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Carbon and Sulfur Cycling in Early Paleozoic Oceans University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 5-2011 Carbon and Sulfur Cycling in Early Paleozoic Oceans Cara Kim Thompson [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Part of the Geochemistry Commons, and the Geology Commons Recommended Citation Thompson, Cara Kim, "Carbon and Sulfur Cycling in Early Paleozoic Oceans. " PhD diss., University of Tennessee, 2011. https://trace.tennessee.edu/utk_graddiss/1033 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Cara Kim Thompson entitled "Carbon and Sulfur Cycling in Early Paleozoic Oceans." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a major in Geology. Linda C. Kah, Major Professor We have read this dissertation and recommend its acceptance: Chris Fedo, Kula Misra, Lee Cooper Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) To the Graduate Council: I am submitting herewith a dissertation written by Cara Kim Thompson entitled “Carbon and Sulfur Cycling in Early Paleozoic Oceans”. I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, with a major in Geology. Linda C. Kah, Major Professor We have read this dissertation and recommend its acceptance: Chris Fedo Kula Misra Lee Cooper Accepted for the Council: Carolyn R. Hodges Vice Provost and Dean of the Graduate School (Original signatures are on file with official student records) CARBON AND SULFUR CYCLING IN EARLY PALEOZOIC OCEANS A Dissertation Presented for the Doctor of Philosophy Degree The University of Tennessee, Knoxville Cara Kim Thompson May 2011 Dedication This dissertation is dedicated to my grandfather, Thomas W. Schoelen, who first sparked my interest in science, encouraged me not to sell myself short, and inspired me to reach my fullest potential. I am finally Dr. Doogie! ii Acknowledgements I would like to thank everyone who offered assistance to help me complete this Doctor of Philosophy degree in Geology. I would like to thank Linda Kah for all of her helpful insight and guidance as I worked through my dissertation research. I would also like to thank my committee members, Chris Fedo, Kula Misra, and Lee Cooper for their insight and support, and in particular Kula for agreeing to join my committee at a late date and for also serving on my Master of Science committee and Lee, who made a special trip to Knoxville for my defense. Most importantly, I would like to thank my parents, Thomas and Trina Thompson, my brother, Kevin Thompson, my grandmother, Bonnie Schoelen, and my husband, Craig, for all of their love and support during these many long years in graduate school. Finally, I would like to thank Vincent for reminding me to relax and take a walk every once in a while. iii Abstract Here, I evaluate biospheric evolution during the Ordovician using high-resolution inorganic carbon and sulfur (carbonate-associated sulfate and pyrite) isotope profiles for Early Ordovician to early Late Ordovician strata from geographically distant sections in Western Newfoundland and the Argentine Precordillera. Additionally, I present new, high-resolution U-Pb ages for volcanic ash beds within strata of the Argentine Precordillera. Carbon isotope data record subdued variation that is typical of Early to Middle Ordovician strata worldwide. By contrast, sulfur isotopic compositions of carbonate-associated sulfate reveal a complex signal of short- term, rhythmic variation superimposed over a longer-term signal. This short-term, rhythmic variation occurs in all sections and appears to be unrelated to lithology or depositional environment, suggesting preservation of an oceanographic signal. I interpret this signal to reflect a combination of a marine sulfate reservoir that was likely much smaller than the modern, the persistence of a substantial deep-ocean hydrogen sulfide reservoir, and the episodic oxidation of a portion of the deep-ocean euxinic reservoir. Persistent euxinia likely resulted from decreased solubility of oxygen in warmer water and/or sluggish oceanic circulation during greenhouse conditions that reduced vertical ventilation. A dramatic change in the behavior of carbonate- associated sulfate and pyrite in the Middle Ordovician is interpreted to reflect a major oceanographic event that records the initial transition from Ordovician greenhouse to icehouse states. I suggest that the initiation of downwelling of increasingly cool, oxygen-rich surface water resulted in widespread oxidation of much of the deep ocean hydrogen sulfide reservoir and concomitant limitation of marine pyrite formation. It is unknown, however, why sea surface temperatures declined through the Early to Middle Ordovician. Explosive volcanism does not appear to be a primary climate driver, based on the timing of Argentinian K-bentonite formations relative to marine records of sea surface temperature, carbon and strontium isotopic composition. Rather, long-term positive feedback between organic carbon burial rates and productivity may have increased carbon dioxide drawdown, ultimately driving a gradual decrease in sea surface temperatures in the Early to Middle Ordovician. iv Table of Contents Page Part 1: Introduction.......................................................................................................................1 1. Overview.....................................................................................................................................2 2. The Ordovician carbon and sulfur isotope records................................................................2 3. Relationship between K-bentonite deposition and climate....................................................4 4. Summary.....................................................................................................................................5 References cited..............................................................................................................................5 Part 2: Sulfur isotope evidence for widespread euxinia and a fluctuating oxycline in Early to Middle Ordovician greenhouse oceans............................................................9 Abstract.........................................................................................................................................10 1. Introduction..............................................................................................................................11 2. Geologic setting and biostratigraphy.....................................................................................16 2.1. Ordovician paleogeography.................................................................................................16 2.2. Argentine Precordillera........................................................................................................17 2.2.1. La Silla Formation.............................................................................................................20 2.2.2. San Juan Formation..........................................................................................................20 2.3. Western Newfoundland........................................................................................................23 2.3.1. Aguathuna Formation.......................................................................................................25 2.3.2. Table Head Group.............................................................................................................25 3. Methods.....................................................................................................................................26 3.1. Petrographic screening.........................................................................................................26 3.2. Major and trace element analyses.......................................................................................30 3.3. Total organic carbon concentration....................................................................................30 3.4. Carbon and oxygen isotope analyses...................................................................................31 3.5. Sulfur extraction and isotope analyses................................................................................31 4. Results and interpretation.......................................................................................................33 4.1. Geochemical signals of alteration........................................................................................33 4.1.1. δ 18O and trace element data.............................................................................................38 v 34 4.1.2. δ SCAS signal......................................................................................................................40
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