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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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| Published in: | Geobiology 2017-01, Vol.15 (1), p.146-157 |
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| creator | Loyd, S. J. |
| description | 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 |
| doi_str_mv | 10.1111/gbi.12194 |
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J.</creator><creatorcontrib>Loyd, S. J.</creatorcontrib><description>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 <2.1 wt%). TOC increases with total inorganic carbon (TIC) content, a metric of the degree of cementation. Pyrite contents within concretions generally correlate with organic carbon contents. Concretion carbonate carbon isotope compositions (δ13Ccarb) range from −22.5 to −3.4‰ (VPDB) and do not correlate strongly with TOC. Organic carbon isotope compositions (δ13Corg) of concretions and host rock are similar. Thermal maturity data indicate that both host and concretion organic matter are overmature and have evolved beyond the oil window maturity stage. Although the organic matter in general has experienced significant oxidative weathering, concretion interiors exhibit lower oxygen indices relative to the host. These results suggest that carbonate concretions can preferentially preserve overmature, ancient, sedimentary organic matter during outcrop weathering, despite evidence for organic matter degradation genetic mechanisms. As a result, concretions may provide an optimal proxy target for characterization of more primary organic carbon concentrations and chemical compositions. In addition, these findings indicate that concretions can promote delayed oxidative weathering of organic carbon in outcrop and therefore impact local chemical cycling.</description><identifier>ISSN: 1472-4677</identifier><identifier>EISSN: 1472-4669</identifier><identifier>DOI: 10.1111/gbi.12194</identifier><identifier>PMID: 27384615</identifier><language>eng</language><publisher>England: Wiley Subscription Services, Inc</publisher><subject>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</subject><ispartof>Geobiology, 2017-01, Vol.15 (1), p.146-157</ispartof><rights>2016 John Wiley & Sons Ltd</rights><rights>2016 John Wiley & Sons Ltd.</rights><rights>Copyright © 2017 John Wiley & Sons Ltd</rights><lds50>peer_reviewed</lds50><woscitedreferencessubscribed>false</woscitedreferencessubscribed><citedby>FETCH-LOGICAL-c4804-13bbcb7988f86e6ee1d83abaacc32c7b6d031414f27ef2a0cd689b0d7ebae9063</citedby><cites>FETCH-LOGICAL-c4804-13bbcb7988f86e6ee1d83abaacc32c7b6d031414f27ef2a0cd689b0d7ebae9063</cites></display><links><openurl>$$Topenurl_article</openurl><openurlfulltext>$$Topenurlfull_article</openurlfulltext><thumbnail>$$Tsyndetics_thumb_exl</thumbnail><link.rule.ids>314,776,780,27901,27902</link.rule.ids><backlink>$$Uhttps://www.ncbi.nlm.nih.gov/pubmed/27384615$$D View this record in MEDLINE/PubMed$$Hfree_for_read</backlink></links><search><creatorcontrib>Loyd, S. J.</creatorcontrib><title>Preservation of overmature, ancient, sedimentary organic matter in carbonate concretions during outcrop weathering</title><title>Geobiology</title><addtitle>Geobiology</addtitle><description>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 <2.1 wt%). TOC increases with total inorganic carbon (TIC) content, a metric of the degree of cementation. Pyrite contents within concretions generally correlate with organic carbon contents. Concretion carbonate carbon isotope compositions (δ13Ccarb) range from −22.5 to −3.4‰ (VPDB) and do not correlate strongly with TOC. Organic carbon isotope compositions (δ13Corg) of concretions and host rock are similar. Thermal maturity data indicate that both host and concretion organic matter are overmature and have evolved beyond the oil window maturity stage. Although the organic matter in general has experienced significant oxidative weathering, concretion interiors exhibit lower oxygen indices relative to the host. These results suggest that carbonate concretions can preferentially preserve overmature, ancient, sedimentary organic matter during outcrop weathering, despite evidence for organic matter degradation genetic mechanisms. As a result, concretions may provide an optimal proxy target for characterization of more primary organic carbon concentrations and chemical compositions. In addition, these findings indicate that concretions can promote delayed oxidative weathering of organic carbon in outcrop and therefore impact local chemical cycling.