PALEOENVIRONMENT AND LATERAL EXTENT OF AN EXPOSED CARBONATE BUILD-UP: INTRACOASTAL WATERWAY, HORRY COUNTY, SOUTH CAROLINA

The Intracoastal Waterway is located in Horry County, South Carolina. The research site is an exposed carbonate build-up estimated to be Pleistocene to Pliocene in age. Little research has been performed in the area to document the existence of this build-up. Prominent formations in the area consist of the Waccamaw and the Canepatch Formation. A distinct sand layer is present horizontally between the build-up and the Waccamaw Formation, which consists primarily of fossil mollusks and echinoderms.

The goals of this study are to describe the paleoenvironment and lateral extent of the carbonate build-up. This research will attempt to discover the specifics of this poorly documented carbonate build-up. Field observations show that the carbonate build-up is comprised of shell fragments, predominantly mollusk, in a mud matrix. Thin sections analyzed, using a petrographic microscope, determine the origin of cementation of the build-up in addition to the fossil content. Preliminary thin-section analysis revealed fossils other than mollusk, such as foraminifera and bryozoan. The Mg/Ca ratio, determined using atomic absorption, provides an indication of cement morphology. This ratio is used to infer the temperature and salinity during the time of deposition, providing insight into the depositional environment. Oxygen isotope data is collected to provide confirmation of the depositional environment inferred by the Mg/Ca ratio. The weight percentage of carbonate grains versus clastic grains is used to indicate paleoenvironment. A percentage of approximately 60-70% carbonate grains were determined by dissolving a sample of the build-up in. GIS data is also collected to aid in determining the lateral extent of the exposed build-up. The lateral extent was mapped to be approximately 12 km. Analysis of the carbonate build-up provides a further understanding of sedimentary formations within South Carolina.