Turks and Caicos Basic Geology

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Regional Geology - Paleogeography, Tectonics and Climate

The Turks and Caicos Banks, as with the Bahamas, are interpreted to over lie continental crust that was rifted from the North American continental land mass when it separated from Northwest Africa during the break up of Pangea in the Triassic (Pindell, 1993). The Triassic sedimentary and volcanic section and earlier continental crust are interpreted, on the basis of the section in the Bahamas, to be buried beneath a cover of Jurassic, Cretaceous and Tertiary carbonate sediments.

During the Pleistocene, when glaciation sequestered ice over the Polar continental areas, sea level fell over 300 feet (100m). The banks would have been flat sub-aerial plateaus on which aeolian dune systems developed and, whose cliffed margins stood above the surrounding sea while kharstification caused the development of caves and blue holes. Some of the most striking caves are found on Middle Caicos. These are believed by some to host the largest cave network of the Bahamian island chain.

The northern margin of the Caicos Platform experiences the oceanic swells from the open Atlantic (Wanless and Dravis 1989) generated by the easterly trade winds which drive the westward-flowing Antilles Current. The climate is subarid, so all but the larger islands receive less than 70 cm of rainfall per year (Milliman, 1966). Most of the rainfall is associated with convection over the larger islands. Smaller islands, which include West Caicos, receive much less rainfall. Evaporation far exceeds rainfall, and brines and evaporites form in coastal salinas and tidal flats. As Wanless and Dravis (1989) point out the brines may influence both surficial and subsurface settings and there is no major source of groundwater or surficial freshwater on Caicos Platform.
From a geologic perspective interestingly Caicos Platform lies directly in the Caribbean hurricane corridor and is affected by hurricane force winds on the average of once every 5.5 years (Neumann et al., 1978), somewhat more frequently than Florida. Hurricanes dominate the sedimentation and character of the sediment body geometries and their sedimentary structures, including exotic tempestites. Wanless and Dravis (1989) describe how the last two major hurricanes to affect Caicos Platform were Kate in November of 1985, with winds of 145-175 km/hr (90-105 mph), and Donna in September of 1960 with winds of 250 km/hr (150 mph). Although hurricanes can produce a variety of wind driven sequences, westward-moving storms tend to produce northerly winds prior to passage of the storm and southerly winds following storm passage.

Shallow depressions in the limestone form lagoons whose waters evaporate and forming brines that precipitate seasonal evaporites, including gypsum, calcium carbonate, and halite. These salinas, similar to those now found on West Caicos, attracted salt "rakers" from Bermuda in the 17th century. These seasonal laborers became permanent settlers and formed the basis of the salt industry which lasted into the mid-20th century.

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Friday, March 29, 2013