COMMUNITY ANALYSIS OF THE BIVALVES IN THE EARLY PLEISTOCENE BERMONT FORMATION

In Florida, little detailed stratigraphic work has been published on the Pleistocene fossil shell beds. This study examines the bivalve fauna of the early Pleistocene Bermont “Formation”, at the assemblage-level to determine if individual beds record single communities (biocoenoses) or mixtures of different communities (thanatocoenoses), and to help determine if the same environments recur through time. Five distinct stratigraphic horizons (denoted as 2C, 3C, 4C, 5C, and 6B) within the Longan Lakes quarry in Collier County, Florida were bulk sampled, sieved, and sorted to determine the taxonomy and abundance of all bivalve taxa present. The highest species richness (n = 55) was recorded in 4C, whereas in the other samples it ranged from 49 to 33 bivalve taxa. In all samples, the most abundant species present was Chione elevata. 4C had a greater abundance of oysters and the mussel Brachiodontes exustus than the other samples. Overall the samples remained fairly similar. The ten most abundant species in this study were (in order): Chione elevata (approximately 5000 individuals), Transenella cubaniana (approximately 1800 individuals), Lucina multilineata (465 individuals), Lucina floridana, Ostrea sp., Pteria colymbus, Lucina nassula, Carditamera floridana, Divaricella quadrisulcata, and Brachiodontes exustus. The last seven species listed had numbers in the range of 150 to 350. In the case of Chione elevata and Transenella cubaniana all samples showed high abundance. Lucina multilineata, Pteria colymbus, Lucina nassula, and Brachiodontes exustus all had the highest abundance in 4C. Lucina floridana, Divaricella quadrisulcata and Ostrea sp. all had the highest abundance in 3C. Carditamera floridana was most abundant in 2C. Species that were found in only one or two samples were generally very low in abundance. The similarity among the horizons indicates that there was some recurrence in the environments through time, with the environment recorded in 4C being the most different among them.