UNLV Theses, Dissertations, Professional Papers, and Capstones 12-2010 Carbon isotopic fractionation across a late Cambrian carbonate platform: A regional response to the SPICE event as recorded in the Great Basin Jonathan Lloyd Baker University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Biogeochemistry Commons, Geochemistry Commons, and the Geology Commons Repository Citation Baker, Jonathan Lloyd, "Carbon isotopic fractionation across a late Cambrian carbonate platform: A regional response to the SPICE event as recorded in the Great Basin" (2010). UNLV Theses, Dissertations, Professional Papers, and Capstones. 681. http://dx.doi.org/10.34917/1887413 This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). 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CARBON ISOTOPIC FRACTIONATION ACROSS A LATE CAMBRIAN CARBONATE PLATFORM: A REGIONAL RESPONSE TO THE SPICE EVENT AS RECORDED IN THE GREAT BASIN, UNITED STATES by Jonathan Lloyd Baker Bachelor of Science Weber State University 2008 A thesis submitted in partial fulfillment of the requirements for the Master of Science in Geoscience Department of Geoscience College of Science Graduate College University of Nevada, Las Vegas December 2010 Copyright by Jonathan Lloyd Baker 2011 All Rights Reserved THE GRADUATE COLLEGE We recommend the thesis prepared under our supervision by Jonathan Lloyd Baker entitled Carbon Isotopic Fractionation across a Late Cambrian Carbonate Platform: A Regional Response to the SPICE Event as Recorded in the Great Basin be accepted in partial fulfillment of the requirements for the degree of Master of Science in Geoscience Ganquig Jiang, Committee Chair Matthew Lachniet, Committee Member Rodney Metcalf, Committee Member Peter Starkweather, Graduate Faculty Representative Ronald Smith, Ph. D., Vice President for Research and Graduate Studies and Dean of the Graduate College December 2010 ii ABSTRACT Carbon Isotopic Fractionation Across A Late Cambrian Carbonate Platform: A Regional Response To The SPICE Event As Recorded In The Great Basin, United States by Jonathan Lloyd Baker Dr. Ganqing Jiang, Examination Committee Chair Associate Professor of Geoscience University of Nevada, Las Vegas Geochemical models have suggested that the late Cambrian was characterized by a greenhouse climate with high pCO2. Furthermore, stable- isotope analyses within the Great Basin have documented a large carbonate 13 isotope (δ Ccarb) excursion, known as the Steptoean Positive Carbon Isotope Excursion (SPICE). This event has been documented globally, and is interpreted as having resulted from enhanced organic carbon burial. Unless the size of carbon reservoirs in the Cambrian ocean was significantly different from those of the Cenozoic, this forcing should have resulted in a comparable carbon-isotope 13 excursion in organic matter (δ Corg). It is also predicted that increased organic carbon burial would lower atmospheric CO2, which may cause global cooling and a reduction in carbonate-organic carbon isotope fractionation. To test these predictions, paired carbonate and organic carbon isotope data are reported here from carbonate stratigraphic sections at Shingle Pass, Nevada and in House 13 Range, Utah. At Shingle Pass, δ Corg values record a positive excursion that 13 roughly mirrors δ Ccarb values at a similar magnitude, suggesting an oceanographic control on the carbon isotope trend. In the House Range section, iii 13 although δ Corg values show a rough positive shift associated with positive 13 δ Ccarb, the magnitude is smaller and values show minor shifts across the excursion. However, constructing a time-equivalent overlay of data from both sections using key stratigraphic boundaries resolved apparent discrepancies, suggesting a regional control on carbon isotopic fractionation. The difference 13 13 13 between carbonate and organic carbon isotope values (Δ C = δ Ccarb – δ Corg) averages 27‰ to 28‰ in both sections, but increases to 30‰ at the peak of the excursion and falls to as low as 25‰ immediately after the Sauk II/III sequence boundary. Temporal variations in Δ 13C do not follow the predicted atmospheric 13 CO2 changes before the δ Ccarb peak of the SPICE, as might have been derived from the increased organic carbon burial model for the origin of the SPICE event, and indicates that the carbon isotope fractionation was less sensitive to 13 atmospheric CO2 changes when ambient CO2 was high. The abrupt