Elevation of the regional transgressive unconformity underlying the inner shelf of Long Bay (Grid; transgr_grd)

In 1999, the U.S. Geological Survey (USGS), in partnership with the South Carolina Sea Grant Consortium, began a study to investigate processes affecting shoreline change along the northern coast of South Carolina, focusing on the Grand Strand region. Previous work along the U.S. Atlantic coast shows that the structure and composition of older geologic strata located seaward of the coast heavily influences the coastal behavior of areas with limited sediment supply, such as the Grand Strand. By defining this geologic framework and identifying the transport pathways and sinks of sediment, geoscientists are developing conceptual models of the present-day physical processes shaping the South Carolina coast. The primary objectives of this research effort are: 1) to provide a regional synthesis of the shallow geologic framework underlying the coastal upland, shoreface and inner continental shelf, and define its role in coastal evolution and modern beach behavior; 2) to identify and model the physical processes affecting coastal ocean circulation and sediment transport, and to define their role in shaping the modern shoreline; and 3) to identify sediment sources and transport pathways; leading to construction of a regional sediment budget. This data set contains a surface depicting the elevation of the regional transgressive unconformity underlying the inner shelf of Long Bay, offshore of the South Carolina Grand Strand. Chirp seismic data collected with Benthos SIS-1000 and Edgetech SB-512 acquisition systems were processed using SIOSEIS (Scripps Institute of Oceanography) and Seismic Unix (Colorado School of Mines) to produce segy files and jpg images of the profiles. Data were then imported into Landmark SeisWorks, a digital seismic interpretation package, where the sea floor and underlying transgressive surface were interpreted and digitized. The isopach between these horizons was exported at every 50th shot as xyz points, and imported to ArcGIS for interpolation into a 10-m raster grid. The isopach grid was then subtracted from a seafloor bathymetry grid (bathy_grd) to approximate the proper elevation of the transgressive unconformity beneath the sea floor.