LATE CENOZOIC MOLLUSCAN DIVERSITY AND ECOLOGY: PATTERNS FROM THE FOSSIL RECORD OF VIRGINIA

Unconsolidated deposits of the Atlantic Coastal Plain provide exceptional opportunities for field-based quantitative investigations of the Cenozoic fossil record of mollusks. These relatively complete and highly fossiliferous time sequences preserve rich biological information for studying long-term changes in biodiversity in the context of a substantial global climate change. In this study we compare diversity and ecology of the Upper Miocene Cobham Bay Member of the Eastover Formation and Lower Pliocene Sunken Meadow member of the Yorktown Formation, sedimentary units that are believed to correspond to a notable climatic shift from the culmination of a cooling event to the subsequent warming and sea level transgression. We utilize two types of data, bulk field collected samples and preexisting museum samples. This approach allowed us not only to acquire multiple proxies of the analyzed secular diversity patterns, but also to compare and contrast diversity proxies provided by different types of data. Ordination of the data (DCA) suggests that a gradual change occurs in taxonomic composition of the two studied units across the unconformable Miocene/Pliocene boundary. Preliminary data suggest that bulk field collections and museum data provide similar reconstructions of taxonomic composition, diversity and ecology trends over time, even though they were significantly different in terms of apparent taphonomic preservation. Museum samples examined thus far appear to offer good fidelity to field bulk samples, and bulk collected field data were not distinguishable from Museum data via rarefaction, ordination or cross-validation techniques. The preliminary results provide a compelling empirical example of the impact of data collecting methods on the nature of retrieved secular patterns.