Carolina Bays in Horry and Marion Counties, South Carolina

Abstract

Carolina bays are exceptionally well developed in Horry and Marion counties, South Carolina. Depositional surfaces of coastal and fluvial origin have been mapped in this area, and the stratigraphy is reasonably well known above the Pee Dee Formation (Cretaceous). Bays occur on 7 sand-rich surfaces, all pre-Recent in age. Three bay types have been recognized: flat interfluve, dune depression, and terrace contact. The majority of bays in the study area belong to the first type. These bays are underlain by sand cemented with humate which forms an impermeable layer close to the surface. This perches the water table, thereby allowing development of shallow, wet depressions in sandy terrain. The size ot depressions appears to be partly controlled by the width of the interfluve and degree of relief created by dissection of the depositional surface. The two other bay types are located in favorable topographic depressions initiated by dune deflation or damming by fluvial deposition. Drilling in and around bays shows no evidence of solution and subsidence in spite of the presence of carbonate-rich strata in the subsurface and some very localized sinkholes of irregular shape and considerable depth (+20ft). It is postulated that Carolina bays in this area developed from shallow lakes (1 to 6 ft deep) during the mid- to late-Wisconsin in a period when vegetation cover and drainage systems were undergoing considerable change. However, there are many unanswered problems of bay development, including the degree to which they are analogous to contemporary oriented lakes (for example, in Alaska). Stabilized parabolic dunes in river valleys indicate that SW. and WSW. winds blew across bays during their formative period. A similar hydrodynamic system to that recognized in Alaska may have existed in the shallow water bodies of ancestral bays, and led to development of elongated shapes and sand rims.