THE USE OF DIAGNOSTIC CORALS AND FORAMINIFERA TO RECONSTRUCT THE DEPOSITIONAL HISTORY OF THE MIOCENE TO PLIOCENE MONA REEF COMPLEX, PUERTO RICO

The Miocene to Pliocene Mona Reef complex located in Isla de Mona, Puerto Rico was investigated to define facies distribution, identify corals, describe strata geometries, and provide insights in the depositional history of the platform. The Isla de Mona Reef complex was well established by Middle Miocene Based on the available ⁸⁷Sr/⁸⁶Sr values that indicates Serravallian ages for the earliest dolomitization on the platform. Although diagenetic overprinting precluded the use of ⁸⁷Sr/⁸⁶Sr to constrain depositional ages, corals and foraminifera species were useful for making age estimation and depositional environmental interpretations. The common biotic components in Isla de Mona are corals, benthic foraminifera, red algae, echinoids and bryozoans and the dominant benthic foraminifera genera in the platform are the Amphistegina. At least 31 scleractinian coral species were identified, while the dominant species are Stylophora minor, Caulastrea portoricencis and Acropora cervicornis. The stratigraphy of the Isla de Mona carbonate platform was divided into two major units that are separated by an island wide unconformity: Unit I encompasses a Miocene coral reef framework and Unit II a Pliocene coral reef framework. The Miocene to Pliocene boundary on Isla de Mona is characterized by the demise of the Stylophora reef complex and the formation of the Miocene to Pliocene unconformity. During the Pliocene the coral Acropora cervicornis colonized the platform resulting in the stabilization of the Acropora cervicornis reef complex over the unconformity. In order to reconstruct the depositional history of the platform a new depositional model for the Isla de Mona Reef Complex was proposed. The model is characterized by six stages that were developed in relation to relative sea-level fluctuations. In addition the model was subdivided in 14 distinct facies based on lithology and skeletal components; the facies represents six depositional environments: distal platform, proximal platform, reef core, patch reef, reef slope and open shelf.