A fluid inclusions study of Puerto Rico tertiary dolomite

Abstract

The north coast Tertiary limestone of Puerto Rico is composed of carbonate rocks that contain the most important aquifer in Puerto Rico. The dolomites of the north coast of Puerto Rico have been studied by González and Ruiz, (1991) by Ramírez, (2000). Both studies suggest mixing zone dolomitization for these dolomites. This study is based on the study of fluid inclusions analysis in the Puerto Rico north coast dolomites to better constrain in environment of precipitation. Fluid inclusions analysis provides direct information on the environments and the temperatures of precipitation. The samples of dolomites analyzed are from the Montebello Member at the Cibao Formations and the Lares Limestone. The temperatures obtained for the fluid inclusions present in Montebello Member at Cibao Formation at depth (510.1) and (420.1) are 0.0 and 0.1 at depth (510.1) that show a small quantity of salt in the samples. Fluid inclusions can be trapped during the process of recrystallization in diagenetic minerals. The inclusions that are present during the process of recrystallization provide the record of the conditions of recrystallization rather that the original precipitation of the mineral. The inclusions in north coast of Puerto Rico indicated the alterations of dolomites in fresh water environments and small quantity of salts zone where the dolomites have been precipitated meteoric-marine mixing zone. Stable isotopic analysis in the same samples was made to help identify the environments of precipitation. The stable isotopic analysis in Garrochales at Barceloneta Quadrangle, Manatí Quadrangle and Lares Limestone and Montebello Member at the Cibao Formation cores indicated alterations in meteoric and marine water.