u Ottawa L'Universite canadieniie Canada's university FACULTE DES ETUDES SUPERIEURES 1^=1 FACULTY OF GRADUATE AND ET POSTOCTORALES U Ottawa POSDOCTORAL STUDIES L'Umversitd canadiemie Canddd'b university Sarah Elizabeth Agosta "XUTEMDEIXTWSE7XUTHORWTHKTS"' M.Sc. (Geography) GRADE/DEGREE Department of Geography FACULTE, ECOLE, DEPARTEMENT / FACULTY, SCHOOL, DEPARTMENT Preservation and Diagenesis in Ancient Speleothems: Evidence from Bear Cave, Yukon Territory TITRE DE LA THESE / TITLE OF THESIS Bernard Lauriol „._„___„„„__.„.^ Ian D. Clark „„„„„„..„___._.„„„„ Joyce Lundberg Andre Viau Gary W. Slater Le Doyen de la Faculte des etudes superieures et postdoctorales / Dean of the Faculty of Graduate and Postdoctoral Studies Preservation and diagenesis in ancient speleothems: evidence from Bear Cave, Yukon Territory Sarah Agosta Thesis presented to the Faculty of Graduate and Postdoctoral Studies in partial fulfillment of the requirements for the degree of Master of Science in Physical Geography Department of Geography Faculty of Arts University of Ottawa Supervisors: Dr. Bernard Lauriol (Department of Geography) Dr. Ian D. Clark (Department of Earth Sciences) Thesis Committee: Dr. Andre Viau (Department of Geography, University of Ottawa) Dr. Joyce Lundberg (Department of Geography, Carleton University) © Sarah Agosta, Ottawa, Canada, November 2010. 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The author retains copyright L'auteur conserve la propriete du droit d'auteur ownership and moral rights in this et des droits moraux qui protege cette these. Ni thesis. Neither the thesis nor la these ni des extra its substantiels de celle-ci substantial extracts from it may be ne doivent etre imprimes ou autrement printed or otherwise reproduced reproduits sans son autorisation. without the author's permission. In compliance with the Canadian Conformement a la loi canadienne sur la Privacy Act some supporting forms protection de la vie privee, quelques may have been removed from this formulaires secondaires ont ete enleves de thesis. cette these. While these forms may be included Bien que ces formulaires aient inclus dans in the document page count, their la pagination, il n'y aura aucun contenu removal does not represent any loss manquant. of content from the thesis. 1+1 Canada Abstract Speleothems are rare in high-latitude and high-altitude caves, which is why Bear Cave in the north-western Yukon Territory is particularly unique, as it houses some of the oldest and highest latitude speleothem in the world. In this study, a detailed petrographic and geochemical study was conducted along the profile of a 68-cm long late-Miocene flowstone from Bear Cave (BC1) to reveal the processes that took place at the time of deposition, in addition to those that followed, in aims to determine its paleoclimatic suitability. These studies suggest that softer facies are generally representative of disequilibrium conditions, where in-filled textures provide evidence for diagenic phenomena; these processes ultimately obscure the original climate signal, compromising the integrity of the flowstone in terms of its paleoclimatic suitability. Conversely, harder facies are likely deposited in isotopic equilibrium and resistant to post-depositional diagenesis, and are therefore more reliable for detailed paleoclimatic analysis. The variability of the calcite sequences in the profile of BC1 imply that environmental conditions have been considerably variable of the course of deposition, reflecting alternating cool/dry (softer facies) and warm/wet (harder facies) climatic conditions. Results from radiogenic 4He-dating constrain the timeframe of deposition, with ages centering around 9.35 ± 0.52 Ma, which are in line with regional geomorphic interpretations. This study emphasizes the importance of a complimentary petrographic study in speleothem geochemical studies used in paleoclimatic and paleoenvironmental research. 