QUATERNARY EVOLUTION OF THE INNER CONTINENTAL SHELF OFFSHORE BETHANY BEACH, DELAWARE

Initial stratigraphic analyses of vibracores located three miles offshore Bethany Beach, Delaware indicates the existence of an exposed/nearly exposed coast-perpendicular lagoon depositional system of probable Pleistocene age. The lagoon is found in an area designated as a former early to middle Pleistocene paleovalley proposed by Williams (1999) and follows an eastward projection of Pleistocene age lagoonal sediments of the Omar Formation as presented in Ramsey (1999). Radiocarbon dates of organic material and basal peats extracted from vibracores within the lagoon range from 33K to 46K years before present. Overlying the lagoon are Holocene fine to coarse shelly sands. These sands form a thin veneer (less than 1 foot thick) of modern sand deposits that overlay transgressive sequences of gray colored fine silty sands and organic rich silty clays of fluvial-tidal-lagoon origin. Outcrops of the fluvial/estuarine Tertiary Beaverdam Formation sands are found on the margin of the lagoon. Seismic reflection surveys obtained in 1992 show that the paleovalley proposed by Williams has been reoccupied at least one time since incision and falls within a deeper paleovalley. This study is one of the first to document the presence of late Pleistocene lagoonal deposits offshore Delaware. The lagoonal deposits may be related to a late Stage 3 high stand of sea level.