STRATIGRAPHY AND EVOLUTION OF A NORTHEASTERN SOUTH CAROLINA BARRIER SYSTEM: DEBORDIEU ISLAND

This study examines the evolution of DeBordieu Island as part of a larger, on-going USGS-SC Sea Grant Coastal Erosion Cooperative studying the northeastern South Carolina Grand Strand coastline. In order to determine the island’s architecture and sediment accumulation, ground penetrating radar profiles have been collected using a GSSI system with 200 MHz antennae in tandem with RTK GPS to correct for elevation. To ground-truth this data, a series of vibracores along transects have been collected. These cores were split and described for color, texture, and biologic components and selected subsamples were analyzed for grain size and organic content. Environments identified in the northern transect of four cores include modern transgressive beach, dune, overwash and a thin (0.5 m) landward marsh overlying pre-transgressive freshwater marsh, paleo-shoreface and paleo-paralic environments. A lower paleo-shoreface deposit containing carbonate nodules is mapped as a shallow point reflector surface extending landward of the central portion of the modern marsh system. Under the modern dune system, the freshwater marsh/upper humate cemented paleo-shoreface produces an intermittent strong reflector paralleling the coast. Understanding the island’s evolution and quantification of sand accumulation will further efforts to model the Grand Strand coastal system.