PLEISTOCENE MOLLUSCAN PALEOECOLOGY IN THE FLORIDA SHELL AND FILL QUARRY (FLORIDA, USA)

The Florida Shell and Fill Quarry near Punta Gorda in Charlotte County is a new ephemeral excavation that provides access to a relatively long stratigraphic section with a combined vertical exposure of 21 m. This long stratigraphic section offers an opportunity to advance our understanding of the Cenozoic fossil record of Florida. The geologic units exposed in the quarry range from the upper Pliocene Ochopee Member of the Tamiami Formation to the upper Pleistocene Fort Thompson Formation. This study focuses on the non-moldic, Pleistocene formations (from oldest to youngest - Caloosahatchee, Bermont, and Fort Thompson). These units contain an abundant and well-preserved molluscan fauna. Using high resolution bulk sampling, our survey documents spatial and temporal trends in diversity and faunal composition of mollusk assemblages and evaluates those trends in local environmental and stratigraphic contexts.

We collected 60 bulk samples at 20 cm intervals across four measured sections assembled into a composite section. Following field collection, the bulk samples were screen-washed to 2 mm and subsampled for gastropods and bivalves. Specimens were identified to species level whenever possible. The resulting data were explored using diversity measures and multivariate ordinations to examine trends in biodiversity and faunal composition of mollusk assemblages. In addition to these analyses, ecological information (e.g., salinity preference) were compiled for the closest living relatives of the top 20 most abundant mollusks. Based on the ecological preferences of the most abundant mollusks, as well as the sedimentological characteristics of the sampled units, the studied Pleistocene succession was interpreted as recording a potential environmental shift from low-energy coastal environments (e.g., lagoonal, or back sound settings) to high-energy shallow subtidal settings. The postulated environmental shift suggests that the studied Pleistocene succession records directional base-level changes that resulted in gradual deepening through time, which may have triggered corresponding lithological and faunal shifts.