mechanical or chemical deposits (Fig. 4.1). Mechanical sediments on the karst surface represent all kinds of clastic material deposited by surface processes such as: fluvial (e.g. gravel, sand, silt, clay); conglomerate forming for instance alluvial fans, terraces; lacustrine; glacial, fluvioglacial and periglacial material (e.g., till forming moraines, diamicton and diamictite); and slope material (e.g. talus cones, rockfalls). Chemical deposits related to environment and climate factors (e.g. tufa, travertine), different carbonate crusts (e.g. calcrete, caliche) and calcite cements in bulk material are also represented. Various soils may be formed due to development from insoluble residues (e.g. in situ pedogenesis) or clastic allochthonous sediments (e.g. fluvial, eolian). Former cave M. Blatnik
F. Gabrovšek
M. Knez (&)
B. Kogovšek
J. Kogovšek
C. Mayaud
A. Mihevc
J. Mulec
M. Năpăruş-Aljančič
B. Otoničar
M. Petrič
T. Pipan
M. Prelovšek
N. Ravbar
T. Shaw
T. Slabe
S. Šebela
N. Zupan Hajna Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia e-mail: [email protected] D. C. Culver American University, Washington, DC, USA H. Liu Yunnan University, Kunming, China

sediments from unroofed caves, such as clastic sediments and speleothems can also be found on the surface. Cave sediments represent all types of mechanical and chemical depositions in the caves (Fig. 4.2). According to their origin, they are divided into allochthonous and autochthonous sediments (Ford and Williams 2007). Allochthonous deposits were brought into caves from outside and represent all kinds of clastic sediments, such as gravel, sand, silt, clay (when cemented: conglomerate, sandstone, siltstone, claystone) or organic matter such as plant debris, coarse woody debris and bones. The most common allochthonous cave deposits are allogenic sediments which are brought into caves by sinking rivers. Most common are gravel, sand, silt and clay size materials originating from weathered bedrocks and sediments of the sinking river catchment area. Infiltration sediments which are brought into a cave through open fissures or cave entrances and are composed of various surface clastic sediments and soils (e.g. “terra rossa”) are also allochthonous, as are eolian and glacial or periglacial materials which can be present at the entrance areas of the caves (e.g. loess, till, lacustrine sediments). Autochthonous clastic sediments are all deposits formed in caves. These include breakdown and crumbled wall materials as well as chemical deposits like secondary cave minerals and speleothems. Chemical deposits precipitate from a supersaturated solution in the form of various speleothems; they differ in shape, mineral composition, colour and age. The shape is determined by the mode of water inflow which can include dripping, flowing, seeping, pooled and capillary water. Speleothem mineral composition and colour depend on the composition of bedrock and vegetation above the cave. The most common minerals that form speleothems in limestone caves are calcite (CaCO3), aragonite (CaCO3) and gypsum (CaSO4  2H2O). Speleothem colour depends on the mineral composition, metal impurities, soil and surface vegetation cover. Speleothems are of different ages, ranging from

© Springer Nature Switzerland AG 2020 M. Knez et al. (eds.), Karstology in the Classical Karst, Advances in Karst Science, https://doi.org/10.1007/978-3-030-26827-5_4

99

100

M. Blatnik et al.

Fig. 4.1 Various sediments on karst surface: a lacustrine sediments in the dry bottom of Cerknica polje; b tufa barriers on Krka river; c red soil above subsoil karren in Dolenjska region may be infiltrated deep

into the karst underground; d stalagmite surrounded by cave allogenic sediments in an unroofed cave above Škocjanske jame

the youngest which are still growing to those millions of years old. Karst sediments, both on the surface and in caves, represent an important source of information on the evolution of tectonic and geomorphological units of different sizes. Fluvial sediments, for instance, indicate the abundance of precipitation and hydrological characteristics. The shapes of speleothems made of secondary calcite specify the way of water percolation. The mineral composition, various inclusions and stable isotope geochemistry indicate physio-chemical conditions at the time of their precipitation. The dynamics of sedimentation is mainly controlled by climate and hydrology (e.g. glaciations, floods, precipitation), by changes in river catchment and by the evolution of cave networks. Protected in caves, sediments are generally well preserved and reveal exceptionally good, multi-proxy records of surface environmental conditions at the time of their deposition; they can cover time spans from several million years up to the present (Bosák 2002). Cave sediments represent traps of past geologic and environmental records in spite of the fact that they mostly represent the latest episodes of

deposition. Many times sediments from diverse karst environments are the only sediments representing terrestrial phases of landscape evolution and they indirectly indicate the age of speleogenesis and surface evolution. The question concerning the time span of karst evolution in Slovenia, the age of karst surfaces and speleogenesis and, consequently, the rates of processes, have been an important issue in most of the previous karst studies and syntheses. The majority of dating of karst sediments has been recently carried out in SW Slovenia (i.e. in the NW part of the Dinaric Karst) which is known as the Kras. Eocene flysch rocks are the last marine deposits preserved in the geologic record. Oligocene to Quaternary rocks represents a terrestrial period where surface denudation and erosion processes prevailed. Karst sediments preserved on the surface are therefore rare; but caves have functioned as traps of clastic, chemical and organic sediments derived from local as well as more distant environments during the life of a cave. The position and composition of cave fill, including fossil remains, tends to be preserved for great time spans and can offer useful information on the evolution of surface geology, morphology and also a cave itself.

4

Significant Findings from Karst Sediments Research

101

Fig. 4.2 Characteristic cave sediments: a various speleothems in Tartarus (Postojnska jama); b aragonite crystals from Bevkova jama; c river sediments (pebbles) from Škocjanske jame; d bones and teeth of Ursus spelaeus from Križna jama

4.1

Karst Sediments Research in Slovenia

The territory of Slovenia, with its numerous karst regions from the Alps to the Mediterranean, long history of karst evolution and relatively good knowledge of karst sediments, represents an ideal place for studies and dating of cave sediments with different research methods. The results obtained have been used for interpretation of sediment origins, deposition time as for time of caves and karst evolution of selected Slovenian regions. The first estimates of the age of the karst in Slovenia were made by geologists and karst geomorphologists. They utilized geologic data such as the age of the last marine sedimentation and the tectonic evolution of the Dinaric Mountains and the Alps (e.g. Grund 1914), sediments on the karst surface and some distinct forms of the relief. Roglić (1957), Melik (1961) and Radinja (1972, 1986) defined a pre-karst phase when rivers were flowing across the karst surface and deposited fluvial sediments, and the karstification phase when rivers began to sink at the edges of the karst.

The early systematic studies of cave sediments were carried out during archaeological excavations of sediments in the entrance parts of some caves (Brodar 1952, 1966). Gospodarič (1972, 1976, 1981, 1988) started with more extensive and detailed studies of cave sediments; but he suspected that the cave sediments were not much older than 350 Ka. It was suspected that the karst started to evolve during Pliocene times (e.g. Brodar 1966; Gospodarič 1988; Habič 1992). A better understanding of cave sediments and their age and the chronological sequence of speleological events was achieved by more concentrated dating by the Th/U method (Zupan 1991; Zupan Hajna 1996; Mihevc and Lauritzen 1997; Mihevc 2001a). The application and interpretation of paleomagnetic analysis and magnetostratigraphy of the cave sediments, both clastic and chemogenic, began in 1997, suggested substantial changes in the lower limiting ages of cave fill deposition (Bosák et al. 1998, 1999, 2000a, b, 2004; Šebela and Sasowsky 1999, 2000; Audra 2000; Mihevc et al. 2002; Zupan Hajna et al. 2008a, b, 2010; Knez et al. 2016). The study of cave deposits in Alpine caves and in unroofed caves of the Kras provided entirely new insights

102

into the age of cave and karst sediments and introduced new ideas concerning the development of karst. Presented here are some examples of recent findings during karst sediment research and their interpretations which sometimes have come into conflict with existing karst concepts.

4.1.1 Surface Clastic Sediments and Red Soil One of the characteristics of the Slovenian karst is red soil— terra rossa-type, although the colour of clastic sediments includes all varieties from yellow to red. In general, not a lot of soil is on the karst surface with the exception of accumulations in dolines or depressions. On the other hand, there are thick sediment/soil covers present in some areas of Southern Slovenia which is the most northern part of the Dinaric Karst. Terra rossa-type red soils are composed of reddish clayey to silty material covering karst landscapes in hot/warm climates (Fedoroff and Courty 2014), such as those in the Mediterranean part of Dinaric Karst. The origin of red soil in Slovenia was at first attributed to insoluble remains of limestone, especially those containing cherts (Gregorič 1967; Culiberg et al. 1997; Rejšek et al. 2012). In the Kras Plateau in SW Slovenia, red soil is called “jerovica” (Fig. 4.3a); jerovica is a characteristic soil developed on Cretaceous limestone with chert, such as the Komen limestone of the Sežana Formation and the Tomaj limestone of the Lipica Formation (Jurkovšek et al. 1996). Different opinions were related to the nature of its parent material and origin. Red soil in Slovenia was studied from different aspects, including its composition and origin by Hrovat (1953), Gregorič (1967, 1969) and its accumulation in dolines by Gams (1974, 2004). Later, a possible eolian origin as loess sedimentation during Pleistocene was considered (Šušteršič et al. 2009). Red soils origin and their

M. Blatnik et al.

relationship to underlying carbonates and existing karst relief have been, and still are, the subject of discussion. Recent research on red soils from different parts of Slovenian karst found that they originate in weathered remains of limestones rich in chert, in weathered remains of flysch rocks, in local weathered noncarbonate rocks (Zupan Hajna et al. 2019), or even from the alluvium of unroofed caves and they are almost negligible in eolian sediments (Zupan Hajna 2000, 2005; Zupan Hajna et al. 2017). Red soils on the karst surface may differ in respect of mineral composition and thus also by their origin and time of development (Zupan Hajna 2000, 2005; Zupan Hajna et al. 2017). For instance, most of the red clays and soils around Divača village (south part of Kras Plateau) have their origin in weathered flysch rocks (Zupan Hajna 1992, 1998a, b, 2000, 2002; Fig. 4.5). Minerals such as microcline and plagioclase found in those red soils prove that they cannot be insoluble remains of limestone. In sediments from caves close to the surface and from unroofed caves sediments, no minerals indicating loess origin were found (e.g. amphiboles which are typical of loess sediments in Istria; Durn 2003), thus eolian origins can be excluded; even some of them from unroofed caves there were dated to 5–4 Ma (Zupan Hajna et al. 2008a, 2010). Some of the red coloured sediments and red soil passed through weathering in a period of tropical climate what is indicated by presence of bauxite minerals; examples are red clasts from cave sediments in Trhlovca Cave (Fig. 4.5). Some red clays on the surface (e.g. on the Kras Plateau, Dolenjska region) in the dolines and in the caves are not soils; they are actually clastic sediments which have had contact with percolating water from the surface and changed their colour during diagenesis in the oxidation zone from yellow to red due to the oxidation of goethite to hematite in clay pigment coatings (rubification) (Mihevc and Zupan Hajna 1996; Zupan Hajna 1998a, 2000; Knez et al. 2016; Zupan Hajna et al. 2017, 2019; Fig. 4.5). The study of the

Fig. 4.3 a Red soil composed of unsoluble remains of limestones with chert, Komen (Kras); b unroofed cave with quartz pebbles and sand on Slavenski ravnik

4

Significant Findings from Karst Sediments Research

mineralogical composition of yellow and red sediments from dolines around Divača village also showed that yellow colour is usually an indicator of sediments of Eocene flysch origin which were weathered in different degrees and after deposition in caves or karst depressions were protected against atmospheric influences (e.g. oxidation). If those yellow sediments were in contact with percolating meteoric water, they may have changed colour to red. The same process may occur in the caves. Occurrences of quartz pebbles and sands (Fig. 4.3b) on the karst surface were at first all attributed to fluvial transport of weathered remains of flysch rocks over karst in the so-called “pre-karst” phase (Melik 1961; Radinja 1972; Habič 1992). With further research and the discovery and geomorphological explanation of denuded caves, many of those sediments have since been determined to be surface exposures of cave sediments (Mihevc 1996; Mihevc and Zupan Hajna 1996; Zupan Hajna 1998a; Mihevc 2001a, 2007; Knez et al. 2016).

4.1.2 Cave Clastic Sediments Clastic sediments in caves differ in size, shape, colour, texture, mineral composition and therefore they have various proveniences. Mechanical cave sediments are categorized in terms of their autochthonous or allochthonous origins. Autochthonous mechanical cave sediments are due to weathering processes on cave ceilings and walls, allochthonous sediments are clay, silt, sand, and gravel originating from outside of the caves. In these sediments, various minerals are accumulated. From original rock to mechanical sediment in the cave, the minerals may be lost or changed. The changes of mineral composition occur either due to chemical weathering of the original rock, or during the transport or at later diagenesis of mechanical sediments in the cave. How many minerals and which of them are lost during the transport, is especially dependent on duration of transport. With respect to chemical and mechanical weathering, only the most resistant minerals remain as heavy minerals and quartz. The most important factors for the determination of the origin of cave mechanical sediments are the invariable mineral association and also the presence of some typical residual minerals. Less resistant minerals are replaced by clay minerals, chlorites, iron hydroxides, etc.

