Chemostratigraphy of the Early Paleoproterozoic Carbonate Successions (Kaapvaal and Wyoming Cratons)
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CHEMOSTRATIGRAPHY OF THE EARLY PALEOPROTEROZOIC CARBONATE SUCCESSIONS (KAAPVAAL AND WYOMING CRATONS) by Andrey Bekker Dissertation submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Phylosophy in Geological Sciences Kenneth A. Eriksson (Chair) Richard K. Bambach Juha A. Karhu A. Jay Kaufman J. Fred Read J. Donald Rimstidt August, 24, 2001 Blacksburg, Virginia Keywords: Paleoproterozoic, chemostratigraphy, carbonates, climate change, glacials, biogeochemical cycling of carbon Copyright, 2001, Andrey Bekker CHEMOSTRATIGRAPHY OF THE EARLY PALEOPROTEROZOIC CARBONATE SUCCESSIONS (KAAPVAAL AND WYOMING CRATONS) by Andrey Bekker K. A. Eriksson, Chairman Department of Geological Sciences, Virginia Tech (ABSTRACT) Evidence of three glaciations in Paleoproterozoic successions of North America and at least one on three other continents, suggests that these glaciations were of global extent. In common with the Neoproterozoic record, carbonates cap the glacials. However, the relationship between biogeochemical cycling of carbon and ice ages has not been fully appreciated. This research involved the sedimentology and isotope stratigraphy of carbonates and shales in Paleoproterozoic glacially-influenced successions of Wyoming and South Africa. Carbonates of the Vagner Formation cap the middle of three diamictites in the Snowy Pass Supergroup, Medicine Bow Mountains, WY. The Duitschland Formation occurs between two glacial horizons in South Africa. Limestones retain negative δ13C values for over 60 m in the Vagner Formation, and for over 100 m in the lower part of the Duitschland Formation. Isotope compositions of TOC from the lower part of the Duitschland Formation reveal pronounced enrichment resulting in significantly lower fractionation between organic and inorganic carbon. This is similar to enrichment noted in Neoproterozoic cap carbonates. Combined with strongly positive carbon isotope compositions in upper Duitschland carbonates, the data from the Vagner Formation underscores strongly positive-to-negative carbon isotope trends bracketing Paleoproterozoic glaciations. These trends mimic those noted in Neoproterozoic glacial successions and possibly indicate a recurrence of global glaciations. The Slaughterhouse and Nash Fork formations significantly postdate the glacial epoch. Both the lower part of the Nash Fork Formation, Medicine Bow Mountains and the Slaughterhouse Formation, Sierra Madre contains carbonates with 13C-enrichment >+6‰ and locally up to +28‰, whereas carbonates higher in the Nash Fork Formation have δ13C values between 0 and 2.5‰. This dramatic change in the composition of the Paleoproterozoic ocean is constrained at ca. 2.1 Ga (Karhu, 1993). Carbonates in the Rawhide Canyon section of the Whalen Group in the Hartville Uplift (the easternmost exposure of the Wyoming Craton) display δ13C values up to +8.2‰ suggesting correlation with the Slaughterhouse and Nash Fork formations and their deposition on continuous carbonate platform along the margin of the Wyoming Craton. These data support an open-marine, and therefore a global origin for the ca. 2.2-2.1 Ga carbon isotope excursion. iii ACKNOWLEDGMENTS I would like to thank Dr. Kenneth A. Eriksson for serving as the chairman of my committee. His help in interpreting the data and editing my writing during the later stages of this project is most appreciated. This project would not have started without the advice, help and support provided by Dr. Juha A. Karhu, formerly with the Finnish Geological Survey and now with the Department of Geology, University of Helsinki. Dr. Karhu and his technical staff helped to analyze many samples for this project. Dr. A. Jay Kaufman’s work on the Neoproterozoic successions inspired my interest in the relationship between biogeochemical cycling of carbon and climatic changes. He provided lab facilities, a place to stay, and funding for analytical work in his lab. Discussions with Fred Read, Don Rimstidt and Richard Bambach helped to shape my understanding of Paleoproterozoic environmental changes. I also appreciate the support the rest of the faculty in the department offered me over the years. Thank you to the paleo- and structure people for their help and tolerance towards a stranger in their quarters. I offer thanks to the Department of Geological Sciences for their continuous support in the form of graduate teaching assistantships for the last five years, as well as for the fellowships to carry out analytical and fieldwork over the summers. The funding from the GSA, the Southeastern Section of GSA and the Colorado Scientific Society is greatly appreciated. I would also like to thank the departmental