Integrated stratigraphic cross section combines line-drawing interpretation of seismic data, ground-truthed by coring, with a coastal cross section based on vibracores. Overall, the base of the Holocene is extrapolated from vibracore data that support the seismic interpretations. Additional evidence includes hardbottoms (pre-Holocene bedrock) and probe-rod measurements of sediment thickness. The location of the barrier islands is correlated with a rise in the underlying pre-Quaternary bedrock consisting of Miocene limestone intermittently overlain by Pleistocene facies. Offshore, vibracore USGS-95-48 penetrated a valley structure containing an unusually thick Holocene infill. Such depressions containing Holocene fill are rare and are attributed to both karst processes and erosion of channels. The depressions can also be preferred sites of Pleistocene lime mud accumulation. The shelf farther south from the Indian Rocks Beach headland exhibits an increase in channel and valley-fill structures.
