GEOLOGIC MAPPING USING LIDAR, TILLMAN SAND RIDGE HERITAGE PRESERVE, JASPER COUNTY, SOUTH CAROLINA

Surficial geologic mapping in the Savannah River valley, in the vicinity of Tillman Sand Ridge Heritage Preserve, Jasper County, South Carolina, has been greatly facilitated using LiDAR imagery. The LiDAR images reveal numerous geomorphic features not easily recognized in the field, on existing 5-foot contour interval 7.5-min. topographic maps, or on 30-m DEMs. The study area is located within the 6-km-wide flood plain of the southeastward-flowing Savannah River about 50 km from the Atlantic coast. Here, the river is located on the western edge of the flood plain, at the base of a 20-m high escarpment cut into Miocene-to-Pleistocene marine and estuarine strata. East of the modern river, LiDAR data show at least four NW-trending, terrace escarpments, as well as the surface details of vegetated eolian dunes, and numerous abandoned fluvial channels. The oldest and eastern-most escarpment is incised by abandoned meandering fluvial channels that were not recognized on initial field traverses. To the west a series of NW-trending terraces bounded by subtle escarpments can be traced using LiDAR images for upwards of 15 km along strike. These terraces have been incised by evenly spaced southwest-trending fluvial channels presumably formed when the paleo-Savannah River migrated westward in response to falling sea level and/or gentle regional-scale neo-tectonic tilting. Vegetated, non-active, fluvially truncated eolian dunes overlie three of the four terraces. Optically stimulated luminescence age dates range from 40 to 17 ka. The western edge of the dune field is cut by numerous recently abandoned and currently active meanders of the present Savannah River. Ground penetrating radar and auger data indicate that Quaternary fluvial deposits of the Savannah River accumulated on an irregular surface of presumed Miocene age marine strata.