INFERRING PLIO-PLEISTOCENE PALEOENVIRONMENTS IN SOUTHEASTERN NORTH CAROLINA USING OSTRACODA

As part of a three year Research Experiences for Undergraduates program at UNC Wilmington, molluscan fossil assemblages have been examined from multiple localities in the Carolinas to better understand Plio-Pleistocene regional faunal extinctions. Paleoenvironments must be well constrained when comparing paleocommunities; paleoecological analysis of microfossils can be used for this objective. Although our paleoenvironmental interpretations are derived from study of both Ostracoda and Foraminifera, results presented here are restricted to ostracods.

Microfossils were processed from six bulk samples collected at five NC localities. Pliocene samples are represented by the Duplin Formation at Tar Heel and on the Lumber River near Lumberton. Pleistocene samples were acquired from the lower Waccamaw Formation at Acme, Holloman Pit in Whiteville, and two distinct fossiliferous beds at Register Quarry near Old Dock. At least 300 ostracods were picked from each sample. Thus far, >75% of the ostracods in each sample have been identified to genus and work is still in progress.

To date, 21 genera have been documented across all samples. Eleven genera occur in every sample (Aurila, Bensonocythere, Cytherura, Haplocytheridea, Loxoconcha, Muellerina, Orionina, Paracytheridea, Pontocythere, Puriana, and Shattuckocythere) and constitute ~60%–80% of each assemblage. The dominant genus in five of the six samples is Aurila: Tar Heel (~29%), Acme (~19%), Holloman Pit (~19%), and Register Bed 1 (~25%) and Bed 2 (~31%). Pontocythere (~16%) is slightly more abundant than Aurila (~15%) at Lumber River and is the second most abundant taxon at Tar Heel (~19%), Holloman Pit (~12%), and Register Bed 1 (~16%) and Bed 2 (~12%). Pontocythere is third in abundance at Acme (~9%) behind Mutilus (~18%). Mutilus is common at Lumber River (~4%), Holloman Pit (~7%), and Register Bed 1 (~4%) and Bed 2 (~5%), but absent at Tar Heel.

Based on published literature (e.g., Howard 1974, Swain 1968), assemblages characterized by Pontocythere ashermani and Aurila conradi indicate warm, normal marine, inner to middle shelf environments. Co-occurrence of Mutilus confragosa further implies shallow, sublittoral marine conditions (Swain 1974). Similarity of habitats across these samples confirms their molluscan faunas can be compared with confidence.