Pre-Holocene Island Geology of the Caicos and Mayaguana (Bahamas) Platforms: Similarities and Differences

Pascal F. Kindler¹, Fabienne Godefroid¹, and Elias Samankassou^2
1Department of Geology, University of Geneva, Geneva, Switzerland
²Department of Geosciences, University of Fribourg, Fribourg, Switzerland

Preliminary geological investigations on Providenciales (Caicos) and Mayaguana (Bahamas) show disparities between the two islands, possibly related to differences in the area of emerged land on platform tops.

The Mayaguana and Caicos platforms are located in the SE Bahamas. Caicos is a large (100x70 km) edifice supporting small islands along its northern margin. Mayaguana is smaller (55x15 km) and comprises one island covering most of the platform surface. Providenciales and Mayaguana islands predominantly consist, in different proportion, of reefal framestones and oolitic grainstones dating from the last interglacial period. Oolitic ridges are widely exposed on Providenciales where reefal deposits are confined to the west coast. In Mayaguana, oolitic ridges are subordinate to the reefs that occur along most of the island shorelines. In Providenciales, the older substrate consists of oolitic and bioclastic eolianites of middle Pleistocene age. In Mayaguana, oldest rock units include fine-grained dolostone and bioturbated marine facies, exposed at about +8 m, containing fragments of benthic foraminifers that became extinct in the Pliocene.

This difference in the distribution of Pleistocene facies could be related to the extent of emerged land on platform tops. The Caicos physiography was favourable to water circulation and thus to ooid production on the platform. By contrast, the setting in Mayaguana was more conducive to reef growth. The oolitic and bioclastic substrates exposed on Providenciales are similar to those observed in the northern Bahamas. If confirmed, the pre-Quaternary age of the dolomitic and elevated marine units on Mayaguana would question some fundamentals of Bahamian geology.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas