THREE DIMENSIONAL GEOLOGIC MAPPING WITH GROUND PENETRATING RADAR, TILLMAN SAND RIDGE HERITAGE PRESERVE, JASPER COUNTY, SOUTH CAROLINA

High-resolution LiDAR data and ground-penetrating radar (GPR) have revealed complex geomorphic features on the flood plain of the Savannah River near the Tillman Sand Ridge Heritage Preserve, Jasper County, South Carolina. LiDAR data show that Quaternary eolian sand dunes, as old as 32 ka, overlie Miocene to Pleistocene sediments. High-resolution LiDAR data show dunes and multiple fluvial terraces. These terraces dip slightly to the south coincident with a regional tectonic tilting that induced a southwest migration of the Savannah River. Five ground penetrating radar (GPR) lines were collected for a total of 6.9 line-km on the flood plain south of State Highway 119 and north of the intersection of Forks Lake Road and River Road. Two of the 25 MHz GPR profiles that were collected roughly normal to the Savannah River show that the eolian dunes are thin (< 6 m) and cover Pleistocene marine or marginal-marine sediments. Strong reflectors seen in the GPR data are demonstrated by auger data to be the following features: (1) the contact between Pleistocene marine sediments and the underlying Miocene marine sediments; (2) discontinuous sub-horizontal beds within the Pleistocene marine sediments; (3) channels cut within Pleistocene marine sediments; and (4) a lower thin bed of carbonate mudstone that undulates across much of the Savannah River flood plain. Several explanations for this undulation include normal faulting (down to the south), karst or karst-like processes (dissolution of clam or oyster clasts), or differential compaction of flood plain mud and sand. The GPR receiver/transmitter antennas are coupled in-line and parallel. This antenna configuration does not allow a common midpoint (CMP) experiment to estimate velocity. To allow depth interpretations of the GPR sections, depth to the limestone observed in the auger core was used along with the reflection time to provide a 0.1 m/nS average velocity for the GPR profiles.