</description><subject>Carbon</subject><subject>Carbon Isotopes - analysis</subject><subject>Carbonates - analysis</subject><subject>Concretions</subject><subject>Geologic Sediments - chemistry</subject><subject>Inorganic carbon</subject><subject>Isotopes</subject><subject>Membrane permeability</subject><subject>Minerals</subject><subject>Organic Chemicals - analysis</subject><subject>Organic compounds</subject><subject>Organic matter</subject><subject>Preservation</subject><subject>Pyrite</subject><subject>Sediments</subject><subject>Shale</subject><subject>Total organic carbon</subject><subject>Weathering</subject><issn>1472-4677</issn><issn>1472-4669</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2017</creationdate><recordtype>article</recordtype><recordid>eNqNkU1LHTEUhkOp1I924R8ogW4UvJqTyU0yy1b8AsEu2nVIMmeukTvJbTKj-O_N9aqLQotZJIfw8BzOeQnZB3YM9ZwsXDgGDq34QHZAKD4TUrYf32qltsluKXeMcTFv4BPZ5qrRQsJ8h-SfGQvmezuGFGnqabrHPNhxynhEbfQB43hEC3ZhqJXNjzTlhY3B0wqNmGmI1NvsUrQjUp-iz7hWFdpNOcQFTdPoc1rRB7TjLa6_PpOt3i4Lfnl598jv87Nfp5ez65uLq9Pv1zMvNBMzaJzzTrVa91qiRIRON9ZZ633DvXKyYw0IED1X2HPLfCd161in0FlsmWz2yMHGu8rpz4RlNEMoHpdLGzFNxYCet0JBvd6BcqkAFF9bv_2F3qUpxzqI4cDmtW8j2P8o0EKrVjCASh1uqLqhUjL2ZpXDUJdsgJl1sqYma56TrezXF-PkBuzeyNcoK3CyAR7CEh__bTIXP642yick363n</recordid><startdate>201701</startdate><enddate>201701</enddate><creator>Loyd, S. J.</creator><general>Wiley Subscription Services, Inc</general><scope>CGR</scope><scope>CUY</scope><scope>CVF</scope><scope>ECM</scope><scope>EIF</scope><scope>NPM</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>8FD</scope><scope>F1W</scope><scope>FR3</scope><scope>H95</scope><scope>L.G</scope><scope>P64</scope><scope>RC3</scope><scope>7X8</scope></search><sort><creationdate>201701</creationdate><title>Preservation of overmature, ancient, sedimentary organic matter in carbonate concretions during outcrop weathering</title><author>Loyd, S. J.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c4804-13bbcb7988f86e6ee1d83abaacc32c7b6d031414f27ef2a0cd689b0d7ebae9063</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2017</creationdate><topic>Carbon</topic><topic>Carbon Isotopes - analysis</topic><topic>Carbonates - analysis</topic><topic>Concretions</topic><topic>Geologic Sediments - chemistry</topic><topic>Inorganic carbon</topic><topic>Isotopes</topic><topic>Membrane permeability</topic><topic>Minerals</topic><topic>Organic Chemicals - analysis</topic><topic>Organic compounds</topic><topic>Organic matter</topic><topic>Preservation</topic><topic>Pyrite</topic><topic>Sediments</topic><topic>Shale</topic><topic>Total organic carbon</topic><topic>Weathering</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Loyd, S. J.</creatorcontrib><collection>Medline</collection><collection>MEDLINE</collection><collection>MEDLINE (Ovid)</collection><collection>MEDLINE</collection><collection>MEDLINE</collection><collection>PubMed</collection><collection>CrossRef</collection><collection>Technology Research Database</collection><collection>ASFA: Aquatic Sciences and Fisheries Abstracts</collection><collection>Engineering Research Database</collection><collection>Aquatic Science & Fisheries Abstracts (ASFA) 1: Biological Sciences & Living Resources</collection><collection>Aquatic Science & Fisheries Abstracts (ASFA) Professional</collection><collection>Biotechnology and BioEngineering Abstracts</collection><collection>Genetics Abstracts</collection><collection>MEDLINE - Academic</collection><jtitle>Geobiology</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Loyd, S. J.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Preservation of overmature, ancient, sedimentary organic matter in carbonate concretions during outcrop weathering</atitle><jtitle>Geobiology</jtitle><addtitle>Geobiology</addtitle><date>2017-01</date><risdate>2017</risdate><volume>15</volume><issue>1</issue><spage>146</spage><epage>157</epage><pages>146-157</pages><issn>1472-4677</issn><eissn>1472-4669</eissn><abstract>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 <2.1 wt%). TOC increases with total inorganic carbon (TIC) content, a metric of the degree of cementation. Pyrite contents within concretions generally correlate with organic carbon contents. Concretion carbonate carbon isotope compositions (δ13Ccarb) range from −22.5 to −3.4‰ (VPDB) and do not correlate strongly with TOC. Organic carbon isotope compositions (δ13Corg) of concretions and host rock are similar. Thermal maturity data indicate that both host and concretion organic matter are overmature and have evolved beyond the oil window maturity stage. Although the organic matter in general has experienced significant oxidative weathering, concretion interiors exhibit lower oxygen indices relative to the host. These results suggest that carbonate concretions can preferentially preserve overmature, ancient, sedimentary organic matter during outcrop weathering, despite evidence for organic matter degradation genetic mechanisms. As a result, concretions may provide an optimal proxy target for characterization of more primary organic carbon concentrations and chemical compositions. In addition, these findings indicate that concretions can promote delayed oxidative weathering of organic carbon in outcrop and therefore impact local chemical cycling.</abstract><cop>England</cop><pub>Wiley Subscription Services, Inc</pub><pmid>27384615</pmid><doi>10.1111/gbi.12194</doi><tpages>12</tpages></addata></record> |
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| 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 |
| title | Preservation of overmature, ancient, sedimentary organic matter in carbonate concretions during outcrop weathering |
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