The Holocene carbonate sediments of Cape Sable, Florida, form a facies mosaic in which facies are controlled by frequency and duration of flooding. The 4 following zones occur:

  1. Flooding 0–5% of the time (supratidal)—massive to crudely bedded sandstone or siltstone, abundant birdseye, low species diversity, high abundance of single species with uniform-sized individuals.

  2. Flooding 5–25% of the time (high intertidal)—low domal and flat laminated algal stromatolites, desiccation cracks and flat laminated pebbles, low species diversity, low abundance of individuals, microscopic invertebrates only.

  3. Flooding 25–90% of the time (low intertidal)—massive burrow-mottled silts, moderate species diversity, moderate abundance of individuals, mainly microscopic, with a wide size range among individuals.

  4. Flooding > 90% of the time (subtidal)—massive pelletal silts and clays, highly burrow-mottled, high species diversity, high abundance and wide size range of individuals within species, many macroscopic invertebrates. Areas of high intertidal and supratidal sediments where ponding of waters occurs for extended periods are characterized by single or multiple algal and sediment laminae much thicker than in areas where waters drain rapidly.

Sedimentation in zone 1 forms thin beds, derived from sediment-laden waters driven over the area during storms. In Zone 2, sediments are deposited in thin laminae; sedimentation is controlled by the trapping of particles carried by tidal currents and binding them onto mats of blue-green algae. Sedimentation in zone 3 occurs mainly in the form of thin beds deposited during storms and subsequently reworked by organisms. In zone 4, deposition occurs by settling of (1) in situ sediments; (2) particles carried into the area by tidal currents; and (3) particles from sediment-laden storm waters.

Measurement of production of calcareous sediment within the Cape Sable area, measurements of the net transport of sediment into the area by tidal currents, and measurement of the volume of sediment deposited in the area since its opening to the sea in the 1920s allow the following calculations to be made. Since 1920, 4% (0.01 cm/yr) of the total deposit has been derived from in situ production, 34% (0.28 cm/yr) by net transport into the area on tides, and 62% (0.50 cm/yr) by storms.

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