FRAMEWORK GEOLOGY OF THE NORTH ISLAND SPIT OF NORTHEASTERN SOUTH CAROLINA

As part of the USGS-South Carolina Sea Grant Consortium Coastal Erosion Program, this study examines the geologic development of the North Island spit, located seaward of Winyah Bay in northeastern South Carolina. This prominent spit, which is over 5 km in length and 1 km in width, has developed as a series of southward prograding, recurved shorelines located at the southern terminus of the 75 km long Grand Strand coastline. Measurements of sediment thickness and rate of shoreline progradation of this feature will not only allow for a better understanding of regional sediment transport along the Grand Strand system but also sedimentary processes active in the formation of a spit.

To determine sediment thickness and framework geology of the spit, ground-penetrating radar was collected along the length of the spit and along three shore-normal transects and vibracores were collected at 15 locations. Cores were split, photographed, and visually described for color, texture, grain size, organic components, and bedding. To determine the age of paleoshorelines, basal dune sands were analyzed for luminescence age estimates and shells were sent for radiocarbon analysis.

GPR data reveal that the spit is composed of 2-8 m of uneven reflectors that were determined from cores to be composed of fine sand. These reflections overlay steeply southward dipping reflectors, which extend beyond 10 m depth and are composed of bedded shelly sand. The upper unit is interpreted as representing the upper spit platform and subaerial dunes, while the lower section is channel infill. Except for a small channel at the northern end of the spit, spit progradation appears to be continuous to the south. When combined with age estimates, this project will allow for a better understanding of regional sedimentary transport and processes affecting the Grand Strand and as well as other coastal systems.