TEN YEARS OF PICKING SHELLS: FAUNAL PATTERNS IN THE NEOGENE ATLANTIC COASTAL PLAIN DEPOSITS OF VIRGINIA

Bulk field samples from unconsolidated Neogene deposits of the Atlantic Coastal Plain have provided vast quantities of fossil material for paleontological investigations. Over the past decade, 77,669 bivalve specimens were collected via bulk sampling in the Salisbury Embayment of southeastern Virginia. The samples range in age from upper Miocene (Cobham Bay Member of the Eastover Formation) through the Pliocene (Sunken Meadow (lower Pliocene), Rushmere (upper Pliocene) and Morgart's Beach (upper Pliocene) members of the Yorktown Formation). These sedimentary units are unconsolidated and highly fossiliferous, forming a stratigraphic sequence representing approximately 5 million years of time. The sequence records a climatic shift from the end of a cooling event through subsequent warming and sea level transgression. Multivariate statistical analysis techniques, including Detrended Correspondence Analysis (DCA), which has shown to be useful for extracting simple paleoenvironmental gradients, were used to explore faunal relationships among the 85 most abundant genera included in the 235 bulk samples. DCA axes, when plotted against stratigraphic level, revealed variation in the data that was likely produced by bathymetric and/or water energy level changes over time based on comparison with preliminary sedimentological and paleoecological data. The usefulness of DCA in analyzing faunal data will be discussed.