4.1.2.1 Cave Sediment Facies From a sedimentological point of view, the cave environment can be divided into an entrance facies and an interior facies. The farther away cave sediments are from cave entrances, the less they are subjected to environmental changes on the surface after deposition. During several years of research, we found that sediments in a cave could remain

103

completely unchanged for millions of years. In the vicinity of cave entrances, deposited sediments are influenced mainly by diurnal and seasonal changes in temperature and water intake (precipitation, floods), which can greatly alter the chemical and mechanical properties of existing sediments. The entrance facies includes fine-grained sediments transported from the vicinity of the cave by wind and water, coarser clasts transported into the cave by slope processes, or autochthonous sediments produced by frost action or other mechanical and chemical processes on the cave walls. The cave entrance contains pollen as well as datable archaeological and paleontological remains that are protected from surface erosion, weathering and biochemical alteration (Ford and Williams 2007). Entrance zones of caves are often exposed to seasonal freezing that causes spalling of cave walls and formation of fragments of various sizes which accumulate on the cave floor. Resulting sediments are often subject to creeping due to cryoclastic processes. Cryoturbated cave sediments in Slovenia were usually attributed to Pleistocene climates (e.g. Brodar and Brodar 1983; Turk et al. 2001), but a recent patterned ground formation was first described in the cave Skednena jama by Gams (1963). Accumulations due to frost action are now known and described from many cave entrances in Slovenia, especially from higher elevations but also from lower elevations. Examples include caves Potočka zijalka and Snežna jama on Raduha Mountain in the Savinja Alps (Mihevc 2001b), Divje babe (Turk et al. 2001) and Skednena jama in the central part of Slovenia, and Barka rock shelter on the slopes of Snežnik Mountain (Zupan Hajna 2007). In the Barka rock shelter, rock fragments produced by gelifraction are accumulated on the cave floor; in the wintertime freezing causes development of sorted (polygons; Fig. 4.4a, b) and nonsorted patterned ground (Zupan Hajna 2007). Elongated polygons (Fig. 4.4b) are formed where the frost rubble covers the cave floor which is inclined and material may move down the slope due to thawing. In the caves Skednena jama and Ulica pečina, movement of individual marked rocks was measured against the ceiling (Mihevc 2009) and later were compared with Lidar scanograms of the floor. Seasonal vertical displacements due to freezing and thawing were found to be 5–15 cm, and in extreme cases up to 30 cm. Observations show that there are several caves where the cave morphology enhances the periglacial process and sediment creeping and patterned ground formation (Fig. 4.4; Zupan Hajna 2007; Obu et al. 2018), and that freezing causes creeping of the whole sediment body. This can be observed in Bestažovca and Potočka zijalka caves; in both caves these processes interfere with formation of the Palaeolithic and Neolithic archaeological strata (Mihevc 2009) and are still active today. The interior facies develops in those parts of the cave that are more remote from the surface (Fig. 4.1a, b, and d). The

104

M. Blatnik et al.

Fig. 4.4 Polygons of seasonal frost; frost rubble covers the floor and patterned ground are developed (cave shelter in Barka Cave, Mt. Snežnik, SW Slovenia)

composition, mineralogy and lithology of cave clastic sediments depend on the material available in the source areas, but the deposition in the cave depends on the internal dynamics of the conduit system (White 2007). Bosch and White (2004) described facies according to particle size and the degree of sorting as channel, thalweg, slackwater, diamicton, backswamp facies. The channel facies with the widest range of particle size and particle sorting occurs in the most common stream deposits in caves and thalweg facies are the coarse cobbles that form the beds of many active cave streams. Slackwater facies are the thin layers of fine-grained silt and clay forming the final top of clastic deposits. Diamicton facies is the result of debris flows and backswamp facies is locally derived (residual insoluble or infiltrated material). Although we worked with all the types of facies listed during the exploration of sediments in Slovenian caves, slackwater and channel facies were the most represented and dated in our studied cases (e.g. Zupan Hajna et al. 2008a, 2010). Due to the dynamic environment of cave interiors and periodicity of events, sedimentary sequences often represent a series of depositional and erosional events (sedimentary cycles); they are separated by unconformities in which substantial time spans can be hidden (e.g. Bosák et al. 2000b, 2003; Bosák 2002).

4.1.2.2 Infiltrated Sediments By weathering and erosional processes on the surface and percolating water through open fissures and vadose shafts, a lot of different materials (like “terra rossa” or weathered residues of various rocks) can be infiltrated into the karst (Ford and Williams 2007). Mineral composition in such cases depends on the composition of rocks from where the weathering remains originated. Open fissures and shafts

filled with sediments were always of interest to Slovenian researchers (e.g. Šušteršič 1978; Kogovšek and Zupan 1992); their composition and origin were interpreted differently. For a long time, a prevailing opinion was that in all fissures (and also along faults) in karst, red or yellow clays and silts are either “terra rossa” infiltrated into the karst from the surface (Fig. 4.1c), infiltrated eolian deposits, or remains of flood sediments in underground open fissures or cavities. All of the sediment types listed above contain quartz as a dominant mineral among various clay minerals (e.g. Figure 4.5; DHrs). Research of mineral composition of sediments in fissures and fault zones (e.g. Figs. 4.7 and 4.8) has since proven that those are not allochthonous sediments, but tectonic clays formed in situ (Zupan 1989; Zupan Hajna 1997), described in the continuation of this chapter.

4.1.2.3 Allogenic Sediments Major sources of sediments in caves are allogenic sinking streams, bringing sediments into the underground from eroded noncarbonated rocks (Ford and Williams 2007; White 2007). Allogenic cave sediments are particularly important for understanding the environment of their formation before transport and storage in the cave. The same rocks on the surface weather in different ways under different environmental conditions (T, amount of precipitation, pH, Eh) (e.g. Zupan Hajna 1992). Different clay minerals are produced and the colour of the product depends on the type of iron minerals and pigment (e.g. hematite, goethite). Allogenic sediments with almost the same mineral composition but differences in colour are found in the Slovenian river caves Postojnska jama (Figs. 4.5 and 4.8) and Škocjanske jame (Fig. 4.8). Most of the clastic cave sediments in SW Slovenian karst originate from weathered remains of Eocene flysch rocks.

4

Significant Findings from Karst Sediments Research

105

Fig. 4.5 Fluvial sediments from Postojnska jama: a yellow and red clay, silt and sand from a relict passage consist of quartz and clay minerals with feldspars in traces; b yellow allogenic sediment laminas

filled in fissure in artificial tunnel. Allogenic sediments in both cases originate from weathered flysch rocks; they differ in colour and age, but are of almost the same mineralogical composition

Allogenic rivers flowing into the caves, such as the Pivka River (which sinks into Postojnska jama) and the Reka River (which sinks into Škocjanske jame), bring the sediments from weathered flysch rocks of the Pivka Basin and Brkini Hills. For example, among fluvial sediments of active, relict and unroofed caves of the active and relict allogenic Reka River, the mineral composition of all studied sediments is very similar (Fig. 4.8, samples SCfl–DFys). In almost all samples relatively equal mineral composition prevailed, indicating the main source was from flysch rocks which were differentially weathered. The samples contained quartz, clay minerals, microcline, plagioclase and heavy minerals (e.g. goethite, tourmaline, rutile), which are typical of Eocene flysch rocks in the Reka River catchment area. The process of flysch transport into the caves continued for a few million years, but the intensity varied over time (Zupan Hajna et al. 2008a, b, 2010, 2017). Large accumulations of allogenic cave sediments having their origin in flysch rocks show that in some period flysch rocks weathered intensively

and the sediments were transported to the existing caves. The erosion of flysch rocks was probably accelerated in the colder climate and due to increased rainfall or/and due to tectonic uplifting of the landscape. Through studies of the mineral composition of alluvial cave sediments, it was also noticed that in many cases a high amount of carbonate clasts was significant (Zupan Hajna 1992, 1998b, 2002). Examples are sediments in the bottom of deep shafts in Alpine caves of the Kanin Plateau (Črnelsko brezno; Fig. 4.8, sample CHs). It was recognized that the origin of the carbonate clasts (clay, silt and sand size) is the selective and incomplete solution of limestones and dolomites of the caves walls where weathered carbonate rocks were eroded by flowing water (Zupan Hajna 2002). The solution is very similar to the subsoil corrosion on the karst surface, except that the carbonate particles are not mechanically eroded and transported. From the presence of undissolved carbonate particles, it can be concluded that the removal of the limestone from its primary place is not

106

always conditioned merely by dissolution, but also by mechanical erosion. The process of the fine-grained carbonate particles formation is explained below.

4.1.2.4 Accumulations of Fine Carbonate Clasts The presence of a soluble residue of incomplete limestone solution is in disagreement with classical theories of karst origin, which predicts that limestone, when affected by an aggressive solution, will dissolve completely. According to these theories, only insoluble residues will remain after carbonate rock has been dissolved. The way in which the carbonate rock is carried away from its primary site depends mostly on its chemical and mineral composition and on the chemical and hydro-mechanical characteristics of the water; water in a karst environment is a natural solvent as well as the erosive and alluvial agent. Rock may be carried away from its primary site in the form of solution or mechanical particles (by means of chemical or mechanical erosion, or in some cases by a combination of both). The literature mentions occurrences of carbonate particles in the suspended load of subterranean streams (Newson 1972) and in trickling percolation water (e.g. Kogovšek and Habič 1981; Kogovšek and Zupan 1992). The suspended particles were attributed to carbonate rock weathering on the surface and the transport of the weathered rock particles through open fissures into the cave. It was also found that clastic sediments could be enriched on calcite or dolomite (e.g. Zupan 1989; Zupan Hajna 1997, 1998b, 2002); those are actually small particles of limestone or dolostone derived from weathered walls of the underground water passages. The content of carbonate minerals in allochthonous material has been presumed to be low but the X-ray analyses and analyses in thin sections have shown that the carbonate content in a lot of samples could increase to high values, from less than 5% to more than 80%. The proportion of carbonates in cave sediments may increase with the depth of the cave, and dolomite clasts may occur where a cave is formed in dolomite beds. Weathered cave walls present the source for the carbonate grains found in cave sediments due to incomplete dissolution of carbonate rock (Zupan Hajna 2002). The weathered part of limestone is almost identical to the parent rock in its mineral and chemical composition, yet it is much more porous. In limestone different degrees of weathering are seen. Weathered zones pass from wholly weathered limestone to unweathered limestone one through few steps of weathering. Fresh limestone first becomes slightly discoloured and, after weathering progresses, becomes totally discoloured (white) and porous (Fig. 4.6a, b). Ions such as Mg2+ and Sr2+ are leached from the calcite structure, so the calcite is purified during the weathering. In this case, it is not going on to the dissolution of the limestone and then precipitation of cleaner calcite crystals. Weathered

M. Blatnik et al.

limestone becomes more and more porous and develops a “sponge-like” texture. When weathered limestone is wet, the water is in its pores. If there is no source of moisture, the weathered wall of the cave becomes dry. Mechanical erosion takes place where weathered carbonate rock is in contact with flowing or dripping water (Fig. 4.6c). After weathered carbonate rocks are eroded, transportation and accumulation of carbonate particles as cave clastic sediments begin. Water washes the exposed particles from the wall, carries them away and finally accumulates them in the cave sediment in particle sizes ranging from clay, silt or fine sand (Fig. 4.6d). Carbonate particles are deposited either as independent sediments or they may mix with the allochthonous deposits. The result is the production of carbonate fines (silt and clay size particles) which accumulate as autochthonous clastic cave sediments (Zupan Hajna 1998a, 2002).

4.1.2.5 Tectonic Clays Very high contents of carbonate minerals can be detected in tectonic clays if they were formed in fault zones situated in carbonate rocks. This clay size material is formed by tectonic compression of carbonate rocks. Tectonic clay consists almost entirely of calcite or dolomite. Their admixture depends on mineral composition of the parent rocks. Studies of materials from selected locations found that red clays/silts often were actually tectonic clays (mylonite, cataclastite) of the inner fault zones, with mineral compositions mostly of calcite in clay or silt size clasts (or dolomite; depending on the parent rock) where clay minerals, goethite and hematite, were present only in traces (Zupan 1989; Zupan Hajna 1997). Tectonic clay develops in limestone due to cataclastic deformation such that under pressure the limestone recrystallizes and becomes more porous, especially close to the active fault plane. Directly at the fault a collapse of solid limestone structure appears. At first, solution occurs on the borders of the grains; later sparitic grains collapse and soft, unconsolidated clay occurs. Due to its origin, controlled by tectonic pressures, it is called tectonic clay. This term is not yet entirely clear, as occasionally in literature the expression “mylonite” is used for technical crushed rock. Tectonic clays may be either yellow or red in colour. Goethite gives the clay a yellow colour, while a red colour is due to hematite present in the places where the water had been squeezed out of goethite and it was transformed into hematite. This clay impedes drainage within the fault zone. This is why no karstification was recorded in such fault zones. 4.1.2.6 Colour, Mineral Composition and Origin The colour of sediments depends on their mineral composition, the presence of various pigments, and on physical and

4

Significant Findings from Karst Sediments Research

107

Fig. 4.6 a Weathered limestone on cave wall in Martinska jama; b process of weathering and incomplete solution in the cave; c mechanical erosion of exposed limestone or dolomite particles (1.

fresh limestone, 2. weathered limestone); d accumulation of dolomite clasts (silt size) in Renejevo brezno shaft (photo M. Blatnik)

chemical conditions in the environment. But the same colour of sediments doesn’t mean that the same mineral composition and knowledge of the mineral composition is not enough to declare the origin of the clastic sediments. This is because at the end of the weathering only the most resistant minerals, and also the distinctive secondary minerals for certain environments, are present, which reflect the diagenesis of mechanical sediments in the cave. The sediments’ colour in Slovenia includes all varieties from grey, yellow to red and brown. Red colour is usually linked to mineral hematite and thus to oxidation processes, while yellow and grey colours are controlled by humid and reduction conditions within the environment and black by organic matter.

The mineral composition of cave mechanical sediments does not reflect just the climatic conditions at the time of their deposition in caves but also reflects the mineral composition of the original rocks. However, it is not always possible to determine the original rock due to long lasting weathering which may disintegrate a lot of the primary minerals. Heavy minerals are very important for determining origin because they are resistant to weathering and transport due to their mechanical and chemical properties. It is easiest to determine the origin of cave mechanical sediments when their composition entirely reflects the mineral association of the original rock. Quartz is a very resistant mineral in respect to weathering and transport and because of this quartz may be

108

detritus of weathering of various rocks, and its presence does not tell much. In Slovenian caves, different types of fine-grained clastic material may be distinguished based on their origin (Fig. 4.8). From the original rock to the mechanical sediment in the cave, minerals can be lost or changed. The cave allogenic deposits are clastic materials brought into the caves by sinking rivers, where their composition corresponds to the rock composition of the water flow watershed (catchment). In SW Slovenia, they most often are weathered remains of Eocene flysch rocks (Zupan Hajna 1992, 1998a, b, 2000, 2005; Zupan Hajna et al. 2017) which were brought into the caves through a few million years time span. The final products of flysch weathering are most often quartz, various clay minerals and iron minerals; both groups of minerals, however, reflect the environment of original rock weathering. Figure 4.8 (samples SCfl, DCys, Tys, Trc, DFys, PRyl, DHys, DOys, PCfl) shows examples of the mineralogical composition of allogenic cave sediment samples brought into the caves by allogenic rivers from flysch catchments. In all cases quartz prevails; besides clay minerals, microcline and plagioclase are also present, reflecting the original component of flysch rocks in SW Slovenia. Clay minerals differ due to the environmental conditions on the surface during weathering. However, at the end of cave existence, cave sediments may come into the contact with the surface due to the denudation of the karst surface; as a consequence, original cave sediments may be found on the karst surface in unroofed caves (samples PRyl, DHys) or even in the bottom of dolines (samples DOys, DOrs). The infiltrated material is brought into the open fissures and caves from the surface (Fig. 4.1c). Mineral composition in that case depends on composition of rocks and soils from where the weathering remains originated; usually most red soils originated from flysch residue or other surface sediments were brought into the caves as infiltrated material (Fig. 4.8; samples Trc, DHrs and DOrs) and are usually red in colour due to oxidation of iron minerals in them. Clastic material consisting of autochthonous carbonate particles of various sizes originating from cave walls are rare, but may be found in various caves where incomplete solution of cave walls is present (e.g. Figs. 4.6 and 4.8, sample CHs). Silt- and clay-sized clastic carbonate sediments may be found in caves as an addition to allogenic sediments or they may accumulate as autochthonous sediments (Fig. 4.6d) in the cave depositional environment. Sometimes cave passages may cut the fault zone(s) full of cataclastic material, which is significant for the inner part of fault zones (Fig. 4.7). Clay or larger-sized material, formed by tectonic compression of carbonate rocks (limestone or dolomite), consists mainly of calcite or dolomite (Fig. 4.8, sample PCtc).

