THE DISSOLUTION OF CALCIUM CARBONATE BENEATH THE LOWER COASTAL PLAIN OF MYRTLE BEACH, SOUTH CAROLINA

The lower Coastal Plain of the northeastern South Carolina Coastal Plain is underlain by a series of mixed siliclastic and carbonate sediments. This study provides information related to the dissolution of the carbonate materials during the Quaternary with the implications of surface elevation changes. Over time carbonate-rich shore face sediments have been leached out of the near-surface sediment column. Dissolution occurs from carbonic (from rainwater) and organic acids (from decay and humic substances) mixing with subsurface materials over time. Six sediment samples were obtained from a 3.6-m vibracore from the Murrels Inlet area; three samples from coarse-grained sections of the core were taken above the dissolution front, and three samples from coarse-grained areas were taken below. The samples were sieved, and the samples with carbonate materials were treated with HCl, washed, dried, and sieved again. As expected in this region, coarse sediments were found to have a much higher concentration of calcium carbonate and finer sediments contained less leachable material. The moderate relationship between grainsize and percent calcium carbonate in these shoreface deposits was used to estimate total loss above the dissolution front. Assuming the coarse grained sediments had approximately 55% volume loss, and fine sediment had nearly 2% dissolution, an approximately 9-cm lowering of the ground level could be expected in this area through carbonate dissolution. As the dissolution front migrates through the remaining sediment, it is estimated that an additional 15-cm of surface lowering will be realized.