11 Acknowledgements This project would not have been possible without funding from NSERC (Natural Sciences and Engineering Research Council of Canada), NSTP (Northern Scientific Training Program), PCSP (Polar Continental Shelf Project) and the University of Ottawa. Several people have also been instrumental in allowing this project to be completed. Special thanks to Dr. P. Middlestead from the G.G. Hatch laboratory, Dr. R. Mohapatra from the MAPL Noble Gas laboratory, and Dr. N. DeSilva from the Department of Earth Sciences at the University of Ottawa for their invaluable assistance in and outside of the lab. I must also acknowledge Dr. D. Lacelle for his counsel, Dr. T. Kluge and Dr. Werner Aeschbach-Hertig from the Department of Environmental Physics at the University of Heidelberg in Germany for their work on initial 4He-dating on the BC1 flowstone, as well as Dr. D. Pinti & Dr. B. Ghaleb from UQAM for their additional discussion and measurements of 4He-dating. My sincere gratitude is extended to the members of my committee, Dr. A. Viau and Dr. J. Lundberg, for their insightful comments and suggestions. I must especially thank my research supervisors, Dr. B. Lauriol and Dr. I.D. Clark. I am forever indebted for their encouragement, patience, and guidance throughout the duration of this project, as well as the many opportunities that have been bestowed to me over the course of my two years at the University of Ottawa. It has been an honour being one of your students. A warm message of thanks goes out to all my friends (too many to list here but you know who you are!) for providing the support and friendship that I needed to keep my sanity over the past two years. To my hard-working parents, Jo-Ann & Corrado, who sacrificed their lives for my sister and myself, I thank them for their unconditional love and care. To my wonderful sister Emily, who has become my best friend, I thank her for all her advice and support. I would not have made it this far without them and I love them all dearly. And finally, to Ken, thank you for always having faith in me, giving me the inspiration and motivation for completing this thesis, and periodically reminding me of my nerdy love of rocks...I love you. in Table of Contents Abstract n Acknowledgments 111 Table of Contents IV List of Figures vi List of Tables IX Introduction 1 1 1 Thesis Structure & Research Objectives 2 1 2 Speleothem development and preservation 5 1 2 1 Depositional mechanisms 5 1 2 2 Post-depositional diagenesis and recrystalhzation 7 1 2 3 Geographical context 8 1 3 Structure and composition of speleothems 9 1 3 1 Mineralogy, crystal morphology and environmental conditions of formation 9 1 3 2 Colour, form and rates of growth 11 1 4 Geochemistry 12 1 4 1 Stable isotope studies 6180 and 613C 12 142 Equilibrium vs non-equilibnum deposition 15 1 4 3 Trace element studies 18 1 5 Dating techniques applied to ancient speleothems 20 Regional Setting & Sample Description 23 2 1 Bear Cave, Yukon Territory 23 2 1 1 Geology 23 2 1 2 Regional climate and vegetation past and present 27 2 2 BC1 flowstone 30 Methodology 33 3 1 Petrography 33 3 1 1 Crystallography study 33 3 1 2 Scanning Electron Micrography 34 3 2 Geochemistry 34 3 2 1 Stable isotope profile (613C & S180) 34 3 2 2 High-resolution geochemistry (trace elements & stable isotopes) 35 3 3 Chronology building 37 3 3 1 Epi-fluorescent spectroscopy 37 iv 3 3 2 Paleomagnetism 37 3 3 3 Radiogenic He-dating 38 Results & Analysis 42 4 1 Petrography 42 4 11 Crystallographic study 42 4 1 2 Scanning Electron Micrography 47 4 1 3 Summary 50 4 2 Geochemistry 51 4 2 1 Stable isotope profile (5I3C & 5I80) 51 422 Isotopic signatures of BC1 microfabncs 58 4 2 3 High-resolution geochemistry 63 4 24 Summary 71 4 3 Chronology building 72 4 3 1 Epi-fluorescence 72 4 3 2 Paleomagnetism 75 4 3 3 Radiogenic He-datmg 76 4 3 4 Summary 79 Discussion & Interpretation 80 5 1 Paleochmatic suitability of the BC1 flowstone 80 5 1 1 Evidence tor disequilibrium conditions, recrystallization and diagenesis 80 5 1 2 Reliable microfabncs for paleo-interpretation 85 5 2 Interpretation of the depositional history at Bear Cave Mountain 89 5 2 1 Crystal growth mechanisms and environmental conditions of formation 89 5 2 2 Paleochmatic and paleoenvironmental significance 92 5 3 Age estimates for the BC1 flowstone 97 5 3 1 Bear Cave in relation to regional geomorphic evolution 97 532 Paleomagnetic stratigraphy 101 53 3 Challenges of dating ancient speleothems 103 Summary & Conclusion 107 References 110 Appendix I - Petrographic transects 118 Appendix II - ICP-AES procedural methodology 123 Appendix