Clay Mineralogy, Organic Carbon Burial, and Redox Evolution in Proterozoic Oceans

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Clay Mineralogy, Organic Carbon Burial, and Redox Evolution in Proterozoic Oceans

Show simple item record Tosca, Nicholas J. Johnston, David T Mushegian, Alexandra Arcadievna Rothman, Daniel H. Summons, Roger E. Knoll, Andrew Herbert 2010-04-13T14:35:16Z 2010
dc.identifier.citation Tosca, Nicholas J., David T. Johnston, Alexandra Arcadievna Mushegian, Daniel H. Rothman, Roger E. Summons, and Andrew Herbert Knoll. 2010. Clay mineralogy, organic carbon burial, and redox evolution in Proterozoic oceans. Geochimica et Cosmochimica Acta 74(5): 1579-1592. en_US
dc.identifier.issn 0016-7037 en_US
dc.description.abstract Clay minerals formed through chemical weathering have long been implicated in the burial of organic matter (OM), but because diagenesis and metamorphism commonly obscure the signature of weathering-derived clays in Precambrian rocks, clay mineralogy and its role in OM burial through much of geologic time remains incompletely understood. Here we have analyzed the mineralogy, geochemistry and total organic carbon (TOC) of organic rich shales deposited in late Archean to early Cambrian sedimentary basins. Across all samples we have quantified the contribution of 1M and 1Md illite polytypes, clay minerals formed by diagenetic transformation of smectite and/or kaolinite-rich weathering products. This mineralogical signal, together with corrected paleo-weathering indices, indicates that late Archean and Mesoproterozoic samples were moderately to intensely weathered. However, in late Neoproterozoic basins, 2M1 illite/mica dominates clay mineralogy and paleo-weathering indices sharply decrease, consistent with an influx of chemically immature and relatively unweathered sediment. A late Neoproterozoic switch to micaceous clays is inconsistent with hypotheses for oxygen history that require an increased flux of weathering-derived clays (i.e., smectite or kaolinite) across the Precambrian–Cambrian boundary. Compared to previous studies, our XRD data display the same variation in Schultz Ratio across the late Neoproterozoic, but we show the cause to be micaceous clay and not pedogenic clay; paleo-weathering signals cannot be recovered from bulk mineralogy without this distinction. We find little evidence to support a link between these mineralogical variations and organic carbon in our samples and conclude that modal clay mineralogy cannot by itself explain an Ediacaran increase in atmospheric oxygen driven by enhanced OM burial. en_US
dc.description.sponsorship Organismic and Evolutionary Biology en_US
dc.language.iso en_US en_US
dc.publisher Elsevier en_US
dc.relation.isversionof doi:10.1016/j.gca.2009.12.001 en_US
dash.license OAP
dc.subject organic carbon en_US
dc.subject Proterozoic en_US
dc.subject oxygen en_US
dc.subject clay en_US
dc.subject mineralogy en_US
dc.subject sedimentary geochemistry en_US
dc.title Clay Mineralogy, Organic Carbon Burial, and Redox Evolution in Proterozoic Oceans en_US
dc.type Journal Article en_US
dc.description.version Accepted Manuscript en_US
dc.relation.journal Geochimica et Cosmochimica Acta en_US Knoll, Andrew Herbert 2010-04-13T14:35:16Z

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