PLEISTOCENE BRAIDED-RIVER DEPOSITS FROM THE INNER PIEDMONT OF SOUTH CAROLINA

Deposits of fluvial sands and gravels were studied along the shoreline of Lake Hartwell and at a construction site for a new building in Clemson, South Carolina. The sands and gravels are located 15-20 m above the most recent course of the Seneca River, which is now flooded by Lake Hartwell. The deposits range from 1-2 m in thickness above saprolitic biotite gneiss. Based on detailed sedimentological logging of these deposits, three distinct units, each containing specific facies, are present: a massive gravel unit above the basal unconformity; a middle sand unit containing abundant cross bedding; and an upper unit of clay-rich sand with few internal structures. Origin of the deposits is interpreted as braided river based on the vertical succession and facies analysis. This river system is interpreted as having formed in response to high sediment load derived from Pleistocene drainage, probably associated with snowmelt from nearby mountains. Analysis of topography surrounding the Seneca River valley prior to creation of Lake Hartwell has revealed several alluvial terraces that are now partially obscured by the lake. Results of this investigation suggest that the river evolved from depositional to erosional as sediment load decreased with climatic warming.