CAVES FORMED IN CENOZOIC ISLAND DOLOMITE OF THE CARIBBEAN

Dolomite formation on carbonate islands is constrained by: young island age, limited island area, and available dolomitizing mechanisms. Another constraint is the presence of dissolutional caves. To understand the history of dolomite formation and karst formation on dolomite, three island dolomites were investigated: dolomitized sections of chalk from the Miocene Oceanics Group of Barbados, dolomitized Neogene reef deposits on Curacao, and dolomitized Mio-Pliocene reef limestone on Isla de Mona. These dolomitic units range in textures from mimetic-replacive to non-mimetic, fabric-destructive.

Photo-documentation and detailed surveys of caves formed within dolomite were performed to compare morphologies to flank margin caves and sea caves. Rock samples of the cave wall, as well as samples above and below the caves, were taken to confirm that the caves were formed completely within dolomite. On Isla de Mona, vertical transects were performed to determine if any spatial relationships between cave formation and overlying lithology exist. Selected thin-section and geochemical analyses, such as XRD and stable isotope analysis, are on-going.

On Barbados, the dolomitized chalk contained several dissolutional caves; non-dolomitized sections of chalk lacked caves. On Curacao, several caves were documented completely within dolomitized back-reef facies. On Isla de Mona, well-developed flank margin caves were found at the contact between two carbonate units, the Isla de Mona Dolomite and the Lirio Limestone. Ten caves were documented completely within the dolomite. Most of these caves were highly eroded due to cliff retreat; however, two caves were almost completely intact, with the morphology of flank margin caves. Documentation of dissolutional caves on island dolomites provides an additional constraint on the formation of island dolomites. The spatial and temporal relationship between dolomite and associated karst features introduces another perspective to the dolomite problem. If dolomitization is post-void formation, then subaerial exposure had already occurred, resulting in the development of a freshwater lens; and large scale porosity, such as caves, can survive dolomitization. If the dolomitization is pre-void development, then flank margin caves form in dolomite as in limestone.