Carbonate Geochemistry of Marine Authigenic Carbonates and Host Sediments: Exploring Mineral Formation Pathways and Organic Preservation Potential in Modern Sediments
Abstract
Ancient authigenic dolomites (e.g., concretions) have been long studied in order to determine formation conditions and provide insight into shallow diagenetic environments. The formation of these dolomites is commonly attributed to the anaerobic microbial degradation of organic matter (a process that can increase the local pore water alkalinity), based on carbon isotope as well as other geochemical data. Authigenic dolomites also occur in modern, "still soft" sediments rich in organic matter. However, a comprehensive carbon isotopic characterization of these precipitates has yet to be conducted. Preliminary data show a wide range of δ13C values (about -11 to +12‰). Positive values that typify dolomites of the Gulf of California and the southwestern African margin indicate methanogenesis. Dolomites of the Peru margin and Cariaco Basin yield negative values that may represent a variety of organic matter degradation mechanisms. Regardless of specific mechanisms, organic matter degradation can promote authigenesis. Ultimately, mineralization encases primary sedimentary components and may act to preserve organic matter from subsequent degradation due to permeability reduction resulting from cementation. Concretionary carbonates have been found to preserve macro and micro fossils, metastable sedimentary grains, magnetic minerals, sedimentary structures, various specific organic compounds, and overmature organic matter exposed in outcrop. However, a similar protective relationship has not been demonstrated for disseminated, bulk organic matter in still-soft sediments. The study of these sediments 1) reveal the relationship between organic carbon degradation and authigenesis and 2) may provide insight into the potential of cementation to preserve organic matter during subsequent burial.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMPP11A1995S
- Keywords:
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- 1039 Alteration and weathering processes;
- GEOCHEMISTRYDE: 1050 Marine geochemistry;
- GEOCHEMISTRYDE: 4805 Biogeochemical cycles;
- processes;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4924 Geochemical tracers;
- PALEOCEANOGRAPHY