A reassessment of the late Quaternary surficial geology of the lower Delmarva Peninsula, Virginia

Abstract

This study provides insights into the age, extent, and depositional history of a 23 kilometer-long sequence of eolian sands that overlies a paleosol of previously undetermined age along the southwestern margin of the Delmarva Peninsula, VA. References in past literature and maps suggest that these sands were deposited during the rapidly changing deglacial period of the late Pleistocene. However, recent discovery of organic materials within the paleosol and in-situ cultural artifacts within overlying sediments challenge the past interpretations of this landscape. Using a combination of stratigraphic, sedimentologic, airborne LIDAR, ground-penetrating radar, and radiocarbon data, the age and extent of this surficial sequence were investigated at 5 locales within the study area. The results suggest the following: 1. Grain-size, color, texture, and sedimentary structures indicate that there are two unique dune sequences within the study area and are laterally continuous from Savage Neck to Latimer’s Bluff, VA. 2. The most recent airborne LIDAR data depict these dunes as a topographically high, narrow, discontinuous, parabolic field that extends several hundred meters inland, easily delineated from the surrounding landscape based on the abrupt change in slope (i.e., 54 degrees to 5 degrees). 3. A ground-penetrating radar profile beginning at the Chesapeake Bay shoreline and terminating 140 meters inland at the Savage Neck study locale shows a buried surface consistent with the expectations of the lateral extent and depth of the paleosol beneath the overlying sands. 4. Cultural artifacts found within the paleosol and 3 organic samples selected for radiocarbon dating provide a time constraint for the sequence that suggests the dune transgression over the paleosol began 1100 years ago and continued to actively migrate within the last few hundred years. The sum of our data suggests that the eolian sands in the study area do not belong to the late Pleistocene, but instead were deposited during a period when this landscape was assumed to have been relatively stable. The unexpected age of the paleosol raises questions about the processes that would have led to increased eolian transport over such a broad area. Natural and/or anthropogenic burning, protracted drought, and tidal amplification within the Chesapeake Bay are discussed as possible mechanisms that may have contributed to this expansive deposit while operating in an otherwise relatively stable environment.