staff for all their help. The project on the global survey of Paleoproterozoic successions would not have been possible without selfless contributions of local geologists who shared their data and knowledge. I greatly appreciate their guidance in the field and help with the literature search. I would like to mention a few names: Jack Redden, Ed DeWitt, Kevin Chamberlain, Paul Sims, Paul Graff, Warren Day, Bryan Krapez, Nic Beukes, Pavel Medvedev, Darrel Long, Dhiraj Banerjee, Kath Grey, Richard Ojakangas, Victor Melezhik, Vasiliy Gulii, Daniel Pineyro and Gerry Bennett. Special thanks to my family iv for their love and support. It was an incredible learning experience. I am grateful for the opportunity to pursue what I thought was important and for the help from everyone along the way. v TABLE OF CONTENTS Page TITLE ........................................................................................................................i ABSTRACT ...............................................................................................................ii ACKNOWLEDGEMENTS.......................................................................................iv TABLE OF CONTENTS...........................................................................................vi LIST OF FIGURES...................................................................................................x LIST OF TABLES.....................................................................................................xii INTRODUCTION .....................................................................................................1 CHAPTER 1: CHEMOSTRATIGRAPHY OF THE PALEOPROTEROZOIC DUITSCHLAND FORMATION, SOUTH AFRICA: IMPLICATIONS FOR COUPLED CLIMATE CHANGE AND CARBON CYCLING ..............................3 ABSTRACT................................................................................................................3 INTRODUCTION .......................................................................................................3 REGIONAL GEOLOGY AND STRATIGRAPHY .....................................................6 METHODS .................................................................................................................13 RESULTS ...................................................................................................................16 EFFECTS OF DIAGENESIS AND METAMORPHISM.............................................17 THE RELATIONSHIP OF ISOTOPE ANOMALIES AND ICE AGES IN THE TRANSVAAL BASIN ................................................................................................20 CORRELATION WITH THE HURONIAN SUPERGROUP ......................................22 A PALEOPROTEROZOIC SNOWBALL EARTH?....................................................23 SPECULATION ON THE TIMING OF PALEOPROTEROZOIC ATMOSPHERIC OXYGEN RISE ..............................................................................25 CONCLUSIONS .........................................................................................................27 REFERENCES............................................................................................................27 vi CHAPTER 2: PALEOPROTEROZOIC DROWNED CARBONATE PLATFORM ON THE SOUTHEASTERN MARGIN OF THE WYOMING CRATON: A RECORD OF THE KENORLAND BREAKUP................................40 ABSTRACT................................................................................................................40 INTRODUCTION .......................................................................................................41 REGIONAL GEOLOGY AND STRATIGRAPHY .....................................................43 NASH FORK FORMATION.......................................................................................47 DESCRIPTION OF FACIES ASSOCIATIONS ..........................................................47 MASSIVE AND STROMATOLITIC DOLOMITE FACIES ASSOCIATION (L1 MEMBER).................................................................................47 HETEROLITHIC FACIES ASSOCIATION (L2 AND L7 MEMBERS) .....................48 SILICIFIED DOMAL DIGITATE STROMATOLITE FACIES ASSOCIATION (L3 AND L5 MEMBERS) ................................................................52 NODULAR DOLOMITE FACIES ASSOCIATION (L4 AND L6 MEMBERS) .........53 STROMATOLITIC DOLOMITE FACIES ASSOCIATION (L8 MEMBER)..............57 BLACK SHALE FACIES ASSOCIATION (M1 AND M3 MEMBERS).....................58 HETEROLITHIC SILICICLASTIC-NODULAR DOLOMITE FACIES ASSOCIATION (M2 MEMBER)................................................................................59 MASSIVE DOLOMITE FACIES ASSOCIATION (U1 MEMBER) ...........................60 INTERPRETATION OF DEPOSITIONAL ENVIRONMENTS .................................66