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Abstract

Outcrop and marine field work on the NW part of the Caicos platform illustrates Pleistocene-Holocene accretion of the Providenciales and West Caicos Islands, the effects of the Holocene transgression on the flooded substrate, and the differentiation of sedimentary provinces in relation to prevailing current direction and inherited topography.

A marine field study of 2D seismic (CHIRP) sub-bottom profile data and surface sediment sampling on the shelf north of Providenciales and North Caicos, and on the platform interior south of Providenciales provide an image of the top-Pleistocene surface, the thickness of Holocene sediments, and the present distribution of facies, biogenic components, and grain sizes. A pronounced difference in the composition and grain sizes of Holocene sediments exists between the open shelf north and the platform interior south of Providenciales, but maximum thicknesses of approximately 2 meters are similar. On the back-reef shelf, peloidal nearshore sands grade seaward to coarse skeletal sands, rocky bottoms and reefs. On the platform interior, the sediments are peloidal and skeletal on or near beaches, coarse skeletal grains and rubble near patch reefs, and peloidal grainstones and mud-lean packstones elsewhere in the subtidal environment.

Outcrop mapping and Uranium-Thorium age dating of carbonate material from Providenciales and West Caicos provide constraints on island growth and sequence development during the Pleistocene and Holocene. Providenciales has two discontinuous core ridges of eolian and subtidal deposits with ages ranging between 160 and 302 Ka. Cutting the island core and prograding away from it are shingles (up to 4 parasequences) of marine and eolian sediments deposited during 140-90 Ka representing the transgression and high stand of isotopic stages 5e and c. Comparison of the elevation of Pleistocene marine deposits (> 12 m) and published sea level curves for the area indicates the need for uplift or higher sea levels for the island. Holocene eolian ridges, beaches, and strandplains form a discontinuous outer shingle on the island. West Caicos is cored by two eolian cores with similar age sediments (219-136 Ka), followed by reef and beach growth (120-130 ka) and younger Holocene eolian ridges making up the east and northeast extension of the island.

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