Factors Controlling Sediment Preservation on a North Jamaican Fringing Reef: A Process-Based Approach to Microfacies Analysis

Compositional characteristics of limestones are fundamental to the interpretation of depositional environments, with an assumption that preserved grain assemblages preserve sufficient evidence of initial sediment input to enable delineation of environments. It is acknowledged, however, that a range of early diagenetic processes (including encrustation, fragmentation, abrasion, microboring, dissolution, cementation, and recrystallization) may influence grain preservation potential, and thus bias the composition of resultant grain assemblages. This study examines the effects and relative importance of a range of early diagenetic processes across a fringing reef at Discovery Bay, north Jamaica. Physical processes (abrasion and fragmentation) are most important at shallow fore-reef sites, whilst back-reef sites are dominated by biochemical processes, including microboring, recrystallization, biofilm-related calcification, and dissolution. Grain susceptibility to each process is highly variable and influenced by mineralogy and skeletal structure. Coral fragments, for example, are most susceptible to the effects of microboring, whereas Halimeda plates are most susceptible to dissolution. Extensive alteration of grain assemblages is predicted within the back-reef, where dissolution of coral and Halimeda occurs because of intense microboring and pore-water undersaturation. Fore-reef assemblages, by contrast, remain relatively unaltered. Results have implications both for improved ecological interpretation of carbonate sedimentary sequences and for understanding of how and why carbonate microfacies develop.