drop in Δ C 13 after the δ Ccarb peak of the SPICE is consistent with low atmospheric CO2 and the potential evolution of photosynthetic organisms in adapting to CO2-limited environments with stronger bicarbonate uptake during carbon fixation. iv ACKNOWLEDGEMENTS Foremost, I would like to thank my advisor, Dr. Ganqing Jiang, for introducing me to the discipline of chemostratigraphy and the problems related to this thesis. Through much patience and diligence, you have remained devoted to my progress beyond what I deserved. Moreover, you have inspired me to pursue my academic goals with confidence, though in a spirit of humility and self- awareness that will never leave me. Above all, you have always taught me to stay happy and healthy, regardless of the challenges that face me. I am grateful to the Department of Geoscience at UNLV for the opportunity to study in such a unique environment, replete with camaraderie and a healthy zeal for scientific endeavor. In particular, I would like to thank Dr. Andrew Hanson, both for introducing me to the department and for helpful discussions concerning the strength of my data. Thank you also to Dr. Margaret (Peg) Rees for spending many days guiding me through the field area and offering your expertise and direction in the early stages of this manuscript. Additionally, I would like to recognize the other members of my advisory committee — Dr. Matt Lachniet, Dr. Rod Metcalf, and Dr. Peter Starkweather — for the time and effort spent reviewing this project and providing vital feedback toward the completion thereof. I greatly appreciate your support, and the time vested to discussing various topics related to this thesis on an individual basis. It has thus far been an honor to be a part of the “Carbonate Mafia”, and I am especially thankful to fellow members thereof. To Adam “Cycle Master” Zeiza and Ratna “Wiwid” Widiarti, I am indebted to you both for your assistance in the v field, without which I could not have completed this project. I thank you also for sharing your expertise, and believe that your passion and discipline have made me a better field researcher. Thank you to Swapan Sahoo and Bobby Henry for assistance and motivation during laboratory analyses, as well as many helpful discussions in the interpretation of my data. Special thanks goes to my undergraduate advisor, Dr. Jeff Eaton, whose unrivaled passion for field research originally inspired me to pursue a graduate degree, and whose confidence in my success proved a turning point when I doubted myself. Thanks also to my good friend Matthew Weinstock, who has taught me more than anyone what it means to be a scientist and a researcher, and to Samuel Emadi, who has never failed to remind me that no matter how busy or overwhelmed I think I am, I am simply not. Last, but not least, I wish to thank my beautiful wife, Natasha, for her unfailing love, care, and affection, but especially for her sacrifice when I have often been present in body, though absent in spirit. You have lifted me up and given me ample motivation to pursue my goals. Bol’shoe spasibo, dorogaya Natusya. This thesis was made possible through funding from the Department of Geoscience at UNLV, the Geological Society of America, the Nevada Petroleum Society, and Dr. Ganqing Jiang. Special thanks also to Dr. Adolph Yonkee for providing equipment for petrographic analysis at Weber State University. vi TABLE OF CONTENTS ABSTRACT iii ACKNOWLEDGEMENTS v LIST OF FIGURES ix CHAPTER 1 INTRODUCTION 1 CHAPTER 2 GEOLOGIC BACKGROUND 4 2.1 Overview of field localities within this study 4 2.1.1 Shingle Pass 4 2.1.2 House Range 6 2.2 Paleogeography and sedimentary framework 6 2.3 Steptoean stage nomenclature, biostratigraphy, and relation 10 to trilobite extinction CHAPTER 3 BACKGROUND ON CARBON ISOTOPES AND 13 PALEOCLIMATE 3.1 Applicability of paired carbon isotope analysis to 13 paleoclimatology 3.2 Organic carbon contribution from secondary producers 16 3.3 Local environmental controls on carbon isotopic values 17 3.4 Diagenetic modification of δ13C 18 CHAPTER 4 PREVIOUS WORK 20 4.1 Global documentation of the SPICE event 20 4.2 Interpretations regarding the forcing mechanism of the 21 SPICE event 13 4.3 Reported values of δ Corg during the SPICE event 22 4.4 δ34S, organic burial, and the SPICE event 23 CHAPTER 5 METHODS 25 5.1 Stratigraphic sections and sampling 25 5.2 Sample preparation for isotopic analysis 26 13 18 5.3 Inorganic