23-15 Controls on Differential Fossil Preservation Across the K-Pg Boundary from Ephemeral Exposures of the Owl Creek and Clayton Formations Along Highway Construction in Northern Mississippi, USA

Session: Paleontology of North America (Posters)

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Abstract:

An ongoing state-supported construction project to widen the north-south oriented Mississippi (MS) State Highway 15 has produced a number of new exposures of the Cretaceous-Paleogene (K-Pg) boundary nearly along strike in Union and Tippah counties, MS. This provides a rare opportunity to investigate laterally extensive sedimentological and paleontological patterns throughout the duration of the roadwork. As new exposures were excavated, we performed fieldwork that involved measuring stratigraphic sections and collecting samples spanning the boundary, as well as collecting fossils from spoil piles of excavated material. Preliminary lab work involved fossil taphonomy, thin section analysis, and X-ray Diffraction (XRD) for mineralogy. The Owl Creek Formation is fossiliferous, glauconitic muddy micrite to micritic sandstone. Fossils preserved in the muddy micrite lithofacies show an abundance of original preservation in mollusks, however, sandier lithofacies are associated with dissolution of shell material, leaving only internal molds. A few mollusks with calcite original preservation remain. In the Clayton Formation, lithology ranges from allochemic sandstone, glauconitic sandstone, to limestone. Fossils were commonly found in the allochemic sandstone, glauconitic sandstone, and limestone lithofacies. Fossil preservation is variable in the allochemic sandstone. The allochem sandstone lenses are packed with fragmental fossils and some whole fossils. The preservation in these lenses shows goethite and sparry calcite pseudomorphs, quartz internal molds, and original preservation. The fossils in the glauconitic sandstone are mostly preserved as internal molds.  Variations of fossil preservation and lithology throughout the Owl Creek and Clayton Formations suggest grain size and permeability strongly influenced their diagenetic histories. The larger percentage of sand-sized particles likely allowed for greater circulation of diagenetic fluids and dissolution of aragonitic shells. The presence of sparry calcite and goethite pseudomorphs in the Clayton Formation suggests an early diagenetic calcite replacement followed later by a change in diagenetic pore fluids that facilitated replacement by goethite, but additional analyses and research are required to determine detailed diagenetic history.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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