FUNCTIONAL ECOLOGY OF MARINE INVERTEBRATES ACROSS THE END-CRETACEOUS FROM A NEW SHALLOW SHELF KPG BOUNDARY SITE IN NORTHERN MISSISSIPPI

The Ellis Sand Pit of northern Mississippi represents a previously undescribed Cretaceous-Paleogene boundary (KPB) section from the U.S. Gulf Coastal Plain. Ellis Sand Pit is located in the Mississippi Embayment, ~1,400 km north of the Chicxulub impact site and preserves a spherule rich KPB event bed and fossil-rich Danian strata that provide a more complete stratigraphic record of the pre- and post- extinction conditions compared to the well-studied late Maastrichtian Owl Creek type section 24 km to the north. We report paleotemperature reconstruction, taphonomy, diversity, functional ecology, and body size of shallow marine invertebrates from the late Maastrichtian and early Danian.

The stratigraphic section includes 1m of the upper Owl Creek Fm which is composed of a fine- to medium-grained sand with a clay matrix and preserves original shell material. The 10-15cm thick spherule layer is a heavily oxidized medium to coarse quartz sand with clay-replacement of siliceous spherules and calcareous fossils. The 1m thick Danian Clayton Fm exposure consists of a fossiliferous sandy limestone. Species diversity metrics, body size, and functional ecology were used to assess ecosystem change across the KPB in the context of potential taphonomic biases.

Δ47-based paleotemperature reconstructions from n=26 shells across the KPB indicate seawater temperatures at this site were 22.3°C +/- 3.3° with no directional change throughout the section or shift across the KPB. The spherule layer is composed of reworked Cretaceous fauna but has higher taxonomic and functional ecological diversity and smaller body size than the Owl Creek Fm. The spherule layer contains more carnivores, epifaunal, and actively motile taxa and fewer deep infauna and facultatively mobile taxa. Differences in size, diversity, and ecology between fauna in the Owl Creek Fm and spherule layer are likely a taphonomic bias as morphologic details are better preserved in clay replaced fossils, thus more species were identified. The Clayton limestone is rich in an overall less mobile, more epifaunal and suspension feeding fauna of oysters, turritellids, and bryozoans suggesting an ecosystem shift across the KPB into the Danian recovery. Continued study will inform comparisons to Danian bryozoan mounds described from Europe.