GROUND PENETRATING RADAR DEFINES THE HOLOCENE AND PLEISTOCENE GEOLOGY OF THE NORTH CAROLINA OUTER BANKS

The Pleistocene and Holocene geologic framework of the North Carolina Outer Banks exerts a fundamental control on modern patterns of shoreline erosion and barrier island dynamics. The shallow subsurface geology of the barrier islands is being mapped through a cooperative investigation involving East Carolina University, the U.S. Geological Survey, and the N.C. Geological Survey. Scientists from the East Carolina University Geology Department recently performed approximately 100 km of ground penetrating radar (GPR) surveys on the Outer Banks from Kitty Hawk to Nags Head. Surveys were performed using a GSSI (Geophysical Survey Systems, Inc.) 100 MHz antenna in monostatic and bistatic mode, and a GSSI 200 MHz antenna in monostatic mode. Ongoing investigations will continue southward and include Cape Hatteras and Cape Lookout National Seashores. The GPR data provide examples of facies that are expected in the National Park Service land. Radar penetration was variable as a result of widely varying geologic and hydrologic properties of the sediments. Maximum subsurface penetration was approximately 20 meters. Numerous facies, bedding planes and stratigraphic relationships of depositional and erosional horizons are clearly delineated in areas with significant penetration. Preliminary interpretations reveal the following specific depositional facies: Beach ridges and beach ridge sets; possible inlet fill or spit progradation facies (characterized by steep, unidirectional prograding clinoforms); channel cut and fill facies (fluvial and inlet); estuarine fill facies; coastal dune facies (complex bed-sets with variable dip directions and multiple reactivation surfaces); beach facies (planar, low-angle, seaward-dipping reflectors); washover facies (planar, low-angle landward-dipping topset reflectors terminating in steeply inclined landward-prograding clinoforms); and marsh peats. It is evident that antecedent Pleistocene topography plays a significant role in defining Holocene depositional patterns on the Outer Banks.