THE USE OF GROUND PENETRATING RADAR IN QUATERNARY SEA LEVEL STUDIES: AN OVERVIEW FROM THREE INVESTIGATIONS IN THE DELAWARE AND CHESAPEAKE BAYS, USA

Ground penetrating radar (GPR) has proved to be an invaluable tool in investigations of Quaternary coastal stratigraphy in the siliciclastic sediments of the mid-Atlantic coastal plain of North America. In this region, the identification of highstand deposits of individual Pleistocene sea-level events is often difficult. Numerous highstand sequences are superposed, both vertically and laterally, in the subsurface of the modern coastal environment. Natural and artificial subsurface exposures are rare, and the geomorphic expression of these ancient deposits is often subtle. Identification of distinct highstand deposits from cores and boreholes is also difficult due to lithologic similarities between deposits, and the scarcity of suitable dating materials.

GPR has been successfully used in thin successions of exposed estuary-margin sediments in the region, to delineate unconformity-bound, climate-induced highstand deposits from distinct sea-level events in the mid to late Pleistocene. Radar records revealing the internal structure of these deposits have allowed for sequence-stratigraphic interpretations, with the identification of transgressive, highstand and regressive systems tracts. The separation of multiple minor sea-level fluctuations, within an overall sea-level event (oxygen isotope stage), has also been possible.

The lithology and sedimentary structures recognized in these high-resolution records have been used to interpret varied coastal depositional environments and geomorphic structures. Bay bottom, nearshore, foreshore, shoreface, dune and backbarrier lagoon/marsh environments have been imaged, as well as nearshore bar, foreshore bar, barrier-island beach and shoreline escarpment structures. Buried paleovalleys of rivers and tidal creeks imaged with GPR establish cross-cutting relationships with adjacent highstand deposits, and provide a contrasting lowstand record in Quaternary sea level studies.

Examples of published and new data from three investigations on the exposed margins of the Delaware and Chesapeake Bay estuaries in New Jersey and Maryland are presented.