The upper Pleistocene Falmouth Formation of Jamaica was deposited in shallow, open-marine environments similar to those on the modern northern shelf. Depositional facies include coralgal boundstones, coral-algal grainstones, foram-algal packstones, echinoid molluscan wackestones, and terrigenous grainstones. Submarine cementation of Falmouth sediments occurred as micritic and/or isopachous bladed rinds composed of magnesian calcite, as well as aragonitic coral overgrowths. The Falmouth limestones were subsequently exposed to meteoric water because of eustatic sea level fall and regional tectonic tilting related to the Cayman shear zone to the north. Isotopic reequilibration and carbonate-mineral stabilization are presently at an intermediate stage. Meteoric and mixing-zon diagenetic processes that have affected this unit include: sparry calcite cementation, aragonite dissolution and inversion, incongruent dissolution of high-magnesian calcite, selective dolomitization, and neomorphism of micritic matrices. Neomorphic fabrics within the Falmouth are spherulitic sparry calcite, microspar, and structure grumuleuse. Isotopic reequilibration coincides with the degree of diagenetic alteration. Carbon and oxygen delta values are lighter in precipitative meteoric cements than in neomorphic constituents. The trend toward negative isotopic composition with increasing age of limestone strata can be shown here to be disguised by exposure to sea spray, organic involvement, and abnormally rapid (nonequilibrium) rates of precipitation. Modern subsurface hydrogeologic e vironments contain distinctive diagenetic fabrics and isotopic signatures, and are defined by water-flow rate, pore-water chemistry, and rock permeability and porosity.

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