QUANTIFYING TAPHONOMIC TRENDS AND BIASES IN LATE CENOZOIC COASTAL PLAIN DEPOSITS

The Coastal Plain deposits of the Eastern U.S. are mostly or entirely unlithified and therefore ideal for collecting quantitative, bulk-collected samples of well-preserved macro-invertebrate fossils. However, even in this ideal case, taphonomic biases may overprint spatial and temporal aspects of the fossil record, and should be evaluated rigorously prior to undertaking any paleobiological analyses. Moreover, the taphonomic trends throughout the Late Cenozoic fossil record have not been quantified for any region of the world, and their potential biasing importance is therefore not understood. This study assesses taphonomic trends in the Late Cenozoic Coastal Plain deposits by using specimen-based taphonomic scores. These scores are subjected to multivariate methods to quantify the scale and nature of taphonomic changes in this mollusk-dominated fossil record and evaluated for presence of spatial and/or temporal taphonomic biases. Bulk samples from the mid-Atlantic Coastal Plain of Maryland, Virginia, and adjacent areas, comprising >100 samples and >50,000 specimens, were used for this study. Stratigraphic intervals represented include the Yorktown (lower Pliocene), Eastover (upper Miocene) and St. Mary's (upper Miocene) formations. All samples were collected in bulk and subsequently sieved and specimens identified to the species level. Veneroid bivalves were selected for taphonomic analysis since they are common throughout the intervals selected for study, and also robust enough to be identified even when poorly preserved. A series of taphonomic variables quantifying biological, chemical, and physical aspects of shell alteration were recorded for each veneroid bivalve specimen. These data will be subjected to multivariate analysis in order to quantify large-scale spatial and temporal taphonomic patterns in the Late Cenozoic fossil record of the mid-Atlantic Coastal Plain.