SEDIMENTOLOGY OF SHORELINE EROSION EXPOSED SOIL HORIZONS ALONG THE ALABAMA GULF COAST

Beach areas on Dauphin Island and Fort Morgan peninsula in Alabama have recently undergone shoreline erosion exposing underlying “paleosoil” horizons. The exposure on Dauphin Island is similar to, and likely a continuation of, a 300 year old soil that was first exhumed in 1995 when extensive shoreline erosion threatened to undercut the island's fishing pier. At that time, the beach was partially closed due to the exposure of numerous in situ tree stumps that were exposed in the surf zone of the public beach. The current exposure is less obvious because of fewer tree stumps and less extensive sand loss. The uppermost layer of the new soil exposure is 20 cm thick, gray-black in color and consists of carbonaceous, well sorted, medium sand. The lower layer consists of yellow-brown, moderately sorted, medium sand that is partially lithified by secondary limonite precipitation. Some kaolinite is also contained within layer two. We believe that the soil exhumed at Dauphin Island corresponds to the ‘A' and ‘B' horizons of a typical quartz sand-derived pedalfer soil. The soil exhumed on Fort Morgan Peninsular is currently being examined but is more organic than the Dauphin Island exposure. The Fort Morgan exposure also has numerous tree stumps visible in the surf zone. Pollen analysis on the peat and radiocarbon dating of the uncovered stumps will indicate the vegetation assemblage and approximate date associated with this paleoenvironment.