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Framework
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Researchers take vibracore samples to examine sediments lying below the sea-floor.
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The west-central Florida coast barrier-island chain sits near the center of a broad, gently sloping
carbonate platform. The continental shelf is underlain by limestone bedrock with a thin, discontinuous
cover of sand deposits of both siliciclastic (predominantly quartz sand) and carbonate origin. Prior to
the initiation of this project, it was generally believed that sand resources were evenly distributed on
the continental shelf. Early results, however, have demonstrated that sand is concentrated in specific,
near-shore areas and is of limited thickness.
USGS scientists and collaborators have systematically mapped the thickness of sand deposits
near the coast through seismic surveys and jet-probing. The first phase was a regional mapping with
widely spaced geophysical and framework sample data which found that most beach quality sand is
concentrated in active ebb-tidal deltas located just off tidal inlets and in long, linear ridges found on
the inner shelf. Across the entire study area, bottom samples and core samples have been collected,
and are being analyzed to develop a map of sea-floor sediment types. This research indicates that
although there is coarse biogenic carbonate sand being produced in the modern environment, there
is no modern source of siliciclastic sediment in this region.
In addition to the reconnaissance mapping, USGS scientists and collaborators have completed
detailed mapping studies in two localities, one north and one south of the entrance to Tampa Bay.
Detailed side-scan sonar maps were made of localized areas which are being used to understand the
variability in sediment distribution of beach quality sand, carbonate shell material, and hardgrounds
and shed new light on the processes that shape the inner shelf.
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