INTEGRATED LIDAR AND GEOELECTRICAL MAPPING OF RELICT BRAIDPLAIN AND DUNE DEPOSITS ALONG THE TAR RIVER, NORTH CAROLINA

The surficial sediments of the Northern Province of the Inner Coastal Plain of North Carolina are extensive yet their spatial distribution and stratigraphy are poorly understood. This has been attributed to poor preservation, lack of outcrops, dense vegetative cover, land alterations, the lack of dateable material, dissection by streams, and burial by wind-blown deposits. These sediments are typically Pliocene and younger and can provide evidence of past climate and sea level changes. Common deposits include braided and meandering river sediments, floodplain sediments, dune sands, and marine and estuarine sediments. Recently, Light Detection and Ranging (LiDAR) data have become available for the Coastal Plain through the NC Floodplain Mapping Program. These data provide elevation maps at a vertical resolution of 0.25m. A GIS analysis was performed using LiDAR data paired with county soil survey data to map surficial deposits in the Tar River Basin, NC. The combination of soil and elevation coverages were used to locate sedimentary deposits within the basin and helped differentiate terraces from the active floodplain. Braided river deposits, paleomeanders, dune deposits, Carolina Bays, and paleoshorelines were apparent. The asymmetry of the Tar River valley was also evident. Typically, steep bluffs and very narrow floodplains were located to the south of the river, and extensive floodplains and gentle slopes on the north side. Broad regions of braided river deposits, several kilometers wide, were common on the north side of the river. These deposits were often bounded by dune sands. A group of five sites were selected for field verification. Sediment cores collected at the sites verified that LiDAR data reliably located braided river and dune deposits. Electrical resistivity mapping (capacitively coupled) indicated the thickness and extent of braided river and sand dune deposits, typically these deposits were less than 8m thick and were underlain by the Yorktown Formation (Pliocene). Based on the location, thickness, extent, and permeability of these sediments, it is likely that they are an important location for groundwater recharge to the Tar River.