STRATIGRAPHIC, HYDROLOGIC, AND CLIMATIC INFLUENCES ON THE FORMATION AND SPATIAL DISTRIBUTION OF CAROLINA BAYS IN CENTRAL DELAWARE

The occurrence of thousands of circular features, herein referred to as Carolina Bays, at the land surface in northern Delaware presents an interesting mapping challenge. There are many theories concerning the origin of Carolina Bays, from meteorite impacts to buffalo wallows. The general consensus is that they are the result of interaction between periglacial winds, groundwater levels, and exposed water table, but the exact mechanism remains unknown. Limited evidence in Delaware indicates that these features are late Pleistocene in age. Radiocarbon dates from three Carolina Bays in northern Delaware indicate deposition prior to 11,000 yrs B.P., followed by a break in deposition.

In northern Delaware, Carolina Bays are difficult to recognize in the field and on topographic maps due to their low relief. On average, from base to rim top is less than 1.5 m. Carolina Bays are characteristically a very thin (< 1 m thick) overprint on the older, thicker deposits; they are typically less than 500 m in diameter. The recent availability of high-resolution LiDAR (Light Detection And Ranging) reveals these features in greater detail than ever before. LiDAR images show that in northern Delaware, Carolina Bays occur in a belt roughly parallel to the strike of the subsurface Neogene and Paleogene deposits. These findings have raised questions about the possibility of a larger regional geologic control over Carolina Bay density and for perpetuation of these features as wetlands. Given that the surficial deposits are of similar lithology (predominantly sand), we hypothesize that the control is related to the thickness of the surficial deposits and/or their location over a particular lithologic configuration (the updip limit of the lower clays of the Calvert Formation).