M. Blatnik et al.

4.1.3 Important Palaeontological Findings Palaeontological material in caves can belong to cave animals that lived in caves and their skeletons are preserved in the conservative environment. More common are remains of surface animals which used caves as dwellings, were washed in, or fell into vertical cave entrances. Remains of fossil cave animals have been found in several caves in Slovenia. The most important is the discovery of the fossil aquatic cave animal Marifugia cavatica (Fig. 4.9) in two locations. The first is located in SW Slovenia where a sediment-filled cave was exposed by the Črnotiče Quarry operations (Mihevc 2000). In the cave filled by allogenic sediments, the calcareous tubes of Marifugia were found both in fine fluvial sediment and also in original positions attached to the cave wall. Sediments were dated by small mammal faunal remains present in sediments and by palaeomagnetic dating method to about 1.8–2.2 Ma (Mihevc et al. 2002; Horáček et al. 2007; Bosák et al. 2004). The animal lived in a cave river that later filled the cave with sediments. At present, Marifugia cavatica lives in spring caves which are about 400 m below and 3 km away from the quarry. The second locality with Marifugia cavatica is the relict cave Velika Pasica in the Central part of Slovenia, which is located about 300 m above the present underground water level. Broken-off tubes were found in the coarse fluvial sediment that is preserved in some parts of the cave. The sediment was dated by fossil mammal remains to about 2 Ma (Mihevc et al. 2017). In both cases, remnants of Marifugia give important information about former elevation of karst water levels and younger relief evolution. Fossil remnants of invertebrates, some of them most likely cave animals, were found in clay layers in the caves Trhlovca and Račiška pečina (Moldovan et al. 2011). Their age was defined by position in the sediment profile position by palaeomagnetic dating to Pre-Qaternary (Zupan Hajna et al. 2010). Cave bear (Ursus spelaeus; Fig. 4.2d) remains are the most abundant Pleistocene fossil mammals in Slovenia; findings were documented in over 90 caves. The most complete dating of them was done on the Divje Babe I. site where cave bear remains (Ursus spelaeus s.l.) were dated (14C and ESR) from 40 to 115 Ka (Turk 2007). Fossil remains of small mammals were found in several Slovenian caves or karst fillings (Aguilar et al. 1998; Sigé et al. 2003). A quarry at Črni kal cut an infilled shaft with large Pleistocene fauna and in Pirešica Quarry small passages filled with sediments revealed small mammals. Among them was an extinct species of dormouse—Glis sp. (Aguilar and Michaux 2011; Sigé et al. 2003). Those palaeontological findings helped to calibrate the palaeomagnetic results of studied sediment sections in Črnotiče Quarry and Račiška

4

Significant Findings from Karst Sediments Research

109

Fig. 4.7 a Tectonic clay from a fault zone in Pivka jama (Postojnska jama); b tectonic clay at fault plane; it consists almost 100% of calcite particles of silt and clay size (Fig. 4.5). The colour is the same as

allogenic flood loam brought into the cave by river (in Fig. 4.5b), but the mineral composition is different

Fig. 4.8 Comparison of selected cave sediment sample mineralogical compositions originating from underground Reka and Pivka rivers, fault zone in Pivka jama and from the Alpine cave Črnelsko brezno, Slovenia. Legend: SCfl Škocjanske jame recent flood loam; DCys Divaška jama relict laminated yellow sand; Tys Trhlovca relict yellow sand; Trc Trhlovca red clasts; DFys Divača relict yellow sand and clay; PRyl Povir (roofless cave) yellow loam; DHys Divaški hrib (relict filled cave) yellow sand; DHrs (relict filled cave) infiltrated red sediment;

DOys Divača 1 (doline) yellow sediment; DOrs Divača 1 (doline) red sediment; PCfl Pivka jama (active cave) flood loam; PCtc Pivka jama (fault zone) tectonic clay; CHs Črnelsko brezno (deep shaft) clastic sediment; Q quartz; Ca calcite; D dolomite; Mu/IL muscovite/illite minerals; Ka kaolinite; Cl chlorite; Mo montmorillonite group of minerals; Mi microcline; Pl plagioclase; Gi gibbsite; G goethite; T tourmaline; Ru rutile

110

M. Blatnik et al.

Fig. 4.9 Tubes of Marifugia cavatica on the unroofed cave in Črnotiče Quarry

pečina and Snežna jama caves. For the first time in Slovenia, biostratigraphic data helped to correlate magnetostratigraphy logs with the GPTS and to allocate the ages of cave fill more precisely to pre-Quaternary times (Horáček et al. 2007). Palaeontological finds in the Račiška pečina and Črnotiče Quarry confirmed the age interpreted from magnetostratigraphy. Cave fills are often Pliocene in age and even older (Zupan Hajna et al. 2008a, 2010).

4.1.4 Age of Cave Sediments The first studies of cave sediments in Slovenia were carried out during archaeological and palaeontological excavations of sediments in cave entrances (e.g. Brodar 1952, 1966) where they interpreted all sediments with alternation of cold and warm periods during Pleistocene, disintegration of cave walls and the sliding of the slope materials into the cave. Detailed studies of cave sediments were later done by Gospodarič (1972, 1976, 1981, 1988) in the 70s and 80s of the last century. Gospodarič (1988) applied a relative dating method, comparing cave sediments from different sites to establish the age of deposits and also used available dating methods. He suspected that the cave sediments were not much older than 350 Ka, although it has been already noted that some dating results were beyond this time. In his geochronology of cave sediments based on recognition and descriptions of several profiles from various caves, he classified different deposition phases in the subsurface and linked them to sea-level oscillations and climate changes during the Pleistocene (Franke and Geyh 1971; Ikeya et al. 1983; Ford and Gospodarič 1989). In the Kras region (SW Slovenia), Gospodarič (1988) linked the karstification of the area with glacio-eustatic oscillations of the Adriatic Sea and the global palaeoclimate evolution during the Pleistocene.

Later U-series dating indicated that speleothems from different caves in Slovenia must be older (Zupan 1991; Zupan Hajna 1996; Mihevc and Lauritzen 1997; Mihevc 2001a). Results indicated that speleothem growth corresponded to warmer periods during the Pleistocene; but nevertheless there were large numbers of speleothems older than the limit of the method (350 Ka in the 1990s). These results proved that the cave sediments were older than had been previously thought. The application and interpretation of palaeomagnetic analysis and magnetostratigraphy of cave sediments, both clastic and chemogenic, which began in 1997, suggested substantial changes in the lower limiting ages of cave fill deposition (e.g. Bosák et al. 1998, 1999, 2000a, b, 2002, 2004; Šebela and Sasowsky 1999, 2000; Audra 2000; Mihevc et al. 2002; Horáček et al. 2007; Zupan Hajna et al. 2008a, b, 2010; Knez et al. 2016). Systematic studies of cave sediments in Slovenian caves in the last 20 years using different dating methods showed that the sediments were much older than had been originally assumed, as the identified ages cover not only the entire periods of the Pleistocene and Pliocene but also reach into the Miocene. In SW Slovenia, in the area of the Classical Karst, the last evidence of marine sedimentation exists since the Eocene, when flysch sediments were deposited. Palaeomagnetic dating in combination with other methods, especially U-series dating and biostratigraphy, have shifted the possible beginning of cave infilling processes and speleogenesis in Slovenia below the Tertiary/Quaternary boundary. Sediment sections from about 30 studied caves were divided into segments according to palaeomagnetic polarity, NRM, MS, lithology and age. Mean palaeomagnetic declination and inclination were then calculated for each segment (Vrabec et al. 2018). Where possible, age determination was augmented with absolute ages obtained from speleothems

4

Significant Findings from Karst Sediments Research

interbedded with or covering the sediments, and with biostratigraphical (Horáček et al. 2007) or archaeological data. We found that cave sediments were predominantely deposited in three distinct episodes: 5.4–4.1 Ma, 3.6–1.8 Ma, and 0.78 Ma–present, reflecting regional-scale environmental and tectonic forcing (Zupan Hajna et al. 2010) as the cessation of Miocene deposition in the Pannonian Basin in the Central, E and SE Slovenia and post-Messinian evolution in the SW and W Slovenia. These sedimentation phases in the underground suggest climatic changes on the surface with possible flood events and/or changes of the tectonic regimes during Neogene and Quaternary. It was also evident that all studied sediments were deposited within one post-Eocene karstification period. However, since the processes of sedimentation in the caves are very complex and strongly influenced by local factors, with sediment profile thicknesses of usually only a few metres and interrupted by several unconformities, the interpretation of cave sediments and the resulting data of the surface and subsurface processes is very complex. Calibrated data contributed to reconstruction of the speleogenesis, deposition in caves, and indirectly to evolution of karst surfaces and succession of tectonic displacements (Häuselmann et al. 2015; Vrabec et al. 2018; Zupan Hajna et al. 2017). The research of cave sediments has not been finished yet; the interpretation of obtained data regarding tectonic, climate, geomorphological and speleological evolution of specific karst areas is in progress.

References Aguilar JP, Michaux J (2011) Pleistocene edible dormice (Rodentia Mammalia) from Slovenia, and their relations to the present day Glis Glis (Linnaeus 1766). Acta Carsolog 40(2):369–380 Aguilar JP, Crochet JY, Krivic K, Marandat B, Michaux J, Mihevc A, Sigé B, Šebela S (1998) Pleistocene small mammals from some karstic fillings of Slovenia—preliminary results. Acta Carsolog 27 (2):141–150 Audra P (2000) Le karst haut alpin du Kanin (Alpes Juliennes, Slovénie–Italie). État des connaissances et données récentes sur le fonctionement actuel et l´évolution plio-quaternaire des structures karstiques. Karstologia 35:27–38 Bosák P (2002) Karst processes from the beginning to the end: how can they be dated? In: Gabrovšek F (ed) Evolution of karst: from prekarst to cessation. Carsologica, Založba ZRC, Postojna-Ljubljana, pp 191–223 Bosák P, Pruner P, Zupan Hajna N (1998) Palaeomagnetic research of cave sediments in SW Slovenia. Acta Carsolog 27(2):151–179 Bosák P, Mihevc A, Pruner P, Melka K, Venhodová D, Langrová A (1999) Cave fill in the Črnotiče Quarry, SW Slovenia: Palaeomagnetic, mineralogical and geochemical study. Acta Carsolog 28 (2):15–39 Bosák P, Knez M, Otrubová D, Pruner P, Slabe T, Venhodová D (2000a) Palaeomagnetic research of a fossil cave in the highway construction at Kozina, SW Slovenia. Acta Carsolog 29(2):15–33

111 Bosák P, Pruner P, Mihevc A, Zupan Hajna N (2000b) Magnetostratigraphy and unconformities in cave sediments: case study from the Classical Karst, SW Slovenia. Geologos 5:13–30 Bosák P, Hercman H, Mihevc A, Pruner P (2002) High resolution magnetostratigraphy of speleothems from Snežna Jama, Kamniške-Savinja Alps, Slovenia. Acta Carsolog 31(3):15–32 Bosák P, Pruner P, Kadlec J (2003) Magnetostratigraphy of cave sediments: Application and limits. Stud Geophys Geod 47(2):301– 330 Bosák P, Mihevc A, Pruner P (2004) Geomorphological evolution of the Podgorski Karst, SW Slovenia: Contribution of magnetostratigraphic research of the Črnotiče II site with Marifugia sp. Acta Carsolog 33(1):175–204 Bosch RF, White WB (2004) Lithofacies and transport of clastic sediments in karstic aquifers. In: Sasowsky ID, Mylroie JE (eds) Studies of cave sediments. Springer Science & Business Media, pp 1–22 Brodar S (1952) Prispevek k stratigrafiji kraških jam Pivške kotline, posebej Parske golobine. Geogr vestn 24:43–76 Brodar S (1966) Pleistocenski sedimenti in paleolitska najdišča v Postojnski jami. Acta Carsolog 4:57–138 Brodar S, Brodar M (1983) Potočka zijalka: visokoalpska postaja aurignacienskih lovcev (Zusammenfassung: Potočka zijalka: eine hochalpine Aurignacjägerstation). Dela SAZU 24, p 213 Culiberg M, Kaligarič M, Lovrenčak F, Seliškar A, Zupančič M (1997) 8. Soil & Vegetation. In: Kranjc A (ed) Kras: Slovene classical Karst. Ljubljana, pp 103–129 Durn G (2003) Terra rossa in the Mediterranean region: parent materials, composition and origin. Geologia Croatica 56(1):83–100 Fedoroff N, Courty MA (2014) Revisiting the genesis of red Mediterranean soils. Turk J Earth Sci 22(3):359–375. https://doi. org/10.3906/tar-1210-89 Ford DC, Gospodarič R (1989) U series dating studies of Ursus spelaeus deposits in Križna jama, Slovenia. Acta Carsolog 18:39–51 Ford DC, Williams PW (2007) Karst hydrogeology and geomorphology. Wiley, Chichester, p 562 Franke H, Geyh M (1971) 14C – Datierungen von Kalksinter aus slowenischen Höhlen. Der Aufschluss 22:235–237 Gams I (1963) Logarček. Acta Carsolog 3:7–84 Gams I (1974) Kras (Karst). Slovenska matica, Ljubljana, p 359 (in Slovene language) Gams I (2004) Kras v Sloveniji v prostoru in času. Založba ZRC, Ljubljana, p 516 (in Slovene language) Gospodarič R (1972) Prvi podatki o absolutni starosti sige v Postojnski jami na podlagi 14C. Naše jame 13:91–98 Gospodarič R (1976) Razvoj jam med Pivško kotlino in Planinskim poljem v kvartarju (summary: The Quaternary caves development between the Pivka Basin and Polje of Planina). Acta Carsolog 7:8– 135 Gospodarič R (1981) Generations of speleothems in the Classical Karst of Slovenia. Acta Carsolog 9:90–110 Gospodarič R (1988) Palaeoclimatic record of cave sediments from Postojna karst. Annales de la Société Géologique de Belgique 111:91–95 Gregorič V (1967) Minerali glin v nekaterih talnih enotah Slovenskega primorja. Geologija 10:247–270 Gregorič V (1969) Nastanek tal na triadnih dolomitih. Geologija 12:201–230 Grund A (1914) Der geographische Zyklus im Karst. Geschichte der Erdkunde 52:621–640 Habič P (1992) Les phénomènes paléokarstiques du karst Alpin et Dinarique en Slovénie. In: Salomon JN, Maire R (eds) Karst et évolutions climatiques. Presses Universitaires de Bordeaux, Bordeaux, pp 411–428

112 Häuselmann P, Mihevc A, Pruner P, Horáček I, Čermák S, Hercman H, Sahy D, Fiebig M, Zupan Hajna N, Bosák P (2015) Snežna jama (Slovenia): Interdisciplinary dating of cave sediments and implication for landscape evolution. Geomorphology 247:10–24 Horáček I, Mihevc A, Zupan Hajna N, Pruner P, Bosák P (2007) Fossil vertebrates and palaeomagnetism update one of the earlier stages of cave evolution in the Classical Karst, Slovenia: Pliocene of Črnotiče II site and Račiška pečina. Acta Carsolog 37(3):451–466 Hrovat A (1953) Kraška ilovica. Ljubljana, p 91 (in Slovene language) Ikeya M, Miki T, Gospodarič R (1983) ESR dating of Postojna Cave stalactite. Acta Carsolog 11:117–130 Jurkovšek B, Toman M, Ogorelec B, Šribar L, Drobne K, Poljak M (1996) Formacijska geološka karta 1:50.000 južnega dela Tržaško-Komenske planote/Geological map of the southern part of the Trieste—Komen plateau 1:50,000. Cretaceous and Palaeogene carbonate rocks. Inštitut za geologijo, geotehniko in geofiziko, Ljubljana, p 143 Knez M, Slabe T (eds) (2016) Cave Exploration in Slovenia: discovering over 350 new caves during motorway construction on classical karst (Cave and karst systems of the world). Springer, Cham, p 324 Kogovšek J, Habič P (1981) Preučevanje vertikalnega prenikanja vode na primerih Planinske in Postojnske jame. Acta Carsolog 9:129–148 Kogovšek J, Zupan N (1992) Prenos trdnih delcev pri vertikalni cirkulaciji v krasu. Naše jame 34:13–19 Melik A (1961) Fluvialni elementi v krasu. Geografski zbornik 6:333– 361 Mihevc A (1996) Brezstropa jama pri Povirju. Naše jame 38:92–101 Mihevc A (2000) The fossilized tubes from the roofless cave – probably the oldest known remains of the cave worm Marifugia (Annelida: Polychaeta). Acta Carsolog 29(2):261–270 Mihevc A (2001a) Speleogeneza Divaškega krasa./The Speleogenesis of the Divača Karst. Zbirka ZRC 27, Ljubljana, p 180 (in Slovene language) Mihevc A (2001b) Jamski fluvialni sedimenti v Snežni jami na Raduhi in v Potočki zijalki. In: Horvat A (ed) Abstracts of papers, Geološki zbornik 16:60–63 Mihevc A (2007) The age of karst relief in West Slovenia. Acta Carsolog 36(1):35–44 Mihevc A (2009) Cryoturbation of the sediments at the cave entrances: case studies from Skednena jama, Potočka zijalka and Bestažovca Cave. In: Steguweit L (ed) Hugo Obermaier Society for Quaternary Research and Archaeology of the Stone Age, Hugo Obermaier-Gesellschaft für Erforschung des Eiszeitalters und der Steinzeit, 51st Annual Meeting in Ljubljana, 14–18 April, 2009. [Erlangen]: Hugo Obermaier-Gesellschaft für Erforschung des Eiszeitalters und der Steinzeit., pp 26 Mihevc A, Lauritzen SE (1997) Absolute datations of speleothems and its speleomorphological significance from Divaška jama and Jazbina caves; Kras plateau, Slovenia. In: Proceedings of the 12th international congress of speleology, La Chaux-de-Fonds, Switzerland. Speleo Projects 1, Basel, pp 57–59 Mihevc A, Zupan Hajna N (1996) Clastic sediments from dolines and caves found during the construction of the motorway near Divača, on the classical Karst. Acta Carsolog 25:169–191 Mihevc A, Bosák P, Pruner P, Vokal B (2002) Fosilni ostanki jamske živali Marifugica cavatica v brezstropi jami v kamnolomu Črnotiče v zahodni Sloveniji. Geologija 45(2):471–474 Mihevc A, Brancelj A, Horáček I (2017) Use of the cave animal Marifugia cavatica for reconstruction of Pliocene to recent evolution of karst relief in W Slovenia. In: Moore K, White SQ (eds) Proceedings of the 17th International Congress of Speleology, Sydney, NSW, Australia, July 22–28, 2017, Vol. 2. Australian Speleological Federation, Sydney, pp 65–68

M. Blatnik et al. Moldovan O, Mihevc A, Miko L, Constantin S, Meleg I, Petculescu A, Bosák P (2011) Invertebrate fossils from cave sediments: a new proxy for pre-Quaternary palaeoenvironments. Biogeosciences 8 (7):1825–1837 Newson MD (1972) Merits of a hydrogeological bias to karst erosion studies. Trans Cave Research Group of Great Britain 14(2):118–124 Obu J, Košutnik J, Overduin P, Boike J, Blatnik M, Zwieback S, Gostinčar P, Mihevc A (2018) Sorted patterned ground in a karst cave Ledenica pod Hrušico, Slovenia. Permafrost and periglacial processes 29(2):121–130 Radinja D (1972) Zakrasevanje v Sloveniji v luči celotnega morfogenetskega razvoja. Geografski zbornik 13:197–243 Radinja D (1986) The Karst in the light of fossilized fluvial deposition. Acta Carsolog 14–15:101–108 Rejšek K, Vranova V, Formanek P (2012) Determination of the proportion of total soil extracellular acid phosphomonoesterase (E. C. 3.1.3.2) activity represented by roots in the soil of different forest ecosystems. Sci World J 2012, available online Roglić J (1957) Zaravni u vapnencima. Geografski glasnik 19:103–134 (in Croatian language) Sigé B, Mihevc A, Aguilar JP (2003) Les chiroptères actuel et fossils. Recent and late Pleistocene bats in a mountain cave of Slovenia: evidence of a climatic drop. Coloquios de palaeontología 1:637–645 Šebela S, Sasowsky I (1999) Age and magnetism of cave sediments from Postojnska jama cave system and Planinska jama Cave. Slovenia. Acta Carsolog 28(2):293–305 Šebela S, Sasowsky I (2000) Palaeomagnetic dating of sediments in caves opened during highway construction near Kozina, Slovenia. Acta Carsolog 29(2):303–312 Šušteršič F (1978) Nekaj misli o zasutih breznih in njihovem polnilu. Naše jame 19:7–14 Šušteršič F, Rejšek K, Mišič M, Eichler F (2009) The role of loamy sediment (terra rossa) in the context of steady karst lowering. Geomorphology 106(1–2):34–45 Turk I (ed) (2007) Divje babe I, Upper Pleistocene Palaeolithic site in Slovenia, Part 1: Geology and Palaeontology. Opera Instituti Archaeologici Sloveniae 13, Ljubljana, p 478 Turk I, Skaberne D, Blackwell B, Dirjec J (2001) Morfometrična in kronostratigrafska analiza ter palaeoklimatska razlaga jamskih sedimentov v Divjih babah I, Slovenija. Arheološki vestnik 52:221–247 Vrabec M, Pruner P, Zupan Hajna N, Mihevc A, Bosák P (2018) Unraveling neotectonic vertical-axis rotations in the Adria-Eurasia collision zone: palaeomagnetic data from Pliocene-Quaternary cave sediments (Slovenia). In: Ustaszewski K, Grützner C, Navabpour P (eds) TSK Jena 2018, 1st ed. Friedrich Schiller University Jena, Institute of Geological Sciences, Jena, p 134 White WB (2007) Cave sediments and palaeoclimate. Journal of Cave and Karst Studies 69(1):76–93 Zupan N (1989) Mineralogija tektonske gline v Pivki jami/Mineralogy of tectonic clay in Pivka jama. Acta Carsolog 18:141–156 Zupan N (1991) Flowstone datations in Slovenia. Acta Carsolog 20:187–204 Zupan Hajna N (1992) Mineral composition of mechanical sediments from some parts of Slovenian karst. Acta Carsolog 21:115–130 Zupan Hajna N (1996) The valuation of absolute speleothem dating from Slovenia. In: Lauritzen S-E (ed) Climate change: The Karst record: extended abstracts of a conference held at Department of geology University of Bergen, Norway, 1–4 August 1996 (Special Publication 2). Karst Waters Institute, Charles Town, pp 185–188 Zupan Hajna N (1997) Mineral composition of clastic material in fault zones and open fissures in karst rocks, examples from SW Slovenia. Proceedings of the 12th International Congress of Speleology, La Chaux-de-Fonds 2, pp 33–36

4

Significant Findings from Karst Sediments Research

Zupan Hajna N (1998a) Mineral composition of clastic sediments in some dolines along the new motorway Divača-Kozina. Acta Carsolog 27:277–296 Zupan Hajna N (1998b) Mineral composition of clastic cave sediments and determination of their origin. Kras i speleologia 9(18):169–178 Zupan Hajna N (2000) Some ideas about the origin, diagenesis and time of sedimentation of clastic sediments from the karst surface and caves around Divača, SW Slovenia. In: Vlahović I, Biondić R (eds) 2. hrvatski geološki kongres, Cavtat–Dubrovnik, Zbornik radova. Institut za geološka istraživanja, Zagreb, pp 489–493 Zupan Hajna N (2002) Origin of fine-grained carbonate clasts in cave sediments. Acta Carsolog 31(2):115–137 Zupan Hajna N (2005) Clastic sediments and soils on the Kras. In: Mihevc A (ed) Kras: water and life in a rocky landscape. Založba ZRC, Ljubljana, pp 37–43 Zupan Hajna N (2007) Barka depression, a denuded shaft in the area of Snežnik Mountain, Southwest Slovenia. J Caves Karst Stud 69 (2):266–274

113 Zupan Hajna N, Mihevc A, Pruner P, Bosák P (2008a) Palaeomagnetism and Magnetostratigraphy of Karst Sediments in Slovenia. Carsologica 8, Založba ZRC, Ljubljana, p 266 Zupan Hajna N, Mihevc A, Pruner P, Bosák P (2008b) Cave sediments from the Postojnska-Planinska cave system (Slovenia): evidence of multiphase evolution in epiphreatic zone. Acta Carsolog 37(1):63– 86 Zupan Hajna N, Mihevc A, Pruner P, Bosák P (2010) Palaeomagnetic research on karst sediments in Slovenia. Int J Speleol 39(2):47–60 Zupan Hajna N, Mihevc A, Pruner P, Bosák P (2017) Cave sediments in Škocjanske Jame and unroofed caves above them, SW Slovenia. In: Moore K, White SQ (eds) Proceedings of the 17th International Congress of Speleology, Sydney, July 22–28, 2017, Vol. 2. Australian Speleological Federation, Sydney, pp 34–36 Zupan Hajna N, Otoničar B, Pruner P, Culiberg M, Hlaváč J, Mandić O, Skála R, Bosák P (2019) Late Pleistocene lacustrine sediments and their relation to red soils in the Northeastern margin of the Dinaric karst. Acta Carsolog 48(2):153–171

5

Measurements of Present-Day Limestone Dissolution and Calcite Precipitation Rates with Limestone Tablets in Stream Caves (with the Case Study of Škocjanske Jame) Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna Quantification of present-day fundamental chemical processes in caves (dissolution and calcite precipitation) can provide basic objective information on rates, make possible comparison with other speleogenetic processes, and provide insights into spatial and temporal variability as well as factors controlling both processes. Comparison of theoretical rate-based morphology with the observed (actual) one can help to differentiate active and relict morphology in caves. Although the factors that control rate of dissolution and calcite precipitation can change significantly during speleogenesis, dissolution rates provide at least a rough estimate of the time needed for cave formation―an issue that is a significant result of speleogenetic modelling and indirectly targeted by datation of cave sediments. The one widely accepted methodology for measurement of cave wall retreat is use of a micro (erosion) meter (MEM) that takes into account sum of all processes affecting cave wall retreat. However, one of the most significant drawbacks of measurement of present-day processes is the small rates (Prelovšek 2012) that are also indicated by the high ages of cave sediments (Zupan Hajna et al. 2008). While the precision and accuracy of MEM significantly improved in recent decades and what was once analogue has become digital, MEM’s tip (probe) erosion as a result of M. Blatnik
F. Gabrovšek
M. Knez (&)
B. Kogovšek
J. Kogovšek
C. Mayaud
A. Mihevc
J. Mulec
M. Năpăruş-Aljančič
B. Otoničar
M. Petrič
T. Pipan
M. Prelovšek
N. Ravbar
T. Shaw
T. Slabe
S. Šebela
N. Zupan Hajna Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia e-mail: [email protected] D. C. Culver American University, Washington, DC, USA H. Liu Yunnan University, Kunming, China

contact with the partially weathered rock surface still presents severe problem with regard to the desired micrometre scale of measurement. Until precise field non-contact MEM measurements are accessible, the use of the hydrochemical method and limestone tablets are recognized as the most precise methodologies to target small dissolution and calcite precipitation rates. While the hydrochemical method, where specific electrical conductivity or water hardness can be compared upstream and downstream along underground stream passages without tributaries, can be an alternative approach for the detection of dissolution or calcite precipitation rates; the use of limestone tablets is more comparable to that of MEM. The main benefit of this approach is a much more accurate measurement of weight loss (or gain) instead of the less accurate measurement of distance that is obtained with MEM. Taking into account the density of limestone used for limestone tablets and reaction surface, one can convert weight loss/gain into metric units, i.e. mm/a. However, one has to take into account that different approaches result in slightly different rates (Prelovšek 2012); some less known processes that might contribute to total dissolution (e.g. biodissolution) might be partly or completely excluded when limestone tablets are used for short periods. The purpose of this chapter is a general presentation of measurement with limestone tablets that have been intensively used and tested from 2004 onwards, mainly in the Classical Karst area. Special emphasis is given to Škocjanske jame (Škocjan Caves) where this approach faces several methodological challenges (transport of cobble, sand and silt in suspension, discharge over 250 m3/s, deposition of clay). Additionally, Škocjanske jame is a well-studied area where the results of measurements with limestone tablets can be compared by hydrochemical as well as morphological observations. This provides important additional data for interpretation of measured rates, as well as independent

© Springer Nature Switzerland AG 2020 M. Knez et al. (eds.), Karstology in the Classical Karst, Advances in Karst Science, https://doi.org/10.1007/978-3-030-26827-5_5

115

116

M. Blatnik et al.

information on present-day rates that have been used to test the reliability of the methodology. Similar approach where hydrochemical data were compared with dissolution rate measured by limestone tablets at two springs in Arkansas (USA) was used by Covington and Vaughn (2018).

5.1

Standard Limestone Tablets, Preparation, Mounting, Weighing, Precision and Accuracy

Besides the first trials to measure dissolution rates with limestone tablets in caves (Chevalier 1953 after Gams 1959; Rebek 1964), the first intensive as well as global use of limestone tablets for determination of dissolution rates is related to Gams (1985). He prepared hundreds of tablets made of limestone from the Lipica quarry (Classical Karst) and sent them over several continents to observe differences in soil and atmospheric dissolution rates globally. As a result of this global approach, limestone tablets made of the same limestone are considered as “standard limestone tablets”. The detailed chemical composition of this micrite- and biopelmicrite-type of limestone, in which the share of CaCO3 is about 98%, can be found in Gams (1985). While surface area is specific for each limestone tablet since it depends also on the thickness, the density of limestone is considered to be 2.71 kg/m3 (Gams 1985) or 2.69 kg/m3 (Prelovšek 2012). Partial naturalization of the limestone tablet surface as well as elimination of saw dust is achieved by etching―in case of Prelovšek (2012) with 10% solution of HCl for 5 s. Gams (1986) used plastic wires to attach limestone tablets and to observe dissolution or calcite precipitation rates in underground streams. Other types of mounting (nylon cages/bags) with different mesh sizes (Newson 1971;

Jennings 1977 after Jennings 1982; Goudie et al. 1981) can provide additional information about processes responsible for weight loss, e.g. differentiation between dissolution and abrasion. However, all these mounting approaches have some important drawbacks, such as • Inability to overcome highly turbulent streams with high velocity; • Uncertainty over abrasion of the tablet with regard to the material used for mounting, especially when there are variations in weathering and the resulting incomplete dissolution needs to be taken into account; • Abrasion of weakly attached calcite crystals as a result of (temporal) oversaturation of waters. To avoid these issues, Prelovšek (2012) started mounting limestone tablets directly to the wall through a hole drilled into the centre of the tablet (Fig. 5.1a). The initial iron mounting material was later replaced by stainless steel due to the problem of enhanced dissolution under rusting iron. Limestone abrasion caused by the mounting material was prevented with felted washers and tight mounting. Three limestone tablets were used at the same measurement site to get insights into the variability as well as undesired impacts of abrasion and attrition (chipping, polishing; Fig. 5.1a). Limestone tablet pairs were established to observe the temporal variability of dissolution and calcite precipitation at a specific measurement site―one being exposed and another being weighed in a lab and waiting for the next replacement. Damage during transportation was avoided with a specially constructed case in which the limestone tablets were separated and tightly attached to the carrying structure to avoid abrasion while crawling through a cave (Fig. 5.1b). Instead of drying at 110 °C (Gams 1985) to remove pore water, the content of pore water was related to relative humidity;

Fig. 5.1 a Mounting of three limestone tablets on the cave wall and b transport using a specially constructed case

5

Measurements of Present-Day Limestone Dissolution …

according to relative humidity, a correction factor was calculated to improve the accuracy of measurement (Prelovšek 2012). Lithological heterogeneity of standard limestone tablets (e.g. ratio between allochems and micrite, type of allochems, degree of recrystallization) can be problematic during short-term measurements and in environments with low dissolution rates where deviations of up to 1.6 µm per measurement can be expected; however, during long-term measurements or in high-dissolution-rate environments the impact of lithological differences falls to 0.1 µm per measurement (Prelovšek 2012). While comparison of standard limestone tablets with tablets made of other types of Cretaceous and Jurassic limestone developed mostly on the Adriatic-Dinaric carbonate platform shows 10% of standard and up to 20% of maximum deviation, marble and dolomite show much lower dissolution rates, about 30% and up to 90%, respectively (Prelovšek 2012). Comparison of rates measured by limestone tablets and MEM indicate 19% (Jennings 1981 after Spate et al. 1985) or 33% (Prelovšek 2012) lower rates when limestone tablets are used, and this might be related to MEM tip (probe) erosion. As a result, measurements with standard limestone tablets can provide reliable information on wall retreat in caves developed in Cretaceous and Jurassic limestones on the Adriatic-Dinaric carbonate platform; in the case of other rock types, however, caution is needed when rates measured by standard limestone tablets are applied to cave wall retreat.

5.2

Case Study of the Reka River and Škocjanske Jame

Škocjanske jame is an extraordinary example of a cave system developed in a contact karst setting. The cave system is influenced by a high variation of sinking Reka River discharge (1:2,419), highly turbulent flow accompanied by huge transport of bedload as well as suspended material, and flooding. All these factors make dissolution/calcite precipitation measurements with limestone tablets challenging due to issues of mechanical erosion (abrasion, attrition), hydrodynamic pressure, and sedimentation of fine-grained material that can be later cemented by calcite. At the hydrological station Cerkvenikov mlin (0.5 km upstream of the flysch-limestone contact), the Reka River drains water from an approximately 350 km2 catchment area. The highest share of catchment area (60–74%; Brkini Hills) is composed of Eocene rocks represented by marls, siltstone and sandstone, where siliciclastic grains (54–82 wt %; Mikes et al. 2006) are cemented by calcite or quartz. In Brkini Hills, CaO constitutes 0.1–14.8 wt% of unweathered Eocene rocks (Mikes et al. 2006). The rest of the catchment area is composed of karstified carbonate rocks (mainly Cretaceous limestones); from these areas authigenic water is

117

drained toward two larger karst springs that feed the main course of the Reka River. The typical discharge of the Reka River is 8.12 m3/s (Slovenian Environment Agency), the highest measured one in the period 1952–2017 reached 305 m3/s (Slovenian Environment Agency), while the discharge with a recurrence period of 100 years is estimated to be 453 m3/s (Mihevc 2001). Backflooding of up to a documented 132 m (Mihevc 2001) is possible when the discharge exceeds 105–120 m3/s (Gabrovšek, unpublished). The average flux of sediments through Škocjanske jame is estimated to 30,000 m3/a (Kranjc 1986), resulting in mechanical erosion rates of up to −160 µm/a in Škocjanske jame (Mihevc 2001). During measurements with limestone tablets (over almost 13 years), the highest observed discharge reached 279 m3/s (Table 5.2). There are several methodological challenges to use limestone tablets in Škocjanske jame. While care during positioning of measurement sites at places away from the main sediment flow resulted in unbroken limestone tablets during observation at all measurement sites, sediment transport above 60 m3/s resulted in attrition (visible chipping of the tablet’s edge) and possibly abrasion, with the highest rates usually at the ending (most exposed) limestone tablet (Table 5.1 and Fig. 5.5). Attrition was related to bedload transport, since visual mechanical alteration (chipped edges of limestone tablets) was limited only to measurement sites at the bed of a channel and absent some metres above it. Some measurement sites are constantly (measurement site S-6 at Martelovo jezero; Fig. 5.3b and Table 5.1) or temporarily (measurement sites S-1, S-2, S-10, S-11, and S-12) resistant to mechanical damage but, on the other hand, prone to sedimentation, which is usually the highest at the middle of three exposed tablets (see Fig. 5.3b, measurement site S-6). The impact of suspended sediment on weight loss (rate) due to abrasion is not clear, since visual alteration is absent during the mechanical action of fine-grained sediment but it can be expected (Jennings 1982). Due to highly turbulent flow, loose screw tightening resulted in limestone tablet abrasion at the contact with screw. After a high water level, sedimentation was frequently observed either at higher measurement sites (S-4, S-5, S-7, S-8, and S-9) or at measurement sites with calm water (S-6); while the silty sediment was easily removed from higher measurement sites by gentle washing with tap water, lower measurement sites in calm water indicated a severe problem due to interaction of sedimentation of fine-grained sediment with calcite precipitation. Despite gentle washing with soft pressure using nitrile gloves, such washing inevitably removed loosely attached precipitated calcite but, at the same time, was not able to remove strongly cemented fine-grained sediment. High variation of weight gain among three limestone tablets from the same measurement site as a result of fine-grained particles cementation (and higher calcite precipitation rates?)

118

M. Blatnik et al.

can be observed; in such cases, the highest precipitation/sedimentation rates were observed at the middle limestone tablet where the flow rate was the lowest. In addition, precipitation/sedimentation was visually absent at the tablet’s rim, indicating frequent washing of fine-grained sediment and gentle abrasion by silty transported material. While the magnitude of calcite precipitation is probably determined correctly, uncertainty over exact rates, which can vary similarly to variation of mechanical erosion rates as measured by Mihevc (2001), remains.

5.2.1 Results of the Limestone Tablet Measurements Measurement with limestone tablets started on 1 February 2006 with measurement sites S-1 and S-2. Later, the number of measurement points rose to a total of 12 measurement sites (Fig. 5.2). Each replacement of limestone tablets represents an individual measurement period (Table 5.1). The first and the longest observation took place at measurement sites S-1 and S-2 (Swidovo razgledišče (Swida’s Viewpoint); Fig. 5.2 and Table 5.1) where one limestone tablet was used at each site. Tablets were exposed 2 m apart in the middle of an underground channel to water flow with Q > 3 m3/s. Four among six measurement periods reveal a problem with attrition when the discharge exceeded 60 m3/s (Tables 5.1 and 5.2). Visual observation as well as a temporal decline of the weight loss during the last three measurement periods, despite an increase of maximum period discharge (rates in µm/a; Table 5.2), indicate edge chipping (attrition) as the strongest process of mechanical erosion with polishing (abrasion) being less intensive. Small changes during the 1.5-year-long total of the 2nd and 3rd measurement periods, when the result of attrition was visually absent and discharge remained below 60 m3/s, indicated weak processes close to the error of measurement with a tendency toward net calcite precipitation (from +0.1 to +0.3 µm/a). Since mechanical erosion (attrition), when discharge exceeds

60 m3/s, might override dissolution, measurement with limestone tablets was carried out using a vertical arrangement, as detailed below. The vertical arrangement of limestone tablets at Swidovo razgledišče was established on 27 February 2008 and involved three measurement sites from the middle of an underground channel (S-3) and 2.5 m (S-4) as well as 4.9 m (S-5) higher. While the position of S-3 is similar to those of S-1 and S-2, the upper two sites are flooded with discharge of several tens of m3/s (S-4) or about 100 m3/s (S-9). At each measurement site three limestone tablets were used to increase precision and to get better insight into potential mechanical erosion. The lowest measurement site (S-3) was useless for dissolution/calcite precipitation measurement due to chipping, even at a discharge of 0.5, pCO2 (SICal=0) is probably higher than the calculated value due to prior calcite precipitation Location

Date

Discharge m3/s

T °C

SEC lS/cm

pH

Alk mmol/L

Ca2+ mmol/L

Mg2+ mmol/L

SICal

pCO2(eq) ppm

pCO2(eq;SICal ppm

= 0)

Ponor

19.9.2014

3.3

12.8

/

8.22

4.25

1.96

0.22

0.89

1,200

>10,500

Ponor

13.11.2014

52.5

11.6

320

8.10

3.03

1.48

0.15

0.51

1,200

>4,100

Ponor

4.6.2015

1.2

22.6

341

8.38

3.63

1.60

0.20

1.03

800

>10,200

Šumeča jama

2.9.2015

1.4

16.4

362

8.26

3.63

1.58

0.23

0.83

1,000

>7,600

Ponor

26.2.2016

23.3

7.4

340

8.22

3.37

1.58

0.16

0.63

900

>4,400

Ponor

16.2.2017

7.1

5.6

369

8.44

3.78

1.72

0.21

0.89

600

15,500

Ponor

16.9.2017

71.3

13.3

266

7.82

2.52

1.17

0.16

0.10

1,900

2,500

Ponor

11.12.2017

189.5

7.6

185

7.91

1.68

0.80

0.13

−0.21

1,000

/

Ponor

25.4.2018

4.4

13.4

344

8.48

3.55

1.61

0.16

0.99

500

>6,500

Ponor

4.12.2018

6.0

7.7

382

8.28

3.91

1.72

0.24

0.79

900

>6,300

Ponor

10.1.2019

1.9

1.4

384

8.39

3.88

1.76

0.20

0.80

600

>4,700

Ponor

3.2.2019

295.0

5.9

151

8.00

1.23

0.56

0.26

−0.43

500

/

During measurements with limestone tablets, 14 samples of water from the Reka River at the ponor to Škocjanske jame were taken and analyzed regarding temperature (T), specific electrical conductivity (SEC), pH, alkalinity (Alk), Ca2+ and Mg2+ concentration. Data were further processed using the Phreeqc software (Parkhust and Appelo 2014) that allows calculation of the calcite saturation index (SICal) and equilibrium aquatic CO2 partial pressure (pCO2), as well as inverse hydrochemical calculation―theoretical CO2 partial pressure before CO2 outgassing (at SICal = 0; pCO2 (eq; SICal = 0)) if water was oversaturated with respect to calcite (SICal > 0; Table 5.3). The electrical balance (on average +2%) between the analyzed anions (HCO3−, CO32−) and cations (Ca2+, Mg2+) as well as low concentration of occasionally measured SO42− (0.07 mmol/L or 6.7 mg/L) and Cl− (0.03 mmol/L or 3.1 mg/L) indicate a relatively pure Ca−Mg–HCO3 type of water. The concentration of cations clearly show dissolution of mainly calcite/limestone (Ca + Mg hardness of 0.82 −2.18 mmol/L; average Ca/Mg ratio of 8.2) already before the Reka River enters Škocjanske jame. Relatively high pCO2 (eq; SICal=0) (2,512–15,488 ppm) shows the reason for high rock dissolution already before entering Škocjanske jame, this is water flowing through a CO2 rich environment, most probably soil and karst aquifers. The latter is consistent with relatively high pCO2 (6,310−12,882 ppm) of nearly saturated water (−0.07 < SICal < 0.37) from two of the biggest upstream springs that feed the Reka River, which cannot be further sustained in the superficial stream leading to downstream CO2

outgassing and an increase in SICal. Substantially lower pCO2 (eq; SICal=0) is characteristic only for very high discharge (>71 m3/s) when SICal can be negative, indicating weaker interaction with soil with prevailing Horton overland flow as well as a smaller share of water from karst springs. The positive and significant linear correlation between Ca2+ + Mg2+ hardness, which shows an interaction with bedrock, and SICal (R2 = 0.89, p < 0.00001) supports this conclusion. The SICal of the Reka River at the ponor to Škocjanske jame, as the most relevant chemical factor controlling limestone dissolution and calcite precipitation rates, varies between +1.03 and −0.43; this suggests limestone dissolution when SICal < 0 as well as calcite precipitation when SICal >> 0 (usually even above 1; Dreybrodt 1988). Slow dissolution and precipitation rates are indicated by SICal values slightly below 0 and slightly below 1, respectively. SICal variation is exponentially correlated with discharge (Fig. 5.6a; N = 13), where the lowest SICal is observed during the highest discharge. Since positive SICal is characteristic of low, medium and high discharge, theoretical limestone dissolution is limited to periods of QReka 3 River > 109 m /s. Since such discharge occurs during severe floods 1.6 times per year (Fig. 5.4) and lasts several hours per year only, limestone dissolution along the underground Reka River in Škocjanske jame is a relatively rare as well as short process (Fig. 5.6b). This is in agreement with the low dissolution rates as measured by limestone tablets reached by discharge over 109 m3/s at Swidovo razgledišče (measurement site S-5) and Martelovo jezero (measurement sites

124

(a)

M. Blatnik et al.

(b)

Fig. 5.6 a Relation between discharge and SICal of the Reka River at Škocjanske jame and b calculated Reka River SICal at Škocjanske jame using the discharge and correlation from plot A

S-8 and S-9). Positive SICal during the 2nd and 3rd measurement periods (Fig. 5.6b) corresponds to prevailing calcite precipitation, as measured with limestone tablets at S-1 and S-2 (Table 5.2). The calculation of the theoretical threshold for calcite precipitation is highly limited since the SICal value when calcite precipitation starts can be highly site-specific due to interfering contaminants, like phosphates (Michaelis et al. 1984 after Dreybrodt 1988). However, since the concentration of contaminants in the Reka River like Cl− and SO42−, is recognized to be low, as well as that of concentration of o-phosphates (0.01 mg/L), calcite precipitation should be expected at relatively low positive SICal values (>  0.5). To measure calcite precipitation, downstream changes of Ca2+ and SEC were performed two times (2 September 2015 and 10 January 2019) along the underground Reka River in Škocjanske jame. However, even during very low discharge (Q < 1.9 m3/s) at SICal = 0.8 (at the Ponor), changes of both parameters were absent or negligibly low without trend. The lack of downstream SEC change, together with oversaturation and absent but expected changes of Alk due to CO2 outgassing, indicates tributaries along the underground Reka River with Alk and Ca2+ concentrations higher than found in the Reka River―a characteristic of percolation water. This makes downstream calculation of the calcite precipitation rate with observation of SEC inapplicable. Research of morphology partly overcame (as summarized in the following subchapter) this issue.

5.2.3 Comparison of Cave Micromorphology with Rates Measured by Limestone Tablets In Škocjanske jame, the underground stream passage is characterized by a spatially variable pattern of surfaces affected by abrasion (polished surfaces, potholes), attrition (mechanically rounded surfaces), calcite precipitation along the underground river (flowstone coating) and precipitation at drip sites (dripstones, rimstone dams), dissolution (scallops), breakdown (accumulation of collapse material, mainly in chambers), and sedimentation of fluvial sediments (slackwater deposits). An active micromorphology that can be expected as a result of processes measured with limestone tablets (flowstone coating and dissolutional features) can thus be observed in the underground stream bed. As expected from the low dissolution rates, dissolutional features formed by the underground river are absent several metres above the medium water level, probably due to the prevailing action of mechanical weathering. A several mm-thick flowstone coating is especially visible in the final part of the Škocjanske jame (downstream of Swidovo razgledišče). At Swidovo razgledišče, flowstone coating is abundant at the level of the lowest measurement sites (S-1, S-2, and S-3), indicating the prevailing role of calcite precipitation despite the lack of data during Q > 60 m3/s. At higher measurement sites (S-4 and S-5) a flowstone coating is absent, which is in general agreement with the measurements made with limestone tablets

5

Measurements of Present-Day Limestone Dissolution …

125

Fig. 5.7 Martelovo jezero during very low water level at Q  1 m3/s. The light brown coloured wall about 1 m above water level is flowstone cover precipitated from the Reka River during Q < 5 m3/s (photo courtesy of Borut Lozej, PŠJ)

indicating very low calcite precipitation or dissolution rates (Fig. 5.3a). Martelovo jezero is a prime example of the vertical transition from flowstone-coated to bare limestone wall, as detected by measurements (Fig. 5.3b) or morphological observation (Fig. 5.7). A comparison between the discharge-level curve, where the discharge taken into account has been measured at the Slovenian Environment Agency Reka River monitoring station Cerkvenikov mlin (0.5 km of flysch-limestone contact at the Reka River), and the water level in Martelovo jezero measured by Gabrovšek (unpublished), shows that the upper limit of flowstone coating (214.87 m a.s.l.; Figure 5.4) corresponds to a Reka River discharge of 5 m3/s. During such discharge, the calculated SICal equals 0.88 (Fig. 5.6a), which indicates apparent calcite precipitation above this threshold. Measurement site S-6 (214.94 m a.s.l.), where on average +2.2 µm/a of calcite precipitation can be expected according to measurements with limestone tablets, is located 7 cm higher than the upper limit or apparent flowstone coating. While this represents slight disagreement, the absence of flowstone coating at the altitude of measurement site S-7 corresponds to the slight dominant role of dissolution (−0.1 µm/a), as measured with limestone tablets at this level (Fig. 5.3b). In Škocjanske jame, dissolutional features, like scallops, are rare along the hydrologically active underground channel, which is in general agreement with massive sediment flux as well as low dissolution rates, where extensive time is needed for their formation. Wall notches that would show dissolution

during low-medium discharge are completely absent at the up to 80 m high vertical wall of the underground gorge, which is in accordance with the measurements made with limestone tablets. In addition, scallops are almost missing at the cave wall, confirming the low dissolution rates before backflooding. However, on average 9.6 mm wide and 36.8 mm long (Mihevc 2001), i.e. strongly elongated, scallops with sharp edges have been formed at massive, several m3 large stable boulders of limestone that have collapsed into the main underground channel. The horizontal position, as well as shape and size of the scalloped pattern (Slabe 1995, 23), depend on the shape of the limestone boulder and its relation to the main course of pebble transport and microlocal hydraulic characteristics. According to their vertical position (cca. 1– 2 m above the channel bed), they are exposed to several tens of m3/s of water flow, which is probably at the limit of net calcite precipitation but still in supersaturated conditions (up to SICal = + 0.4; Fig. 5.6a). The upper discharge limit for scallop formation is calculated to be at 105–120 m3/s when backflooding with an abrupt decrease in flow velocity occurs. Taking into account that water is undersaturated with respect to calcite above 109 m3/s, a short discharge window exists for solely dissolutional genesis of scallops; strong elongation of scallops suggests that during scallop formation dissolution could be overridden by abrasion caused by abundant siliciclastic suspended load (Ford and Williams 2007, 259). However, an idea that scallops might be formed also by erosion is not new since scallops have been found also at granites and orthogneiss (Bögli 1984).

126

5.3

M. Blatnik et al.

Conclusion

The results gathered by limestone tablets were compared with those from Reka River carbonate hydrochemistry and Škocjanske jame micromorphology. All three methodological approaches have their own advantages and drawbacks, and thus a combination of all enables crosschecking and more reliable conclusions. While the hydrochemical method with SICal indicates the momentary chemical process during sampling, the weight change of limestone tablets and micromorphology show a cumulative net process that is a balance between dissolution and calcite precipitation. Since the results of measurement with limestone tablets generally correspond to hydrochemical data and micromorphology, limestone tablets seem to represent a reliable cumulative methodology for determination of small dissolution rates ( 0.88, which is characteristic for the Reka River discharge below 5 m3/s. Between 5 and 109 m3/s, calcite precipitation from the Reka River seems to be in the range of tenths of µm, and as such out of the range of methodological accuracy. Due to short periods with Q > 109 m3/s, annual dissolution rates are also close to or below the accuracy of measurement with limestone tablets. Calcite precipitation with rates up to several µm/a is within the range of methodological accuracy. Despite the fact that measurements with limestone tablets indicate rates for period of slightly over a decade, while those for micromorphology are the result of processes 2–3 orders of magnitude longer, the micromorphology found in the underground channel is in general agreement with the presence of oversaturated water during low discharge (flowstone coating) and a weak dissolution rate during very high discharge (rare dissolutional features). In Škocjanske jame, MEM measurements (Mihevc 2001) show that by far the strongest erosional process is attrition followed by abrasion and dissolution, resulting in vertical entrenchment of the underground channel. Elongated scallops in the middle of the underground channel suggest the prevailing role of abrasion during scallop formation, but this hint needs further research.

References Bögli A (1984) Fließfazetten—ein kartshydrographish wichtiges Merkzeichen des Fließverhaltens von Kartswasser. Die Höhle 35 (3–4):119–126 Covington MD, Vaughn KA (2018) Carbon dioxide and dissolution rate dynamics within a karst underflow-overflow system, Savoy Experimental Watershed, Arkansas, USA. Chem Geol. https://doi. org/10.1016/j.chemgeo.2018.03.009 Dreybrodt W (1988) Processes in karst systems. Physics, Chemistry, and Geology. Springer, Berlin, Heidelberg, New York, London, Paris, Tokyo, p 288 Ford DC, Williams PW (2007) Karst hydrogeology and geomorphology. Wiley, Chichester, p 562 Gabrovšek F, Peric B (2006) Monitoring the flood pulses in the epiphreatic zone of karst aquifers: The case of Reka river system, Karst plateau, SW Slovenia. Acta Carsolog 35(1):35–45 Gams I (1959) Poskus s ploščicami v Podpeški jami (summary: A trial to measure with limestone tablets in Podpeška jama). Naše jame 1– 2:76–77 Gams I (1985) Mednarodne primerjalne meritve površinske korozije s pomočjo standardnih apneniških tablet/International comparative measurements of surface solution by means of standard limestone tablets. Razprave IV. reda SAZU 26, Ljubljana, 361–386 Gams I (1986) Nekatere metode ugotavljanja jamskih procesov/Some research methods dedicated to speleogenetic processes. Naše jame 28:32–38 Goudie AS, Sanderson M, Burt T, Lewin J, Richards K, Whalley B, Worsley P (1981) Geomorphological Techniques. George Allen and Unwin, London, p 395 Jennings JN (1982) The problem of cavern formation. In: Sharma HS (ed) Perspectives in Geomorphology. Recent trends, vol 1. Concept Publishing Company, New Delhi, pp 223–253 Kranjc A (1986) Transport rečnih sedimentov skozi kraško podzemlje/ Underground fluvial sediments transport as an example from Škocjanske jame (Kras, Slovenia). Acta Carsolog 14–15:109–116 Mihevc A (2001) Speleogeneza Divaškega krasa/The Speleogenesis of the Divača Karst. Zbirka ZRC 27, Ljubljana, p 180 (in Slovene language) Mikes T, Dunkl I, Frisch W, von Eynatten H (2006) Geochemistry of Eocene flysch sandstones of the NW External Dinarides. Acta Geol Hung 49:103–124 Newson MD (1971) The role of abrasion in cavern development. Trans Cave Res Group of Great Britain 13(2):101–107 Parkhurst DL, Appelo CAJ (2014). Description of input and examples for PHREEQC Version 3–A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations (book 6, section A, chapter 43). U.S. Geological Survey Techniques and Methods 2013 Prelovšek M (2012) The dynamics of the present-day speleogenetic processes in the stream caves of Slovenia. Založba ZRC/ZRC Publishing, Postojna-Ljubljana, p 152 Rebek R (1964) Poskus merjenja korozije/A trial to measure dissolution. Naše jame 6:38–40 Slabe T (1995) Cave Rocky Relief and its speleogenetical significance. ZRC 10, Ljubljana, p 128 Spate AP, Jennings JN, Smith DI, Greenaway MA (1985) The micro-meter: use and limitations. Earth Surf Proc Land 10(5):427–440 Zupan Hajna N, Mihevc A, Pruner P, Bosák P (2008) Palaeomagnetism and Magnetostratigraphy of Karst Sediments in Slovenia. Carsologica 8, Založba ZRC, Ljubljana, p 266

6

Water Quality Monitoring in Karst Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna

Around 13% of the Earth’s surface is covered by carbonate rocks, on which a specific karst landscape with extensive underground water system develops. In Europe, these areas comprise between 20 and 30% of the landmass (COST 1995; Ford and Williams 2007; Chen et al. 2017). Karst aquifers hold significant amounts of groundwater, which represents an important source of drinking water (e.g. in Slovenia, Austria and Croatia they supply more than 50% of drinking water needs, and in France, Slovakia and Belgium this share is 30%). The importance of aquifers with karst porosity for water supply is growing, and they are also increasingly recognized as a unique natural habitat (Culver and Pipan 2013; Stevanović 2015). Karst aquifers are complex systems characterized by triple porosity; the primary porosity is represented by micropores of the matrix, secondary porosity by the fractures and fissures, and tertiary by solutionally enlarged channels and conduits (Bakalowicz 2005; Ford and Williams 2007). Consequently, karst aquifers are conceptualized by strong heterogeneity of the hydrogeological structure, which can lead to non-uniform recharge characteristics. As a result, irregular distributions of contaminants that might enter karst aquifers in the process of recharge (Worthington 2009) can be expected. The complexity of flows in the karst aquifer

M. Blatnik
F. Gabrovšek
M. Knez (&)
B. Kogovšek
J. Kogovšek
C. Mayaud
A. Mihevc
J. Mulec
M. Năpăruş-Aljančič
B. Otoničar
M. Petrič
T. Pipan
M. Prelovšek
N. Ravbar
T. Shaw
T. Slabe
S. Šebela
N. Zupan Hajna Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia e-mail: [email protected] D. C. Culver American University, Washington, DC, USA H. Liu Yunnan University, Kunming, China

thus necessitates in-depth knowledge about the characteristics of water flow and storage, as well as regular monitoring of water availability and quality, in order to ensure adequate protection of karst water sources.

6.1

Characteristics of the Solute Transport Processes in a Karst Vadose Zone

In particular, characteristics of the vadose (unsaturated) zone— the upper part of karst aquifers—have a significant impact on the processes of infiltration, storage and transport within karst aquifers (Williams 1983). Generally, storage and further concentration of infiltrated water can occur (Aquilina et al. 2006). Understanding the role and importance of the vadose zone in infiltration mechanisms is fundamental for adequate protection and management of the groundwater in karst. Although several studies of these characteristics have been carried out in recent decades (Emblanch et al. 2003; Perrin et al. 2003; Pronk et al. 2009; Kogovšek and Petrič 2014; Feher et al. 2016 among others), the processes influencing the transport in karst systems remain insufficiently understood. The knowledge of hydrological dynamics and storage capacities of these zones is poor mainly due to limited access and lack of direct observations. This gap will be addressed by the present chapter, in which we aim to present the results of several tracer tests carried out during different hydrological conditions and using various modes of tracer injection on the surface of karst aquifers. Effects of the vadose zone on groundwater storage and transport characteristics have been evaluated at local and regional scales, in which either cave drips or springs have been monitored. The findings have been compared with the aim to improve the understanding of the infiltration processes and to use the findings in the planning of the water quality monitoring in karst. Finally, detail guidelines for karst water quality monitoring have been prepared.

