Pleistocene Reefal and Oolitic Core Sequences from West Caicos, Caicos Platform
Shallow core boring transects on West Caicos record the late Pleistocene evolution of the leeward margin of Caicos Platform. Through the Pleistocene and Holocene, the leeward margin has progressively evolved from an open margin to one blocked by emergent topography, resulting in a dramatic shift in facies.
A leeward margin barrier reef, formed behind the protection of emergent topography (oolitic grainstone ridges) has persisted through the last two Pleistocene and the Holocene interglacial high stands. Soil crusts define emergent periods. The youngest interglacial produced a classic shallowing upwards reef barrier which built to a reef flat about 4 meters above present sea level. Older Pleistocene units are increasingly recrystallized and cemented, but the youngest retains most of the depositional mineralogy and has little marine or freshwater cement. Pleistocene and Holocene reef sequences are each capped by oolitic grainstones spread across the reefs by longshore advancing beach spit accretion from ooid sources to the north and south. Ooid smothering of reef sequences occurs as a later part of each sea level high stand.
Where not protected by emergent topography, the Pleistocene leeward margin sequence is repeated shallowing-upwards, burrowed to layered oolitic grainstone sequences. These grainstones retain much of their depositional mineralogy and are only weakly cemented. Well-cemented soil crusts, formed during sea level low stands, separate marine sequences and form permeability barriers that are responsible for ponding of brines from overlying Holocene salinas and defining areas of dolomitization.
AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas