Internal Hydrology and Geochemistry of Coral Reefs and Atoll Islands: Key to Diagenetic Variations

Abstract

Diagenetic changes in coral reef carbonates continue to generate both interest and controversy. Considerable attention has been devoted to carbonate porosity (Choquette and Pray 1970, Enos and Sawatsky 1981), pore-water geochemistry and diagenetic environments (Berner 1980, Longman 1980), and general geochemistry (Curtis 1977), but the subject of formation-scale fluxes and material balances has not received the attention it deserves. The rates, distributions, and mechanisms of fluid transport through the reef structure are basic to the understanding of diagenetic processes. Although some mineralogic transitions may be able to occur in a closed system (e.g., aragonite to calcite), others, such as dolomitization, require the passage of many volumes of pore water through the system in order to remove calcium and supply magnesium. Thus, the hydrogeology of a formation — porosity, permeability, the forces available to drive fluids through the system, and the evolution of these parameters over time — will exert important controls over the rate, nature, and extent of diagenesis. At the same time, diagenetic changes may provide important clues to formation hydrogeology and its development.