© Springer Nature Switzerland AG 2020 M. Knez et al. (eds.), Karstology in the Classical Karst, Advances in Karst Science, https://doi.org/10.1007/978-3-030-26827-5_6

127

128

6.1.1 The Influence of Hydrological Conditions, Injection Mode and Geologic Heterogeneities Only in a few studies the tracer injection at the land surface and sampling drips inside the cave have been applied to define the characteristics of flow and transport of substances in the vadose zone (Bottrell and Atkinson 1992; Čenčur Curk et al. 2001; Perrin et al. 2004; Goldscheider et al. 2008; Flynn and Sinreich 2010). Here the results of three long-term tracer tests carried out in the system of Postojnska jama in Slovenia (Kogovšek and Šebela 2004; Kogovšek and Petrič 2014) are compared. The tests were carried out on the same study area but during different hydrological conditions. Various tracer injection modes were applied on the surface above the cave gallery of Kristalni Rov with *100 m of overlying Cretaceous limestone (for location see Fig. 6.1). The tracer breakthrough curves were monitored in a cave gallery at three drips of different hydrological types (labelled I, J, and L) over several years. According to the method proposed by Baker et al. (1997) the drip I can be classified as ‘‘subcutaneous flow’’, and the drips J and L as “seasonal drips’’. According to the structural mapping, the fastest percolation (drip I) occurs in fissured to moderately fractured zones, while slower percolation flows along tectonically fractured zones (drip J) and bedding planes (drip L) (Kogovšek and Šebela 2004). The main aim of the study was to assess the influence of hydrological conditions, injection mode and heterogeneous structure of the vadose zone on the solute transport. The method, study area and results are described in more detail in Kogovšek and Šebela (2004) and Kogovšek and Petrič (2014), here only the main characteristics and findings are summarized. On 7 June 1993 (1st tracer test), a solution of 60 g of uranine was injected and flushed with 6 m3 of water at the bottom of the 4 m deep cesspool (dug into a solid limestone), in which the wastewater from a small facility was drained in the past. The vadose zone was relatively dry and the rapid and simultaneous appearance of water and uranine in the previously dry drip I was caused by artificial flushing of the tracer with a large amount of water. The concentration was very high (the maximum of 22,000 mg/m3 only 75 min after it was flushed with water) as there was no homogenization of the tracer with the flushed water. In one day the drip ran dry and in this period just under 4% of the injected water carrying 2.2% of the injected uranine flowed through drip I (Table 6.1). These results indicate that in dry conditions, artificial flushing of the injected tracer with a large amount of water has a limited impact. Only the most permeable fissures are capable of draining some water and substances dissolved in it and a rapid flow with no major

M. Blatnik et al.

dilution can be expected. On the other hand, a significant part of the injected water and tracer was stored in poorly saturated parts of the vadose zone, and only after abundant precipitation three months after injection were the fissures and pores in the vadose zone filled with water and hydraulically connected so that the transit of tracer to all three drips was observed. This is reflected in significant difference of linear dominant velocities of percolation between drip I (80 m/h) and drips J (0.045 m/h) and L (0.044 m/h). In drips J and L the concentration dropped below the detection limit (0.005 mg/m3) after two years, and in drip I after three years. On 17 November 1996 (2nd tracer test), a solution of 15 g of uranine was injected at the same point as in the 1st test and no artificial flushing was applied. Before the injection, many pores within the vadose zone were filled with water due to previous precipitation and the immediate transit of tracer to the three drips observed was possible. The difference in the linear dominant velocity of percolation to the different drips (4.3 m/h for drip I, 0.7 m/h for drip J, and 1.0 m/h for drip L) was smaller than in the 1st tracer test. During such wet periods with significant amount of water previously stored in the vadose zone, precipitation infiltrates immediately and continuously, the entire catchment area of drips including the network of least permeable fissures becomes filled with water, and the simultaneous pushing of water and the solute transport through the vadose zone results. There is an immediate, continuous, and relatively homogenous transit of substances along all the available fissures and conduits with considerable dilution. During the first month after the injection only 0.2% of the injected uranine flowed through drip I, and even less through drips J and L. Further flushing of the tracer followed after every precipitation event and lasted for 20 months in drip I, four months in drip J, and two months in drip L when the concentrations fell below the detection limit. On 7 June 2002 (3rd tracer test), a solution of 60 g of eosin was injected on the surface near the cesspool, directly on the approximately half a metre of deposited sediment (mixture of rock fragments and soil formed during excavation) with 10 cm thick layer of soil with grass and flushed only naturally by subsequent precipitation. Hydrological conditions were similar as during the 1st tracer test with only some minor precipitation in the following summer months. The first occasional and short-term appearances of eosin after two months were the consequence of being pushed by the preferential flow only along the most permeable paths through the dry soil. However, a continuous transit of eosin through drips J and I started only after further infiltration of precipitation several months after the injection with the start of more intensive outflow of eosin from all observed drips in November 2003 (17 months after the injection), when after

6

Water Quality Monitoring in Karst

129

Fig. 6.1 Hydrogeological map of the studied area with underground water connections identified by the tracer tests. The points of the greatest focus of this chapter are marked in red

Table 6.1 Linear dominant flow velocities (vdom) and recovery rates for flow through variously permeable parts of the vadose zone. Periods of the recovery assessment have various durations depending on the characteristics of the tracer breakthrough curves

Vadose zone (surface—drips in caves) Injection mode

Well permeable zones

Less permeable zones

vdom (m/h)

R (%)

vdom (m/h)

R (%)

(a) On bare rock, flushed with water, dry conditions, *100 m thick vadose zone

80

2.2 (1 day)

0.045

0 (1 day) 0 (3 months)

(b) On bare rock, not flushed with water, wet conditions, *100 m thick vadose zone

4.3

0.2 (1 month)

0.7

0.005 (1 month)

(c) Over *0.5 m thick overlying layer, not flushed with water, dry conditions, *100 m thick vadose zone

0.003

< 0.001 (1 month) 0.05 (1 year)

0.003

< 0.001 (1 month) 0.025 (1 year)

130

abundant rain the fissures and pores in the soil and karst rock vadose zone were hydraulically connected. An increasing trend of concentrations was observed until the fall of 2005 (40 months after the injection) when the maximum concentrations were detected (2.5 mg/m3 in drip I and 5.5 mg/m3 in drip J) and linear dominant flow velocities 0.003 m/h to drips I and J were calculated. In the following years the concentrations gradually decreased, in 2013 (136 months after the injection) in drip I the concentration was near detection limit (0.06 mg/m3) but higher in drip J (100 m above the base flow level (Fig. 8.12).

(a)

(b)

Fig. 8.12 a Cross-section through Škocjan Caves and Kačna Cave with the position of observation points P1 and P2. Dark blue lines/regions indicate low flow water positions, and the pale blue

(c)

shows the floodwater situation; b detailed view of the region of P2 in Kačna Cave; c flow routing at low flow (solid line) and high flow (dotted line) behind P2

158

8.3.1.3 Flood Response Figure 8.13 shows the response of the water level in Škocjan Caves (P1) and Kačna Cave (P2) during three events with different peak flows. During a small event, comparable responses at both locations are recorded (Qmax = 23 m3/s, Fig. 8.13a). In a medium event (Qmax = 85 m3/s, Fig. 8.13 b), the level at P1 rises to 4 m, while the level at P2 shows a steep rise to 15 m and slow recession (–2 m/day), as long as the flow rate is above 15 m3/s. Finally, it recedes at the rate of about –4 m/day to the base level. During a large event (Qmax = 250 m3/s, Fig. 8.13c) stage rises vigorously to 65 m at P1 and 73 m at P2, where it drops rapidly almost to the base level when the discharge drops below 100 m3/s, while at P2 stays elevated until Q > 15 m3/s. During the rising stage of the medium and large events, inflection at about 13 m can be observed at P2, suggesting an overflow level.

M. Blatnik et al.

The situation is clearer in Fig. 8.14, which shows the level at P1 and P2 as a function of the Reka River flow rate for the entire observation period. For Q < 100 m3/s, P1 stays below 4 m, while the level at P2 rises above 10 m for Q > 20 m3/s. When flow is higher than 130 m3/s, a steep rise with similar characteristics at both locations is observed. The interpretation of the response and stage-discharge curves is given in Gabrovšek et al. (2018) and is based on the known geometry and base flow directions in Kačna Cave (see Fig. 8.12). There, the flow at low stage enters a narrow channel, which ends in a sump at 156 m a.s.l. The limited capacity of this outflow back-floods this part of the cave and diverts water into large galleries positioned about 9 m above the instrument. This obvious overflow resolves the first inflection in Kačna Cave (Fig. 8.13b, c).

(a)

(b)

(c)

Fig. 8.13 Stage and temperature hydrographs at Škocjan Caves (P1) and Kačna Cave (P2) during a small, b medium and c large flood events. Note that the range of stage axis differs between the cases

8

Deciphering Epiphreatic Conduit Geometry from Head and Flow Data

(a)

159

(b)

Fig. 8.14 Stage at P1 and P2 as a function of Reka River flow rate. a entire cloud of data points for Q < 100 m3/s; b situation at a large flood event of December 2008. Note the common inflection towards steep rise at about 130 m3/s, marked by grey arrows

However, a more interesting question is what causes large floods in Kačna Cave and particularly in Škocjan Caves, where the major inflection in the stage-discharge curve occurs at about 130 m3/s (Fig. 8.14b). This inflection is always slightly preceded by a major inflection in Kačna Cave (grey arrows in Fig. 8.14b), which suggests that the back-flooding is triggered by the constriction behind the observation point in Kačna Cave.

(a)

Another insight is given by Fig. 8.15, which shows the relation between heads at both points. Two major floods from December 2008 and February 2009 deviate as large loops. During the rising stages of both flood events, the heads at both caves start to correlate, when the head in Kačna Cave rises above 190 m a.s.l. Only a small deviation between both floods occurs during further increase (Fig. 8.15b). In general,

(b)

Fig. 8.15 a Black curve: the relation between heads in Škocjan Caves (P1) and head in Kačna Cave (P2). The grey curve shows difference HŠkocjan–HKačna. b rising stage of the curve in the region marked by a rectangle in Fig. 8.16a

160

the loops in such correlation plots are caused by time delay between response at the points and/or by the stored water between both points, which becomes the sole reason when both points are fully hydraulically connected. In this case, the additional flow of the stored water results in slower recession at the downstream point, as compared to the upstream point. Larger floods may store more water between the points, which makes their hysteresis larger, as can be seen in Fig. 8.15a. Note that the rate of head rise at P1 becomes higher compared to the rate at P2, when it is reached by back-flooding. The reason for this is that there are several conduits between both points that become pressurized when back-flooded, resulting in a large head-drop along them.

8.3.1.4 SWMM Model of the Hydraulic Response to High Recharge Event We have modelled flood propagation through Škocjan Cave and Kačna Cave with SWMM. The model is based on the one presented by Gabrovšek et al. (2018), but only the first part of the system, relevant for P1 and P2, is taken and optimized manually. The plan view of the model is shown in Fig. 8.16a and the cross-section at different flood stages in Fig. 8.16c. Figure 8.16b shows observed and measured response at P1 and P2 during the period of the February 2009 flood. Despite the fact that the model’s geometry is highly simplified and partially unknown, the model captures all characteristics of the observations. Four stages of the flood event are shown in Fig. 8.16c(1–4): • before the flood, when all the water is drained by the low water sump beyond P2 (Fig. 8.16c1); • when overflow is active and P2 is already back-flooded, but the response at P1 is still small (Fig. 8.16c2); • at the peak, where all conduits are pressurized (Fig. 8.16c3); and • when P1 has dropped almost to base level and P2 is still high (Fig. 8.16c4).

8.3.1.5 Flood Event in February 2019 Between 27 January and 4 February 2019, over 300 mm (almost 200 mm in the most intensive 30 h period) of rain fell in the mountainous region of Mt. Snežnik and about 150 mm in the area of Škocjan. The discharge of the Reka River at the Cerkvenikov Mlin gaging station peaked at 300 m3/s. During the event the water in Škocjan Caves rose at rates up to 10 m/h and reached a level of 305 m a.s.l. in Martel’s Chamber (Figs. 8.17 and 8.18) and about 307.5 m a.s.l. in Šumeča Jama. The flood was the largest in the last 50 years. High water caused severe damage to infrastructure and deposited a considerable amount of mud; at some places the thickness of fresh deposits was above 50 cm (Fig. 8.19).

M. Blatnik et al.

8.3.2 Ljubljanica River Recharge Area The Ljubljanica River Recharge area is an over 1600 km2 large karstic catchment in central Slovenia. The regional groundwater flow is governed by complex structures comprising thrusts and large fault zones. The most dominant of the latter is the Idrija Fault Zone (IFZ), which crosses the area in a SE–NW direction and acts as a barrier for groundwater flowing from the mountainous regions of the South, towards the Ljubljana Basin at the north. Along the Idrija Fault Zone a cascading set of karst poljes with overland flow has formed. Poljes exchange water with the surrounding karst massifs via springs, ponors and estavelas. We present a selection of results based on observations in caves and ponors between Planinsko Polje, and the springs of the Ljubljanica River near Vrhnika, at the rim of the Ljubljana Basin (Fig. 8.20). Planinsko Polje is the NW-most of the active poljes formed along the Idrija Fault Zone. It is an overflow polje with main springs on its southern side, gathering waters from higher positioned poljes and mountainous areas to the south. The springs merge into the Unica River (Qmin = 1.1 m3/s, Qav = 21 m3/s, Qmax > 100 m3/s) with almost 17 km of flow length along the 5 km long polje. After about 5 km of flow the river approaches the border of the polje and loses most of its low to medium flow along the Eastern Ponor Zone (Blatnik et al. 2017). During floods, the limiting capacity and/or back-flooding of the Eastern Ponor Zone diverts the excess of flow towards the ponor zone at the northern border of the Polje. When the recharge exceeds about 60 m3/s, the Polje starts to flood. During the highest floods, up to 100  106 m3 of water can be stored in the Polje. The results presented in this chapter are based on three years of observations in ponors P1–P3 and caves E1, E2, W1– W3, H1 and H2 (Fig. 8.20). Detailed results and descriptions of the methods are given in Blatnik et al. (2019). The flow system adjacent to Planinsko Polje is extremely complex and intertwined; however, Blatnik et al. (2019) have shown that the main characteristics of groundwater dynamics can be explained with the basic principles given above and simulated with relatively simple SWMM models. Here we present some examples. Based on the past research, the area can be divided into the three subsystems, which are shown in Fig. 8.20: • the system related to the Eastern Ponor Zone (P1–E1–E2), • the system linked to the Northern Ponor Zone (P2, P3– W1–W2–W3), and • the system related to flow from the Hrušica Plateau (P2*, H1, H2).

8

Deciphering Epiphreatic Conduit Geometry from Head and Flow Data

Fig. 8.16 a Plan view of the SWMM model; b modelled (dashed lines) and observed (full lines) responses at P1 and P2 during the flood event in February 2009. The recharge is shown by grey dotted line. Points 1–4 show four positions of stages presented in Fig. 8.16c; c cross-section of the model at four stages during flood event (see the text in the Sect. 8.1.3.4. Pale blue regions denote the water level, green lines show total had along the profile

(a)

(c)

161

(b)

162

M. Blatnik et al.

Fig. 8.17 The flood event of 2019: cumulative rain at two stations, discharge of the Reka River and level and temperature in Martel’s Chamber. Dotted grey line shows discharge shifted for six hours, an estimated travel time from gaging station to Martel’s Chamber

Fig. 8.18 A simplified extended elevation of Škocjan Caves with approximate maximal water level during the flood of February 2019

Figure 8.21 shows levels at P1, E1 and E2 in February 2017. The observation point E1 is in a shaft connecting the base flow conduits to an overflow channel. The observation point at E2 is close to the inflow sump. The connection between E1 and E2 is not explored, but the data indicate very good hydraulic connectivity between the points (Fig. 8.21). Note that the level drop between the Polje (P1) and E1 is much smaller than between E1 and E2, indicating that the back-flooding of the ponors is caused by the limiting transmissivity of the conduit system, deeper in the aquifer.

