Uninterpreted seismic profile illustrates the poor acoustic contrast between the
Holocene sediment cover and the Pleistocene exposure surface. The poor contrast is
typical throughout the region and is attributed to the karst and weathered nature of
the underlying pre-Quaternary bedrock. Overall, the base of the Holocene is extrapolated
from vibracore data that supports the seismic interpretations. Additional evidence
includes hardbottoms (pre-Holocene bedrock) and probe-rod measurements of sediment
thickness. The modern sediment cover is usually less than 2 to 3 m thick, corresponding
with the higher-relief portions of the sand waves or ridges seen here. In this area,
the thickest sand deposits were found at the offshore end of the survey in greater
than 15 m water depth.