129-31 Geochemical and Isotopic Analysis of the Late Cretaceous Coon Creek Formation using Inoceramid Bivalves and Sediment Minerology

Abstract:

An exceptional outcrop of the Coon Creek Formation, located in McNairy County, Tennessee, is a Late Cretaceous (76 Ma) Lagerstätte that contains abundant invertebrates, plant remains, and vertebrates (mosasaurs, plesiosaurs, and sharks). Whereas the deposits are part of the Mississippi Embayment, and marine in origin, there have been questions about how far from the shoreline and how deep the ocean was at the location during the time of sediment deposition. Although mosasaurs existed across a range of temperatures, previous workers have noted their occurrence in strata where temperatures were colder. The Coon Creek locality is an ideal site for reconstructing paleotemperature because previous workers have inferred no diagenetic alteration of the fossil material. Here, we present mineralogical and elemental geochemical data for sediments across the site as well as stable isotopic geochemistry data from exceptionally preserved inoceramid bivalves. Mineralogy shows little variation across the locality, suggesting uniform depositional conditions. Elemental geochemistry was used to reconstruct pH, and carbonate δ¹⁸O values of inoceramids found proximal to the mosasaur excavations were used to reconstruct the paleotemperature of the site. These paleotemperature estimates are compared with those from other locations that contain both inoceramids and mosasaurs (such as Bentiaba in Angola) to discuss potential variability in mosasaur habitats. 

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