ALLUVIAL FAN EVOLUTION IN THE SANTEE RIVER BASIN (SC) SINCE THE LAST GLACIAL MAXIMUM

The surface of the Coastal Plain of the Eastern US retains a natural record of sea-levels over the last several million years identified by ancient barrier islands, estuaries, and river systems. Overprinted on this original surface, climatic changes through the glacial (cold, dry, low sea level) and interglacial periods (warm, moist, high sea levels), have had lasting impacts by modifying the landscape. When northern North America was under massive ice sheets, the cold and dry savannahs of South Carolina were occasionally barren, allowing for eolian-related systems to develop. This movement of sediment provided the landscape with material to build dunes and other features.

The purpose of this study has been to identify fan-like geomorphic features extending downslope from the mouths of stream systems onto a floodplain surface formed approximately 13,000 years ago. These presumed climate-related features on a section of the Santee floodplain, determined to be alluvial fans in this and other studies, are described and placed into the geological and climatological context of the last ~10,000 years. By investigating the geological construction of the alluvial fans through the use of high-resolution mapping, subsurface analysis with ground penetrating radar and sediment coring, and in the near-future, using radiocarbon dating techniques, a clear understanding of their distribution and geology have be made. The research has identified 28 fan-shaped wedges of sediment extending from the mouth of 32 streams on the north side of the Santee River valley. GPR data combined with LiDAR datasets indicate thicknesses ranging from approximately 5m at the stream discharge area to a feather edge out on the modern floodplain. Lithology of the fans range from coarse to fine sands including finer deposits, sharply transitioning into buried flood plain deposits. Flood plain organics are being dated. Future work will include OSL and additional radiocarbon dates.