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

Abstract The Mayaguana and Caicos platforms are both located in the SE Bahamas. Caicos is one large edifice supporting small islands, whereas Mayaguana is smaller and comprises one island covering most of the bank surface. Providenciales (Caicos) 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, whereas reefal deposits are confined to the west coast. On this island, the older substrate consists of oolitic and bioclastic eolianites of middle Pleistocene age. On Mayaguana, oolitic ridges are subordinate to the reefs, and the oldest rock units include altered eolianites containing fragments of benthic foraminifers that became extinct in the Pliocene and fine-grained dolostone of possible middle Miocene age. This difference in the distribution of upper Pleistocene facies could be related to the extent of emerged land on platform tops or to the thickness of the water layer covering the latter during the last interglacial highstand. 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 eolian units on Mayaguana would question some fundamentals of Bahamian geology.