Abstract

A major portion of Florida's Gulf of Mexico coastline is a siliciclastic, sand-starved, low-wave-energy system dominated by marshes that face the open sea. Because of its location at the center of an enormous (350,000 km 2 ), flooded, broad, flat, ancient carbonate platform, this coastline can be viewed as the margin of an incipient epicontinental sea. Within a 65-km sector along this 300-km-long, open-marine marsh coast, four distinctly different morphological sectors have been identified: 1) berm-ridge marsh shoreline, 2) marsh peninsula shoreline, 3) marsh archipelago shoreline, and 4) shelf embayment shoreline. The underlying Paleogene limestone bedrock topography results from karstification and dissolution processes. This antecedent topography and the distribution of actively discharging freshwater springs affect sedimentary processes, facies, and stratigraphic units. The morphology and processes within the four coastal sectors vary as a function of a northerly decrease in the thickness of relict Pleistocene quartz-sand cover and an increase in the complexity and relief of the underlying bedrock topography. Each of the four coastal sectors has a unique distribution of sedimentary products. In addition, each has responded differently to rising sea level--a process that continues to control the spatial distribution of organisms and sediments. However, the sedimentary lithosomes in all four coastal sectors share a similar fate during landward shoreline translation. Within the inner continental shelf, very little of the marsh stratigraphy or large oyster bioherms is preserved. Only those sediments that have accumulated within bedrock depressions or sinkholes have the best chance for long-term retention. Thus, a condensed stratigraphic section is produced. Since only thin and discontinuous sediment accumulations are preserved, the relief and texture of the bedrock surface due to chemical etching and bioerosion must also be used as clues to the recognition of similar coastal systems in ancient settings.

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