CAROLINA BAYS IN JORDAN QUADRANGLE, CLARENDON COUNTY, CENTRAL SOUTH CAROLINA ARE RELICT SURVIVORS FROM DEVELOPMENT OF SINKHOLES DUE TO KARSTIC SOLUTION

Dominant features of the surface in Jordan 7.5-minute quadrangle in south Clarendon County, South Carolina are: a terrace underlain by the informal, marine, upper Pliocene Marietta unit; a part of the Wicomico terrace underlain by marine or fluvial, early Pleistocene sediments; a terrace underlain by late Pleistocene fluvial sediments of Santee River valley; incised valleys of tributaries to Santee River (in the south) and Pocataligo River (in the north); alluvium in Santee River valley; and Lake Marion (flooded Santee River valley). Smaller, irregularly shaped to rounded, shallow depressions abound on the older two terraces but appear to be absent on younger terraces. Some irregular to round depressions merge with irregular to rounded valley walls of the tributaries. Carolina bays have the typical ovoid shape, NW-SE orientation, and sand rims. Well-defined Carolina bays are scattered in northern Jordan quadrangle and are fewer in more deeply incised, central and southern Jordan quadrangle.

Three calcareous formations occur at shallow depth in parts of Jordan quadrangle. The middle Eocene Warley Hill Formation is partly calcareous, glauconitic, quartzose sand. The middle Eocene Santee Limestone is almost entirely calcareous. The lower part of the Pliocene Duplin Formation is locally calcareous. From zero to three calcareous formations occur at shallow depth (less than 80 ft) in Jordan quadrangle. Abundant irregular to round depressions, irregular and rounded courses of tributaries, and the near-surface local occurrence of three calcareous formations are evidence for development of sinkholes by karstic solution (after Davies and others, 1986, USGS, karst map; after Willoughby, 2003, SCGS, geologic map).

The small number and lower density of Carolina bays and comcommitant large number and high density of sinkholes in Jordan quadrangle contrast with neighboring quadrangles, in which calcareous sediments occupy less subsurface area or are absent in the shallow subsurface (less than 80 ft). Karstic solution has been suggested as one possible mechanism for initiation of Carolina bays. In Jordan quadrangle, karstic solution has reduced the number of Carolina bays and is presumed to remain active.