PALEOECOLOGY OF THE WACCAMAW FORMATION (PLIO-PLEISTOCENE) NEAR OLD DOCK, COLUMBUS COUNTY, NORTH CAROLINA

A paleoecological analysis was conducted for a molluscan assemblage from a previously undescribed locality of the Plio-Pleistocene Waccamaw Formation near Old Dock, Columbus County, North Carolina. The assemblage is time averaged but exhibits a high taphonomic grade, based on percent articulation determined from field observations and percent breakage and corrasion assessed in the laboratory. A bulk sample was wet sieved and whole specimens, bivalve beaks, and gastropod apices >1 mm were picked. Approximately 4,000 specimens representing 40 bivalve and 37 gastropod species were counted and identified. The assemblage exhibits a high species richness, Shannon diversity index, and evenness; values resemble those tabulated for a similar sample from the partially correlative James City Formation from the Lee Creek Mine, North Carolina. The Old Dock bivalve fauna is dominated by suspension feeders; most species have siphonate infaunal or nonsiphonate infaunal life modes. The gastropod fauna has a high representation of carnivores as well as suspension feeders. Trophic and life mode structure is similar to that of the modern fauna off the North Carolina coast, although the Old Dock assemblage has a more tropical aspect and exhibits higher diversity. Intensity of drilling gastropod predation was calculated as percent of individuals with one or more drill holes. Holes drilled by naticid and muricid gastropods were not tallied separately because they are difficult to distinguish in thin-shelled prey; however, most holes were probably naticid in origin, based on the relative abundance of naticids in the fauna. Approximately 15% of bivalve and 7% of gastropod individuals were drilled, yielding a value for the molluscan fauna of 12%. Other Waccamaw localities studied previously yielded naticid drilling intensities of 10 - 18% (12 - 23% for bivalves and 5 - 9% for gastropods); the correlative James City was drilled ~12%. Overall drilling for the Waccamaw/James City interval was ~12%, which is significantly less than that determined for the extant North Carolina mollusc fauna (21%). The increase in drilling in the Recent may be linked to recovery of the fauna from the Plio-Pleistocene extinctions or to climatic changes since the early Pleistocene.