Preservation of overmature, ancient, sedimentary organic matter in carbonate concretions during outcrop weathering

Concretions are preferentially cemented zones within sediments and sedimentary rocks. Cementation can result from relatively early diagenetic processes that include degradation of sedimentary organic compounds or methane as indicated by significantly 13C‐depleted or enriched carbon isotope compositi...

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Bibliographic Details
Published in:Geobiology 2017-01, Vol.15 (1), p.146-157
Main Author: Loyd, S. J.
Format: Article
Language:English
Subjects:
Carbon
Carbon Isotopes - analysis
Carbonates - analysis
Concretions
Geologic Sediments - chemistry
Inorganic carbon
Isotopes
Membrane permeability
Minerals
Organic Chemicals - analysis
Organic compounds
Organic matter
Preservation
Pyrite
Sediments
Shale
Total organic carbon
Weathering
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Summary:Concretions are preferentially cemented zones within sediments and sedimentary rocks. Cementation can result from relatively early diagenetic processes that include degradation of sedimentary organic compounds or methane as indicated by significantly 13C‐depleted or enriched carbon isotope compositions. As minerals fill pore space, reduced permeability may promote preservation of sediment components from degradation during subsequent diagenesis, burial heating and outcrop weathering. Discrete and macroscopic organic remains, macro and microfossils, magnetic grains, and sedimentary structures can be preferentially preserved within concretions. Here, Cretaceous carbonate concretions of the Holz Shale are shown to contain relatively high carbonate‐free total organic carbon (TOC) contents (up to ~18.5 wt%) compared to the surrounding host rock (with
ISSN:1472-4677
1472-4669
DOI:10.1111/gbi.12194