Sea level, carbonate mineralogy, and early diagenesis controlled δ13C records in Upper Ordovician carbonate

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dc.contributor.authorJones, David S.
dc.contributor.authorBrothers, R. William
dc.contributor.authorAhm, Anne-Sofie
dc.contributor.authorSlater, Nicholas
dc.contributor.authorHiggins, John A.
dc.contributor.authorFike, David A.
dc.date.accessioned2026-07-09T20:20:49Z
dc.date.available2026-07-09T20:20:49Z
dc.date.issued2019
dc.description.abstractStratigraphic variability in the geochemistry of sedimentary rocks provides critical data for interpreting paleoenvironmental change throughout Earth history. However, the vast majority of pre-Jurassic geochemical records derive from shallow-water carbonate platforms that may not reflect global ocean chemistry. Here, we used calcium isotope ratios (δ44Ca) in conjunction with minor-element geochemistry (Sr/Ca) and field observations to explore the links among sea-level change, carbonate mineralogy, and marine diagenesis and the expression of a globally documented interval of elevated carbon isotope ratios (δ13C; Hirnantian isotopic carbon excursion [HICE]) associated with glaciation in Upper Ordovician shallow-water carbonate strata from Anticosti Island, Canada, and the Great Basin, Nevada and Utah, USA. The HICE on Anticosti is preserved in limestones with low δ44Ca and high Sr/Ca, consistent with aragonite as a major component of primary mineralogy. Great Basin strata are characterized by lateral gradients in δ44Ca and δ13C that reflect variations in the extent of early marine diagenesis across the platform. In deep-ramp settings, deposition during synglacial sea-level lowstand and subsequent postglacial flooding increased the preservation of an aragonitic signature with elevated δ13C produced in shallow-water environments. In contrast, on the mid- and inner ramp, extensive early marine diagenesis under seawater-buffered conditions muted the magnitude of the shift in δ13C. The processes documented here provide an alternative explanation for variability in a range of geochemical proxies preserved in shallow-water carbonates at other times in Earth history, and challenge the notion that these proxies necessarily record changes in the global ocean.
dc.description.reviewstatusReviewed
dc.description.scholarlevelFaculty
dc.description.sponsorshipJones acknowledges the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. Ahm acknowledges support from the Simons Foundation (New York, SCOL 611878).
dc.identifier.citationJones, D. S., Brothers, R. W., Ahm, A.-S. C., Slater, N., Higgins, J. A., & Fike, D. A. (2020). Sea level, carbonate mineralogy, and early diagenesis controlled δ13C records in Upper Ordovician carbonates. Geology (Boulder), 48(2), 194–199. https://doi.org/10.1130/G46861.1
dc.identifier.urihttps://doi.org/10.1130/G46861.1
dc.identifier.urihttps://hdl.handle.net/1828/24063
dc.language.isoen
dc.publisherGeology
dc.rightsCC-BY
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/
dc.subject.departmentSchool of Earth and Ocean Sciences
dc.titleSea level, carbonate mineralogy, and early diagenesis controlled δ13C records in Upper Ordovician carbonate
dc.typeArticle

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