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NOV 2 2 2011 SEPTEMBER 2011 LIBRARIES ( 2011 Massachusetts Institute of Technology All Rights Reserved Organic Geochemistry and Stable Isotope Constraints on Precambrian Biogeochemical Processes by Katherine S. Thomas SUBMITTED TO THE DEPARTMENT OF EARTH, ATMOSPHERE AND PLANETARY SCIENCES IN THE PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE IN GEOCHEMISTRY ARCHIVES AT THE MASSACHUSETTS INSTITUTE OF TECHAOLOGY MASSACHUSETTS INSTITUTE OF TECHNOLOGY NOV 2 2 2011 SEPTEMBER 2011 LIBRARIES ( 2011 Massachusetts Institute of Technology All rights reserved The author hereby grants to M.I.T. permission to reproduce and distribute publicly paper and electronic copies of this thesis and to grant others the right to do so. Signature of Author.................... ............ .. ...... ........ Department of Earth, Atmospheric and Planetary Sciences September 2011 Certified by............ Shuhei Ono Assistant Professor of Geochemistry Thesis Supervisor Accepted by.......... ........................................ Maria Zuber E.A Griswold Professor of Geophysics Head of Department Organic Geochemistry and Stable Isotope Constraints on Precambrian Biogeochemical Processes: Examples of the Late Proterozoic Coppercap Formation, NWT Canada and Archean Gorge Creek Group, Pilbara by Katherine S. Thomas Submitted to the Department of Earth, Atmospheric and Planetary Sciences on July 15, 2011 in Partial Fulfillment of the Requirements for the Degree of Masters of Science in Earth, Atmospheric and Planetary Sciences Abstract Details of the biogeochemical cycles and the dominant mechanisms present in Precambrian remain heavily debated topics. The events of the Late Proterozoic onset to glaciations and what types of early life existed in the Archean are two of the many provoking topics within the Precambrian. We set out to improve the understanding of these geologic intervals by examining stable isotopic signatures and molecular fossils (biomarkers) in Late Proterozoic and Mesoarchean ages sedimentary rocks in Northwestern Territories, Canada and Pilbara, Western Australia, respectively. This thesis presents sulfur, carbon, oxygen and nitrogen stable isotopic data along with distribution of steranes and hopanes biomarkers. Geochemical data is analyzed in the context of elucidating the key biological and environmental factors involved in the Mesoarchean marine biosphere and the Late Proterozoic onset of glaciations. Stable isotopic analysis of the Gorge Creek Group in Pilbara, Western Australia reveals organisms capable of microbial sulfur disproportionation were likely the dominant biological players in Mesoarchean deep-ocean sulfur cycling. Biomarker and isotopic proxies of the Coppercap Formation reveal diverse biological activity directly prior to the Sturtian Glaciation with communities of green and purple sulfur bacteria as well as methanotrophs and cyanobacteria. Possible environmental implications of these communities co-existing are explained in context of changes in ocean chemistry and the diversification of eukaryotic life. Thesis Supervisor: Shuhei Ono Tide: Assistant Professor of Geochemistry 4 Acknowledgements I am eternally grateful for the generous support and encouragement of my extended community of advisors, coworkers, family and friends. The foremost thanks go to Shuhei Ono, my thesis advisor. Professor Ono's assistance in the lab, willingness to discuss material, commentary, and support demonstrate his dedication to his students and their research. A very large thank you goes to Dr. Christian Hallmann for all his help in the preparation of this thesis, guidance, friendship and encouragement throughout the process. I would like to thank Dr. Francis Macdonald for his collaboration, valuable discussions and endless enthusiasm. Finally, I would also like to show my great appreciation to Roger Summons and Tanja Bosak, for their insight, excitement and support that lead me to study geobiology initially, as well as continue my studies. I would also like to thank Andrew Whitehill, Harry Oduro and Jon Grabenstatter for comments on my thesis work and all the wonderful people of E25 for their discussions, smiles and for providing the most nurturing work environment I can imagine. I would like to recognize M. Jansen, T. Goff, A. LeMessurier, N. Hanselmann, M. Sori, my parents and my housemates for being there for me every step of the way. This thesis is written in the memory of my great uncle Robert Thomas who passed away June, 2010. I will always remember him for his eloquent letters, his whimsical stories and as being a constant source of inspiration and encouragement to all those around him. Table of Contents Abstract........................................................................................................................................... 3 Acknow ledgem ents......................................................................................................................... 5 Chapter 1 Introduction:............................................................................................................ 9 1.1 Thesis Outline ................................................................................................................ 11 Chapter 2: Analytical Background............................................................................................ 13 2.1 Sulfur................................................................................................................................... 14 2.2 Carbon................................................................................................................................. 18 2.3 Lipid Biom arker Analysis................................................................................................. 19 2.3.1 Pristane and Phytane................................................................................................. 20 2.3.2 Chrom atiaceae and Chlorobiaceae........................................................................... 21 2.3.3 C30 Steranes............................................................................................................ 22 2.3.4 2-M ethyl hopanoids and 3-M ethyl hopanoids ....................................................... 23 Chapter 3 Experim ental Procedures.......................................................................................... 24 3.1 Sam pling ............................................................................................................................. 24 3.2 Sam ple Preparation .......................................................................................................... 24 3.3 Sulfur Isotope Analysis:................................................................................................... 25 3.4 Carbon Isotope, Total Organic Carbon and Carbonate Weight percent analysis ............ 28 3.5 M olecular Biological M aterial Analysis......................................................................... 29 Chapter 4 Gorge Creek: ............................................................................................................ 33 Abstract..................................................................................................................................... 33 4.1 Introduction:........................................................................................................................ 33 4.2 Gorge Creek Geologic Background:................................................................................ 34 4.3 Results................................................................................................................................. 36 4.4 Discussion:.......................................................................................................................... 43 4.4.1 Diagenetic concerns:.............................................................................................. 43 4.4.2 Deep M arine environm ent: ....................................................................................... 44 4.4.5 Sulfur Concentrations and M ultiple Sulfur Isotopes ................................................ 46 Conclusion ................................................................................................................................ 50 Chapter 5: Coppercap Form ation............................................................................................... 52 Abstract:.................................................................................................................................... 52 5.1 Introduction......................................................................................................................... 53 6 5.2 Geologic Setting.................................................................................................................. 53 5.3 Results................................................................................................................................. 58 5.4 D iscussion:.......................................................................................................................... 74 5.4.1 D iagenetic Considerations:...................................................................................... 74 5.4.2 3Cearb and 6 3 COrg..............................................................................................--...-- 77 5.4.3 S34SCAS, 834Spyrite, A 3 S and A36S....................................... 80 5.4.5 M olecular Biom arkers .............................................................................................. 84 5.4.6 Environm
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