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The Coastal/Inner Shelf System—General FeaturesThe west-central barrier-island coast includes two large estuarine systems (Tampa Bay and Charlotte Harbor) and two headlands (Indian Rocks and Venice; Figure 1). The Venice headland is a mainland beach with dark, phosphate-rich sediments of Neogene age directly cropping out along the inner shoreface. Additionally, Miocene limestone is exposed along the mainland shore at Indian Rocks. North of the barrier-island system is the Big Bend marsh-dominated coastline—a coastal system with such a low gradient (1:5,000) that it has been referred to as an incipient epicontinental sea (Hine et al., 1988). The inherited gradient from the underlying ramp off the west-central barrier-island system is slightly steeper having gradients of ~1:2,000. With the deeper water closer to the beach, the sandy coast has higher wave energy than the marsh-dominated coast that rests on the flatter gradient. Both coastal types are low-wave energy coastlines when compared to most parts of the US Gulf and east coasts. In addition, the relatively small fetch of the Gulf of Mexico and the prevailing easterly winds contribute to the overall low wave-energy character of the coastline. However, occasionally potent extratropical and tropical storms have made significant impact (Davis and Andronaco, 1987; Davis, 1994; Goodbred and Hine, 1995; Davis, 1994). The coast is also microtidal as defined by Davies (1964) and Hayes (1979), although as pointed out by Davis and Hayes (1984), it has many prominent mixed-energy features such as "drumstick" shaped barrier islands and two very large ebb-tidal deltas associated with the mouths of the two estuaries. Indeed, it is the great range in size of the back-barrier estuaries and lagoons that dictates the wide range of inlet types along this coast. Topographic variations of the pre-Holocene surface have played a strong role in the distribution of the estuaries, headlands, and controlling the size of back-barrier bodies of water (Evans et al., 1985). Very little was known about the inner shelf prior to this study other than the fact that the sediment cover was spotty and that there were large expanses of limestone, which supported benthic communities (Riggs and O'Connor, 1974; Doyle and Sparks, 1980). Rock ledges and sinkholes were also known to exist, yet their control by the underlying stratigraphy was unknown. Additionally, sediment distribution on the inner shelf in any predictable pattern, the existence and nature of sand bodies, sediment types in these sand bodies, the degree, if any, of antecedent topographic control on sediment distribution, and the frequency of sediment transport activity all were essentially unknown. |
