Abstract

This is a Florida Geological Survey (FGS) study funded by the National Oceanographic and Atmospheric Administration (NOAA). This study characterizes recently sampled sediments from the beaches of Brevard, Indian River, St. Lucie, Martin, Palm Beach, Broward and Miami-Dade counties as well as those sampled previously. The prior sampling effort was part of a multi-year study titled “A Geological Investigation of the Offshore Area Along Florida’s Northeast Coast, under MMS/FGS Cooperative Agreement No. 1435-0001-30757.” That study included the characterization of sites in Nassau, Duval, St. Johns, Flagler and Volusia counties. In both sampling efforts, a total of 842 samples from 400 sites were collected and described. Of those samples, 609 were also granulometrically analyzed. Photographs, descriptions and the results of granulometric analyses are provided.

The study area was broken down into 18 reaches defined by geographic boundaries, such as inlets and the mouths of rivers. The study showed a frequent correlation between inlets and significant changes in mean grain size and carbonate percentage. Changes in mean grain size, both before and after removal of carbonate material, as well as the percentage of carbonate material in the samples define five regions in the study area. A moderate positive correlation between mean grain size and carbonate percentage curves was observed. The carbonate sediments present in the samples was observed to be coarser than the non-carbonate fraction. This difference in mean grain size appears to be most significant where the carbonate percentage rises above 50 percent. While the ratio of carbonate material to non- carbonate material varies substantially north of False Cape in Brevard County, the general trend from north to south shows a steady increase in the percentage of carbonate material within the samples until Government Cut in Miami-Dade County is reached. After Government Cut, there is a substantial and abrupt decline in carbonate material.