THE MIXED SILICICLASTIC/CARBONATE INNER SHELF OFF WEST-CENTRAL FLORIDA

Over the past decade, there has been a tremendous amount of research effort directed toward better understanding the geologic framework of the west-central Florida inner continental shelf and barrier island chain. Primary interests driving research in this coastal sector include resource assessment for future planning, and understanding coastal evolution during the late Holocene sea-level rise as it relates to stability of the modern barrier island chain and the origin of offshore depositional patterns. The inner continental shelf seaward of the west-central Florida barrier island chain is unusual in that it is composed of a complex array of linear siliciclastic sand ridges situated upon an ancient carbonate platform.

In the subsurface, deformed limestone bedrock is attributed to mid-Cenozoic karstic processes. This stratigraphic interval is truncated by an erosional surface, often exposed, that regionally forms the base of the Holocene section. The Holocene section is thin and discontinuous, dominated by low-relief sand-ridge morphologies (0.5 to 4 m’s of relief) with ridge widths on the order of 1 km and ridge spacing of a few kilometers. The sedimentary facies in this system consist mostly of redistributed relic siliciclastics, local carbonate production, and residual sediments derived from erosion of older strata. Inter-ridge areas display a variety of hardbottom types important to marine ecosystems. The variability and dynamic character of bottom environments along this inner shelf are just beginning to be understood. Although considered a low-energy environment, both the long-term response and short-term behavior of sand-ridges reflect a response to high-energy seasonal events (winter frontal passages).

There are distinct segments of this inner shelf depending upon shelf depth and landward coastal type. These coastal sectors exhibit varied styles of coastal evolution during the Holocene transgression suggesting a spatial and temporal combination of back-stepping barrier-island systems combined with open-marine low-energy coastal environments. Antecedent topography of the ancient carbonate platform exerts a fundamental control over the distribution of shelf depositional products.