MOLLUSCAN ASSEMBLAGES AND SEDIMENTOLOGY OF THE PALEOCENE AQUIA FORMATION AT TINKERS CREEK IN PRINCE GEORGE’S COUNTY, MARYLAND

Outcrops from the Tinkers Creek in Maryland expose a long and heavily fossiliferous stretch of the Paleocene-aged Aquia Formation, providing an opportunity to study patterns of molluscan recovery following the end-Cretaceous mass extinction. Previous research focusing on these outcrops has provided a detailed framework of sedimentology and biostratigraphy, making it possible to assess how molluscan paleoecology varies both spatially and through time within the locality. Aquia Formation sediments along Tinkers Creek include layers of burrowed silty-sand composed of quartz, glauconite, and mica, alternating with two indurated beds of calcite-cemented wackestone protruding out of the bank.

The overarching goal of this research was to assess how molluscan taxon composition, richness, diversity, abundance, and community structure vary by sedimentology, with emphasis placed on lateral and vertical changes across the outcrops. An additional objective was determining whether there are differences in grain size and lithology across the layers. Surficial and at depth samples were taken of fossils and sedimentology for a total of 26 quadrats, representing approximately 6 meters of horizontal section over 0.7 km of distance. Sediment descriptions were compiled for each quadrat while 10 samples from the indurated beds and adjacent deposits were collected for thin-section analysis.

A total of 2,234 specimens, representing 10 identifiable species, were sampled overall. The gastropod species Kapalmerella mortoni and K. humerosa make up the majority of identifiable specimens in most quadrats. The bivalves Panopea elongata and Venericardia regia are strictly limited to the indurated layers but are abundant within them. Preliminary results suggest that taxon richness, rarefied to 11 specimens, ranges from 1.97 to 4.11 species and does not vary significantly by facies.