PROVINCIALITY OF LATE PLEISTOCENE MOLLUSCS OF VIRGINIA AND NORTHERN NORTH CAROLINA: A TEST CASE FOR COMPARING POPULATION ANALYSES AT THE GENUS AND SPECIES LEVELS

Recent continental shelf molluscs from New England to Florida can define cold-temperate (Boreal), temperate (Virginian), warm-temperate (transitional, Kitty Hawk to Cape Hatteras) and subtropical (Carolinian, south of Cape Hatteras) provinces. The Virginian fauna further separates into three sub-assemblages, divided at New Jersey and Maryland. Projecting these thermal regimes through time by species richness was limited by extinction typically exceeding 80 % in Pliocene molluscs. With 5 % extinction of Pliocene genera, genus-level comparisons were more inclusive but not necessarily comparable. We developed a quantified approach of genera richness for analyzing provinciality and interpreting Atlantic Coastal Plain molluscan assemblages. Testing our model using Late Pleistocene faunas [less than 2% species extinction] enabled species-level and genus-level comparisons.

We compared Late Pleistocene molluscan species assemblages from eastern Virginia and North Carolina with Recent faunal provinces. Differences between fossil and Recent population patterns were calculated by determining equivalent points in nine-dimensional hyperspace. The resulting provinciality of Virginia Pleistocene formations, oldest to youngest is: Great Bridge, temperate to warm-temperate; Lower Norfolk, warm-temperate; Upper Norfolk, temperate to warm-temperate; Lower Kempsville, temperate to warm-temperate; Upper Kempsville, temperate; Londonbridge, temperate; Lower Sandbridge, temperate; and Upper Sandbridge, temperate to warm-temperate. North Carolina Pleistocene Flanner Beach Formation assemblages strongly conform with the Recent warm-temperate biota. None of the documented assemblages approached sub-tropical patterns. These analyses with Pleistocene assemblages supported our genus-richness model, only differing slightly where calculated values indicated almost equal affinity for temperate or warm-temperate interpretation.

Most of these Virginia strata were deposited during the Sangamon when sea levels were as much as 10 to 15 meters higher than present. These Pleistocene faunas indicate that inter-glacial sea level maxima may occur without major shifts in marine provinciality.