Carbon isotope trends of Precambrian-Cambrian carbonates in southwestern Laurentia are robust to diagenetic overprinting

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dc.contributor.authorLonsdale, Mary C.
dc.contributor.authorAhm, Anne-Sofie C.
dc.contributor.authorNelson, Lyle L.
dc.contributor.authorThompson, Jacob W.
dc.contributor.authorHiggins, John A.
dc.contributor.authorSmith, Emily F.
dc.date.accessioned2026-07-09T20:20:46Z
dc.date.available2026-07-09T20:20:46Z
dc.date.issued2026
dc.description.abstractAn extreme negative (<-6‰) carbon isotope (δ13C) excursion is recognized globally in strata recording the Ediacaran-Cambrian boundary. This excursion has been termed the BAsal Cambrian carbon isotope Excursion (BACE). It, like other carbon isotope excursions throughout the geologic record, has been interpreted to record a perturbation to the global carbon cycle based on the assumption that shallow water carbonate sediments and rock preserve an accurate time-series of the ?13C composition of the global ocean. However, this assumption has been demonstrated to be inaccurate in some shallow water settings; pervasive early diagenetic alteration of shallow water carbonate δ13C records and local carbon cycling within the platform environment can result in the decoupling of global ocean and shallow water carbonate δ13C values. Here, we test the extent and isotopic effects of early diagenetic alteration of shallow water carbonate sediments that record the BACE in southwestern Laurentia using carbonate stable isotope (δ13C, δ18O, δ44/40Ca, δ26Mg) and major and minor element (Mg/Ca, Sr/Ca) geochemistry. The δ44/40Ca values of the three studied sections are consistent with different modes of diagenetic alteration, ranging from more sediment-buffered to more fluid-buffered early marine diagenesis. Dolostone δ26Mg and δ18O values suggest that diagenetic alteration and dolomitization occurred prior to significant burial. Because the δ13C chemostratigraphic records are reproducible despite the variable diagenetic regimes among the three sites, we argue that the prominent δ13C stratigraphic trends were insensitive to diagenetic overprinting and instead reflect changes in the primary δ13C composition of dissolved inorganic carbon of platform seawater. Finally, we explore a potential link between the BACE, an increase in early marine fluid-buffered marine diagenesis of platform carbonates, and magmatism associated with the rifting of the southwest margin of Rodinia.
dc.description.reviewstatusReviewed
dc.description.scholarlevelFaculty
dc.description.sponsorshipEFS acknowledges support from the National Science Foundation (NSF EAR-1827669 and NSF EAR-2021064), the Sloan Research Fellowship (#FG-2021-16049), and the Johns Hopkins Catalyst Award.
dc.identifier.citationLonsdale, M. C., Ahm, A.-S. C., Nelson, L. L., Thompson, J. W., Higgins, J. A., & Smith, E. F. (2026). Carbon isotope trends of Precambrian-Cambrian carbonates in southwestern Laurentia are robust to diagenetic overprinting. American Journal of Science (1880), 326, 1. https://doi.org/10.2475/001c.155346
dc.identifier.urihttps://doi.org/10.2475/001c.155346
dc.identifier.urihttps://hdl.handle.net/1828/24062
dc.language.isoen
dc.publisherAmerican Journal of Science
dc.rightsCC-BY
dc.rights.urihttps://creativecommons.org/licenses/by/4.0
dc.subjectsouthern Great Basin
dc.subjectmarine diagenesis
dc.subjectcarbonate geochemisty
dc.subjectEdiacaran-Cambrian boundary
dc.subjectcalcium isotopes
dc.subject.departmentSchool of Earth and Ocean Sciences
dc.titleCarbon isotope trends of Precambrian-Cambrian carbonates in southwestern Laurentia are robust to diagenetic overprinting
dc.typeArticle

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