AN OSTRACODE FAUNA FROM THE CLAYTON FORMATION (PALEOCENE) AND ANALYSIS OF SAMPLE-STANDARDIZED DIVERSITIES ACROSS THE K/PG BOUNDARY IN THE US COASTAL PLAIN

Despite their abundance, ostracode distributions are incompletely known in the U. S. Gulf Coastal Plain. Furthermore, there are few studies of their occurrence and turnover across the Cretaceous/Paleogene boundary. Here we document an ostracode fauna from the Paleocene (Danian) Pine Barren Member of the Clayton Formation, which immediately overlies the K/Pg boundary in central Alabama. Through this survey, we contribute to the knowledge of ostracode composition and diversity immediately following the K/Pg mass extinction.

The analyzed sample was collected from an exposure of the Pine Barren Member (31 59.1 N, 87 5.9 W). After collection, the sample was washed then wet-sieved to 100 microns, dried, and picked for ostracodes. Once picked, ostracodes were identified to the species level using standard taxonomic features, comparison to published works, and type specimens at the Natural Museum of Natural History. For occurrence data, individual valves were counted as one individual, whereas carapaces were counted as two individuals. In total, 339 individuals from 11 genera and 18 species were identified, some of which had never previously been reported from the Pine Barren Member, including Haplocytheridea leei, Vestustocytheridea fornicata, and Hermanites bassleri. SEM images were taken for species previously unreported.

We used classical rarefaction to assess sample-standardized alpha diversity in this sample and in previously published faunal data from the Pine Barren Member and the underlying upper Maastrichtian Prairie Bluff Chalk. These analyses were performed in order to analyze changes in species diversity across the K/Pg boundary. Rarefied diversity in our sample is similar to others from the Pine Barren Member, but markedly lower than late Cretaceous samples, reflecting a drop in alpha diversity following the extinction event. This diversity drop is also apparent, albeit more subdued, in published data from similar-aged formations in Maryland (the Maastrichtian Severn and Danian Brightseat Formations).