Beach-Swash Zone: Primary Ooid Factory?: ABSTRACT

Abstract

The shore of Long Bay along the southeastern coast of Providenciales Island in the Turks and Caicos Islands, British West Indies, represents a bankward-accreting beach and dune complex of Holocene oolitic grainstone. Offshore, en echelon bars of very low relief consist of skeletal-pelletal grainstones with thin oolitic coatings. Nearshore, the oolitic coatings become more numerous and thicker with the largest and most completely developed ooids found in the beach and swash-zone environments. Adjacent beach and storm-berm sands serve as the source for oolitic particles that have constructed dunes as much as 40 ft high. This observed relationship between ooids forming in the beach and swash zones, and their subsequent deposition in adjacent beach dunes may provide the most reasonable explanation for the topographically high oolitic dunes of Pleistocene age (some as high as 150 ft) that rim many of the narrow shelf margins of the Bahama Banks. In these settings, little evidence appears for extensive offshore bar development. It is possible, though difficult to prove, that production of oolitic coatings in Bahaman submarine tidal bars and banks (Cat Cay, Schooner Cays, south end of the Tongue of the Ocean) primarily occurs during periods of low tide in a beachlike environment rather than during periods of movement associated with strong tidal currents. This swash-zone method of oolite formation provides an alternative model to the traditional bar mechanism for the formation of elongate oolite sand accumulations. Such a mechanism might also explain extensive ancient oolitic sand sheets that may have grown through lateral accretion of the oolite-forming beach facies, or as a basal transgressive beach facies deposited during a relative sea level rise. End_of_Article - Last_Page 280------------