GEOPHYSICAL SURVEYS OF A ROBESON COUNTY, NC CAROLINA BAY

A ground penetrating radar (GPR) survey was conducted in Juniper Bay, a 296 ha Carolina Bay located south of Lumberton, NC, in December 2000. Its purpose was to detect the lateral extent of subsurface limiting horizons important to our intentions of restoring this bay to a wetland. We collected continuous data along 57 transects; ground truthing of GPR results was completed with nineteen cores and additional shallower borings. The central and southeastern portions of the bay showed relatively flat-lying clay and organic layers at depths of up to 1.5 m. A buried surface could be recognized in the GPR results. GPR revealed complex subsurface topography in the northwestern third of the bay, including steeply dipping reflectors (A) along the southwest side of the bay and irregular subsurface topography (B) away from the rim. An initial interpretation of our findings suggests an erosional episode caused by stream channelization that cut down into Pliocene and Cretaceous marine units, in the area where the bay later formed. The bay depression formed in sands that buried this erosion surface. Horizontal layers covered the dipping beds, perhaps before bay formation. Irregular topography in the bay could be the result of sediment build-up around vegetation during low water levels, or may be erosional remnants of sediments accumulated during high water levels and eroded during low water levels. Horizons above this irregular topography are horizontally deposited, indicating the recent history of the bay is a period of gradual infilling under wetter conditions that was likely interrupted by drier episodes.