Transect cross section A-E
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Holocene sediment |
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Integrated stratigraphic cross section combining interpretation of seismic data, ground-truthed by coring, with a coastal cross section based on vibracores. Cores in the offshore transect have no cross-shelf correlation potential because they commonly sample different ridge deposits, shown in side-scan sonar imagery and bathymetry data. This transect is just north of the rocky coastal headland in the Venice, FL, area and is similar to the Sand Key transect #3 just north of Indian Rocks Beach. In both areas a narrow barrier island and back-barrier lagoon are positioned against the rising bedrock surface. However, the nearshore settings at 5 km from the beach are quite different. Off Sand Key, sand ridges are present in water depths of 5 to 6 m. In contrast, the cross section here reveals undetectable sediment cover nearshore in twice the water depth, 10-11 m, and a steeper offshore gradient. The volume of sand contained in the barrier-island section is similar to that in a single offshore sand ridge.
In the subsurface, deformed limestone bedrock is attributed to mid-Cenozoic karstic processes. This stratigraphic interval is truncated by a relatively flat erosional surface that regionally forms the base of the Holocene section. Overall, the base of the Holocene is extrapolated from vibracore data that supports the seismic interpretations.