ABUNDANCE AND PALEOECOLOGY OF GASTROPODS IN THE SUNKEN MEADOW MEMBER, YORKTOWN FORMATION (PLIOCENE) OF SOUTHEASTERN VIRGINIA

Recent work on end-Cretaceous bivalves from the North American Coastal Plain suggests that abundant taxa are no more likely to survive mass extinctions than rare ones. This raises the question of whether a link exists between abundance and survivorship during background intervals in the fossil record. The purpose of this study is: (1) to document the abundance and evenness of gastropod communities in the Sunken Meadow Member of the Yorktown Formation in southeastern Virginia, (2) to determine the extent to which gastropod abundance varies spatially and temporally within this unit, and (3) to explore whether a correlation exists between gastropod abundance and survivorship within this unit. Eighteen bulk samples were collected from localities along the James River in southeastern Virginia. Bulk sample size was standardized according to dry weight and sieved using a 1mm mesh size. Gastropods were identified to species level and apices were counted to determine the number of individuals per species per sample. Abundance was quantified using raw, rank, and proportional metrics and the Simpson index, Shannon-Wiener index, and Pielou’s J’ were used to quantify diversity and evenness. Geological durations (i.e., stratigraphic ranges) were compiled for each species from the literature and used as a proxy for survivorship. The relationship between abundance and duration was assessed to explore the link between abundance and extinction during this interval. Spatiotemporal variability in abundance was also quantified and compared to survivorship. These field data, which are preliminary and restricted both spatially and temporally, were supplemented with literature data collected using similar sampling methods.