Abstract

This Florida Geological Survey (FGS) study was funded by the National Oceanic and Atmospheric Administration (NOAA). This study characterizes recently sampled sediments from the beaches of Pinellas, Hillsborough, Manatee, Sarasota, Charlotte, Lee, Collier and Monroe counties. A total of 390 samples from 214 sites along the southwest coast of Florida and 33 samples from 28 sites in the Florida Keys archipelago were collected and described. Of those samples, 214 from the southwest coast and 28 from the Keys were also granulometrically analyzed. Photographs, descriptions and the results of granulometric analyses are provided.

The study areas on the southwest coast of Florida and Florida Keys archipelago were broken down into 22 and two reaches respectively. These reaches are defined by geographic boundaries, such as inlets and passes as well as the mouths of rivers, harbors, and bays. The study showed a frequent correlation between these boundaries and significant changes in grain size. Additionally, frequent correlation between these boundaries and significant changes in carbonate percentages were also found on the southwest coast of Florida.

Changes in grain size, both before and after digestion of carbonate material, as well as the percentage of carbonate material in the samples define four regions in the southwest coast of Florida. A direct correlation between the grain size and carbonate percentage curves was seen; in that where carbonate percentages increase so does grain size. A significant separation between the pre and post-carbonate digestion curves was noted where the carbonate percentage curve rises above 25 percent. The carbonate sediment fraction present in the samples are generally coarser than the non-carbonate fraction. While the ratio of carbonate material to non-carbonate material varies substantially, the general trend from north to south along the southwest coast of Florida shows an increase in the percentage of carbonate material within the samples, which broadly peaks in central Sarasota County, central Lee County and at the Lee County/Collier County line and then slightly declines southward to Cape Romano.

The two regions in the Florida Keys archipelago identified within the study area were defined both by the geographic boundary separating the middle and lower Keys and a nearly coinciding distinct change in sediment grain size, with the sediments of the beaches of the lower Keys being the coarser of the two. Sediments collected from the Florida Keys archipelago were almost exclusively carbonate. The only exceptions to this, on Little Crawl Key, Munson Island and Key West, are probably the result of beach replenishment activities. The grain size curve peaks broadly from the Spanish Harbor Keys sample to the east end of Long Beach on Big Pine Key and then, when the effects of beach replenishment are considered and discounted, declines westward.