Intertwined Fates of Metals, Sulfur, and Organic Carbon in Black Shales
Lisa M. Pratt, Cara L. Davis, 1992. "Intertwined Fates of Metals, Sulfur, and Organic Carbon in Black Shales", Geochemistry of Organic Matter in Sediments and Sedimentary Rocks, Lisa M. Pratt, John B. Comer, Simon C. Brassell, Ruth Droppo
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When the input rate of readily degradable organic matter exceeds the replenishment rate of oxygen in marine sediments, anoxic environments develop. During anoxic diagenesis, the sediment system becomes a reservoir for sulfur due to reduction-oxidation reactions associated with communities of anaerobic bacteria. Concentrations of metals and organic carbon are covariant in many black muds and shales due to 1) direct chemical complexing of metal ions with hetero-atomic functional groups on thermally immature organic matter and/or 2) reduction of sulfate and metals using organic substrates as an electron donor and resulting in precipitation of metallic sulfides or elemental metals. Early diagenetic formation of metallo- and sulfuro-organic ligands plays an important role in selective preservation of specific organic compounds. Future research will reveal the extent to which such processes influence the overall preservation of organic matter in sediments and sedimentary rocks.
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As both researchers and educators, the authors have faced the difficult task of lecturing on the subject of organic geochemistry to an audience that is genuinely interested in but unable to keep pace with this rapidly advancing field. The technical jargon makes it difficult to become engaged with the topic of geochemistry without a major investment in background readings. This volume was written specifically for the graduate student or professional geoscientist needing a brief but reasonably comprehensive review of the potential applications of organic geochemical data to geological studies. This volume is divided into three sections. Section I, organic matter is viewed as a highly reactive constituent of soil, water column and sediment. Section II, the focus is on the molecular constituents of geological materials and their ability to record the history of changes in organic matter ranging from its biological formation, through sediment deposition and compaction, to its modification under the thermal stress of diagenesis and maturation. Section III, changes in the composition of organic matter in buried sediments are discussed in terms of chemical kinetics.