PRELIMINARY CHARACTERIZATION AND MAPPING OF LATE CENEZOIC MARINE-ESTUARINE SEDIMENTS IN THE UPPER TAR RIVER WATERSHED IN THE FALL ZONE OF NORTH CAROLINA

Investigation of a 3000-acre study area revealed clay-rich sediments up to 5 meters in thickness in the upper Tar River watershed in the fall zone of North Carolina. Extensive drilling and Geoprobe_TM coring identified two distinctive sedimentary units across the study area. The lower unit consists of dense, kaolinitic, clay beds with symmetrical wave formed structures and mud cracks and a thin basal sand bed overlying gneissic and granitic bedrock-saprolite. Angular and well-rounded quartz gravels are typically found at the contact between the basal sand and bedrock-saprolite. The lower unit is overlain by a massive clayey upper unit containing abundant quartz and feldspar sand grains. Near streams the upper unit is absent and the lower unit is truncated with common buried organic soils at the upper boundary and covered by 1-2 meters of historical, agricultural legacy sediment. Stream-to-ridge transects found the truncated lower unit in stream floodplains, upper and lower units in mid-slope terraces to 5 meters in thickness, and thin (<1m) caps of the lower unit on ridge tops. Exploration of 30 miles of the upper Tar River identified several additional locations of similar clay-gravels-bedrock/saprolite sequences. A preliminary GIS map of the two sediment units was developed for the study area. Using existing geologic and soil maps, the sedimentary units are tentatively associated with known Late Cenozoic marine-estuarine sediments east of the study area. Using GIS modeling, the western-most extent of the sedimentary units was estimated for the upper Tar River watershed.