PALEOECOLOGY AND BIODIVERSITY OF PLIO-PLEISTOCENE MOLLUSK ASSEMBLAGES OF THE FLORIDA SHELL AND FILL QUARRY

The southeastern United States, particularly the state of Florida, possess a rich Cenozoic fossil record with abundant and well-preserved shelly faunas. This is exemplified well by the Florida Shell and Fill Quarry in Charlotte County, a site that possesses a relatively long stratigraphic section with a combined vertical exposure of twenty one meters. The exposed sequence of unlithified and partly lithified sediments encompasses geologic units ranging from the upper Pliocene Ochopee Member of the Tamiami Formation to the upper Pleistocene Fort Thompson Formation. These units represent a substantial interval of geological time (~ three million years). This study aims to investigate paleoecology of mollusk fossil assemblages from a new well-exposed quarry representing one of the critical time intervals (transition from Pliocene to Pleistocene) in the late Cenozoic history of coastal habitats of southeastern North America.

Field collection involved measuring four quarry sections to capture the entire twenty-one vertical meters exposed at the site. Sixty bulk samples were collected at twenty cm intervals across all four sections and assembled into a composite section of the quarry. Following field collection, the bulk samples were screen-washed, subsampled, and picked for gastropods and bivalves. Specimens were identified to species level whenever possible. The resulting data were explored using diversity measures, evenness measures, and multivariate ordinations to examine trends in biodiversity and faunal composition of mollusk assemblages. Dominant taxa included Chione erosa and Crassinella lunulata. Preliminary results suggest that standardized species richness declined upward throughout the sampled succession. Concurrently, faunal composition shifted gradually through time with stratigraphically adjacent samples being more similar in mollusk composition than those that were far apart vertically. The pattern of last occurrences of species appears gradual across the stratigraphic interval that could potentially record the Plio-Pleistocene extinction.