Structure and Stable Isotopic Biogeochemistry of Organic Sulfur in the Geosphere: Application of Bulk and Compound-Specific Sulfur Isotope Analysis to Modern and Ancient Euxinic SystemsO'Beirne, Molly (2019) Structure and Stable Isotopic Biogeochemistry of Organic Sulfur in the Geosphere: Application of Bulk and Compound-Specific Sulfur Isotope Analysis to Modern and Ancient Euxinic Systems. Doctoral Dissertation, University of Pittsburgh. (Unpublished) This is the latest version of this item.
AbstractOrganic sulfur (OS) is the second largest pool of reduced sulfur in the environment after pyrite and is a topic of interest as it has considerable connections to petroleum formation; the global biogeochemical cycles of sulfur, carbon, oxygen, and iron; microbial activity; and organic matter preservation through geologic time. Despite these connections, our understanding of OS formation and occurrence is limited and therefore, interpretations of the geologic record based on changes in the relative abundances of inorganic, organic, and elemental sulfur are also limited. The research presented here is one of the first to use measured variations in the stable sulfur isotope composition (δ34S) of inorganic sulfur species and OS (at the bulk and molecular level) to investigate OS formation on multiple timescales in both the laboratory and natural environment. Results of this research are multifold. First, we demonstrate the ability to measure polysulfide speciation via gas chromatography (GC) at sub-micromolar levels and with good precision in both laboratory and environmental samples. With a bit more refinement, our method of analysis can be used for direct compound-specific sulfur isotope analysis (CSSIA) of individual polysulfide species using a GC coupled to a multi-collector ICP-MS (GC/MC-ICP-MS). Such measurements could provide valuable information on the role polysulfides play in the natural environment. Second, detailed structural (i.e. FT-IR and online pyrolysis) and δ34S analysis of reaction products from laboratory experiments involving the abiotic sulfurization of carbohydrates and natural dissolved organic matter provides experimental evidence for the structural and sulfur isotopic relationships between reactive inorganic sulfur species and OS in the geosphere. Lastly, we show the utility of paired pyrite and OS isotope records in reconstructing paleoenvironmental conditions. δ34S values of pyrite and OS from the Jurassic aged Blackstone Band of the Kimmeridge Clay Formation display dynamic fluctuations that are related to variations in microbial sulfate reduction rates, which may be influenced by the formation of macromolecular OS during times of increased organic carbon burial. CSSIA of bitumen and kerogen-pyrolysates reveals more complex dynamics, where bitumen compounds record a sulfur source unrelated to bulk OS and kerogen compounds reflect the δ34S of bulk OS. Share
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