Expanded Model for Ooid Form and Genesis: Caicos Platform, British West Indies
Caicos platform is a moderate-sized carbonate platform (100 × 70 km) in the southeastern Bahamian Archipelago, situated in a subarid climate and subjected to brisk prevailing easterly trade winds. Oolitic grainstones of a variety of types dominate Holocene and Pleistocene sediments on this platform. Variations in ooid grain form reflect variations in the type, frequency, and intensity of agitation and the type and intensity of degradational grain processes (boring or micritization).
Typical Bahamian concentrically laminated ooids dominate cross-platform banks swept by daily tidal currents and windward coastlines of the platform interior receiving persistent wave agitation. Fine-grained oolitic grainstones also form the nearshore sands on the beaches on exposed north- and east-facing platform margins that are not overwhelmed by skeletal sands, and the protected beaches on interior south-facing island shores.
Irregularly (crinkly) laminated ooids are a major sediment component over much of the platform interior and leeward margins in areas that receive frequent, but intermittent, wave and tidal agitation. These ooids occur in both broad shallow grainstone banks (0-2 m depth) and the deeper open platform (2-6 m depth).
Whereas Holocene ooids are commonly affected by biogenic degradation and are admixed with peloidal, grapestone, and/or skeletal grains, the widespread Pleistocene oolitic limestones are predominantly oolitic and have more strongly developed oolitic lamellae and less biogenic degradation. These Pleistocene ooids reflect higher energies associated with a more deeply flooded platform and less protection from marginal reefs and islands.
The widespread distribution of ooids on Caicos platform includes settings not normally associated with oolitic sand generation and provides an improved suite of models for reconstructing paleoenvironments of oolitic sand production and deposition.
AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.