COARSE FRAGMENT RE-DISTRIBUTION IN THE GENESIS OF SOME FALL ZONE CAROLINA BAYS

Detailed investigations were conducted of Carolina Bay features, which are formed over Coastal Plain Sediments and Saprolites in the Middle Coastal Plains of Johnston County, North Carolina. In this soil system the Coastal Plain sediments and saprolites occur in complex patterns. Gravels, cobbles and small stones occur at the Coastal Plain-Saprolite contact as well as in isolated lenses in the sediment units. These bay features contained characteristic coarse textured secondary rims and as well as fine textured sediments within bay depressions. The bays originated as shallow depressions at the head of drainage ways. The original depressions were defined in part by buried A horizons. Water levels in these features were sustained by the blocking of drainage outlets by secondary rim formation. Water depths ranged from about 30 cm to slightly less than 1 meter in two of these features. These bays differ from most other bays as reported in that they secondary rims contain coarse fragments or in one case consist mainly of coarse fragments. These fragments are predominantly sub-rounded quartz fragments with lesser amounts of well-rounded fragments. Overall fragment size ranged from 2 cm to more than 35 cm (long axis). The source for these coarse fragments was the adjacent saprolite highs and Coastal Plain sediments that were truncated during expansion and formation of the bays. Some of these fragments appear to have been transported a distance of more than 100 meters. Processes associated with ice push are considered to be a likely mechanism for the transport and deposition of these coarse fragments as was proposed by Bliley and Burney (1988). Other evidences suggest that ice push may be a critical factor in the formation of Carolina Bays. This study confirms that the processes for coarse fragment re-distribution are more wide spread than previously reported. LIDAR imagery was particularly useful for the identification of subtle topographic features in this study.