At E1, the most evident inflection point corresponds to the position of a major overflow channel at 440 m a.s.l. Correlation of heads at E1 and E2 shows similar hysteresis at all major flood events (Fig. 8.22). During the rising stage, the head at E1 initially rises rapidly until the overflow passage at 440 m a.s.l. is reached. The head at E1 is then bound to the position of the overflow, while rapid increase continues at E2 due to active overflow. Further head increase at both points is controlled by restriction beyond E2, where both points and the overflow are back-flooded. The recession at both points

8

Deciphering Epiphreatic Conduit Geometry from Head and Flow Data

163

Fig. 8.19 Photos of the 2019 flood: a Velika Dolina collapse valley; b, c Šumeča Jama (Rumouring Cave); d flood deposits on the footpath in Hanke’s Channel

initially follows the rise, but then deviates from the rising curve. Blatnik et al. (2019) proposed a model, which includes relatively large storage in the overflow passage (Fig. 8.23). During the recession, the inflow of the stored water prevents head-drop at E2. The concept was tested by a SWMM model, which produced hysteresis in the correlation plot if the overflow conduit between E1 and E2 had considerable storage (Fig. 8.22b). Similar principles, tested by SWMM models, were used by Blatnik et al. (2019) to analyse hydrographs from the other two subsystems delineated in Fig. 8.20. In the subsystem related to the northern ponors (P2, P3, W1–W3), the flow from ponor zone P2 bypasses the nearest cave W1 and feeds directly the region of W2–W3. When the ponor zone P2 is back-flooded, the flow in the polje is re-routed to higher positioned channels leading to P3, which then triggers fast response at W1. The concept is shown in Fig. 8.24.

They also identified several overflow levels between W1– W2–W3. Some of these were expected from the cave surveys, some were unexpected (Fig. 8.25). Blatnik et al. (2019) also introduced a plot, where rate of water rise/drop is plotted against the head. As expected, the rate show minima at the positions of overflow conduits (Fig. 8.26). System H1–H2 receives autogenic recharge from the region of the Hrušica Plateau to the south and from the mixed recharge of the Hotenjka region to the west. H1 and H2 are on the opposite (SW) side of Idrija Fault Zone with respect to other observation points (E1–E2, W1–W3). H1 is a simple shaft, reaching a very stagnant water level and H2 is a shaft, which becomes partially flooded during high water events. During high water events (Blatnik et al. 2019), the level in the region of H1 and H2 increases rapidly and the region discharges to the NW side of Planinsko Polje. The level at H1 and H2 also recedes fast and the water flows from

164

M. Blatnik et al.

Fig. 8.20 The area between Planinsko Polje and Ljubljanica Springs, showing all observation points: monitored ponors (triangles) and water caves (squares). The dashed lines delineate flow systems; see text for discussion

the flooded polje into the region of H1–H2. The hydrographs at H1 also indicate a high transmissivity level in the Idrija Fault Zone, which keeps a very stable water level at H2.

During floods, the area of H1–H2 seems to be back-flooded due to constrictions along the flow paths on the down-flow side of the Idrija Fault Zone.

8

Deciphering Epiphreatic Conduit Geometry from Head and Flow Data

165

Fig. 8.21 Levels (upper panel) and temperatures (lower panel) at P1, E1 and E2 and flow rates of the Unica River during winter 2016

(a)

(b)

Fig. 8.22 Correlation between heads at observation points in E1 and E2: a measurements during several high water events; b results of a modelled event, with hysteresis indicating storage between the two observation points

Fig. 8.23 SWMM model of the system P1, E1, and E2 at high water

166

M. Blatnik et al.

Fig. 8.24 Northern border of Planinsko Polje with ponor zones P1 and P2, Najdena Jama (W1) and inferred flow directions. The back-flooding of P2 diverts the flow on the polje towards P3, which is followed by a fast response at W1. From Blatnik et al. (2019)

(a)

(b)

date (day / month)

Fig. 8.25 a Level hydrographs at W1–W3 during a flood event in May 2016. Grey lines denote positions of overflow; b hydrographs obtained from SWMM model of conduit system between P2, P3 and W1–W3. From Blatnik et al. (2019)

8

Deciphering Epiphreatic Conduit Geometry from Head and Flow Data

Fig. 8.26 Rate of head increase/decrease at W2 shows a clear minimum at the overflow position at 400 m a.s.l. This corresponds to the inflection marked in Fig. 8.25a and to the position of the known existing channel

8.4

Conclusion

Several other studies in the Dinaric Karst demonstrated the power of combining observations in cave systems and hydraulic modelling to understand the function of a karst aquifer. Kaufmann et al. (2016) used the approach to analyze the observations at six stations positioned along the underground flow of the Pivka River in Postojna Cave. They employed a survey of the conduit system as an initial geometry, which was further constrained by an optimization procedure resulting in an excellent fit of the observed data. A recent ongoing study is examining the springs of Planinsko Polje. There, an interesting distribution of flow between the two main springs seems to be controlled by an overflow over a breakdown zone in the region of Planinska Jama, where two main inflows merge into a lake and then diverge towards base flow and overflow springs. Kaufmann et al. (2019) tested this hypothesis using the known geometry of the conduit system and SWMM model, optimized to

167

fit the archival data of flow rates of springs and contributing ponors. Ongoing research also includes observations within the system and will provide more details on the mechanisms involved. In this chapter most of the discussion was focused to the level hydrographs, although temperature, specific electric conductivity and/or other observed parameters may give us further insights into the system, such as travel time estimation between points, onset and cessation of overflow mechanism, etc. Examples from the Dinaric karst are given in Gabrovšek et al. (2018), Covington et al. (2011), and Blatnik et al. (2019). Due to remoteness and difficult accessibility, caves have been rather overlooked as observation points within karst aquifers. However, as shown by recent studies, observation of epiphreatic flow at multiple access points combined with hydraulic modelling offers new insights into the structure and mechanism of hydraulic processes in the karst conduit systems. The importance of good cave surveys, which enable building of the initial models and give constraints to the final model applied, is paramount. Therefore, the volunteering and enthusiastic work of cavers is highly appreciated. It is also important to stress that models which give a good qualitative or quantitative fit to the observed data do not necessarily represent what is actually present in nature (i.e. unique solutions). However, they do provide a physically based explanation of what may be there or why the hydrographs have a given shape. Additional theoretical work is needed to obtain better data processing and automatic identification of features and mechanisms. Another interesting question is how much information about the phreatic zone is hidden in the data.

References Audra P, Palmer AN (2013) The vertical dimension of karst: controls of vertical cave pattern. In: Shroder JF (ed) Treatise on geomorphology 6. Academic Press, San Diego, California, pp 186–206 Blatnik M, Frantar P, Kosec D, Gabrovšek F (2017) Measurements of the outflow along the eastern border of Planinsko Polje, Slovenia. Acta Carsolog 47(1):83–93 Blatnik M, Gabrovšek F, Mayaud C (2019) Groundwater dynamics between Planinsko Polje and springs of the Ljubljanica River, Slovenia. Acta Carsolog 48(2):199–226 Chen Z, Goldscheider N (2014) Modeling spatially and temporally varied hydraulic behavior of a folded karst system with dominant conduit drainage at catchment scale, Hochifen-Gottesacker, Alps. J Hydrol 514:41–52 Chow VT (1988) Open-channel hydraulics. McGraw-Hill, New York Covington MD, Luhmann AJ, Gabrovšek F, Saar MO, Wicks CM (2011) Mechanisms of heat exchange between water and rock in karst conduits. Water Resour Res 47(10):W10514

168 Dingman SL (2002) Physical hydrology. Prentice Hall, Upper Saddle River, N.J. EPA U (2014) Storm water management model (SWMM). US Environmental Protection Agency. http://www.epa.gov/nrmrl/ wswrd/wq/models/swmm/ Ford DC, Williams PW (2007) Karst hydrogeology and geomorphology. Wiley, Chichester, p 562 Gabrovšek F, Peric B (2006) Monitoring the flood pulses in the epiphreatic zone of karst aquifers: the case of Reka river system, Karst plateau, SW Slovenia. Acta Carsolog 35(1):35–45 Gabrovšek F, Häuselmann P, Audra P (2014) ‘Looping caves’ versus ‘water table caves’: the role of base-level changes and recharge variations in cave development. Geomorphology 204:683–691 Gabrovšek F, Peric B, Kaufmann G (2018) Hydraulics of epiphreatic flow of a karst aquifer. J Hydrol 560:56–74 Jeannin P (2001) Modeling flow in phreatic and epiphreatic karst conduits in the Holloch cave (Muotatal, Switzerland). Water Resour Res 37(2):191–200

M. Blatnik et al. Kaufmann G, Gabrovšek F, Turk J (2016) Modelling cave flow hydraulics in Postojnska jama, Slovenia. Acta Carsolog 45(1): 57–70 Kaufmann G, Mayaud C, Kogovšek J, Gabrovšek F (2019) Understanding the temporal variation of flow direction in a complex karst system Planinska jama, Slovenia. Acta Carsolog (in press) Peterson E, Wicks C (2006) Assessing the importance of conduit geometry and physical parameters in karst systems using the storm water management model (SWMM). J Hydrol 329(1–2):294–305 Rossman LA (2009) Storm water management model, Version 5.0. US Environmental Protection Agency, Cincinnati Rozos E, Koutsoyiannis D (2006) A multicell karstic aquifer model with alternative flow equations. J Hydrol 325(1–4):340–355 Šebela S (2009) Structural geology of the Škocjan Caves (Slovenija). Acta Carsolog 38(2–3):165–177 Vuilleumier C (2019) Hydraulics and sedimentary processes in the karst aquifer of Milandre (Jura Mountains, Switzerland). University of Neuchatel, Neuchatel

9

Microbial Underground: Microorganisms and Their Habitats in Škocjanske Jame Matej Blatnik, David C. Culver, Franci Gabrovšek, Martin Knez, Blaž Kogovšek, Janja Kogovšek, Hong Liu, Cyril Mayaud, Andrej Mihevc, Janez Mulec, Magdalena Năpăruş-Aljančič, Bojan Otoničar, Metka Petrič, Tanja Pipan, Mitja Prelovšek, Nataša Ravbar, Trevor Shaw, Tadej Slabe, Stanka Šebela, and Nadja Zupan Hajna Caves represent a discontinuity in a rock matrix and are considered as “dark openings” into the underground. Typical cave features—voids, cracks, fissures, or conduits—are filled with air (or mixture of various gases), water, or solid inorganic and/or organic material. Cave habitats are almost never devoid of life and often host a very diverse biota, including microorganisms. These can move between different cave habitats and engage in interactions among themselves and with the environment, including the deep geosphere. One of the main drivers of microbial transport and dispersion is the cave air. In addition, microorganisms can be transported and dispersed by migratory cave animals—vectors, such as bats. Furthermore, cave microorganisms can bridge long distances by taking advantage of the water cycle, but in doing so they must be able to adapt to the environmental changes induced by the movement of water through the rock matrix, such as changes in salinity, temperature, and pH. Caves with sediments allow researchers to study past geological events (Ford and Williams 2007; Zupan Hajna et al. 2008), but are also important microbial habitats. In contrast to most cave habitats, cave sediments are often nutrient-rich, particularly when they contain animal excrements, such as bat guano. The organic matter in the bat guano supports the growth of microorganisms while serving as a source of microorganisms for colonization of other cave habitats. Some microorganisms can adapt to these harsh

M. Blatnik
F. Gabrovšek
M. Knez (&)
B. Kogovšek
J. Kogovšek
C. Mayaud
A. Mihevc
J. Mulec
M. NăpăruşAljančič
B. Otoničar
M. Petrič
T. Pipan
M. Prelovšek
N. Ravbar
T. Shaw
T. Slabe
S. Šebela
N. Zupan Hajna Research Centre of the Slovenian Academy of Sciences and Arts, Karst Research Institute, Postojna, Slovenia e-mail: [email protected] D. C. Culver American University, Washington, DC, USA H. Liu Yunnan University, Kunming, China

conditions by producing new organic matter in chemosynthetic reactions that form a basis for the underground ecosystem (Kumaresan et al. 2015; Sarbu et al. 1996). Other cave microbes take advantage of nutrient availability by forming complex structures, such as biofilms and mats. Furthermore, microbial driven lithogenesis—induction of mineral precipitation (Dupraz et al. 2009; Taboroši 2006) or litholysis—and dissolution of stony substrata (Lian et al. 2008) can also be observed at some cave sites. Being part of a global ecosystem, the underground is subjected to a certain level of anthropogenic impact. Human external interventions include pollution events, disruption of physical habitats, and opening the cave to the public as a tourist attraction. These interventions alter cave environmental conditions, influence the metabolic base of the cave ecosystem, and its evolutionary trajectory. The impact of humans on the health of the environment can be quantified using environmental parameters, such as microbial indicators. Certain microorganisms are indicators of environmental changes (e.g. climate; Singh et al. 2010). Microorganisms have evolved various strategies to survive even in such disturbances. Therefore, a single cave can be a highly diverse ecosystem (Fig. 9.1). Microbiology of the karst underground and its cave networks has long been understudied. With the development of “omics” (i.e. metagenomics, transcriptomic, and metabolomics), we now have the necessary tools to understand the microbial diversity, metabolic base of different cave settings, interactions, biogeochemical cycles, and dynamics in time and space (Jones 2015). While a metagenomics study of the cave microbiome of Škocjanske jame is currently in progress, its preliminary results indicate high levels of species and metabolic diversity. Here, we give a review of the current knowledge of microbial habitats and accompanying microbiota in this cave setting, which is also a UNESCO World Heritage Site. This cave system is highly impacted by external conditions with clearly visible interceptions of different habitats and associated microorganisms (Fig. 9.1).

© Springer Nature Switzerland AG 2020 M. Knez et al. (eds.), Karstology in the Classical Karst, Advances in Karst Science, https://doi.org/10.1007/978-3-030-26827-5_9

169

170

M. Blatnik et al.

Fig. 9.1 Representation of microbial habitats in Škocjan Caves. Legend 1 tufaceous stalactite, 2 stromatolitic stalagmite, 3 phototrophic mat, 4 lampenflora, 5 water seepage, 6 ponor of the Reka River, 7 sediment deposit, 8 bat guano, 9 tourist infrastructure and a footpath, 10 aerosols

9.1

A Short Overview of Škocjan Caves

Škocjanske jame (Škocjan Caves, 45°39′53.33″N 13°59′ 40.44″E) are located in the heart of Classical Karst of Slovenia. The caves were formed by the large sinking Reka River. The main, active part of the caves is spacious, with a