Fabrics and sequences of submarine carbonate cements in Holocene Bermuda cup reefs

A variety of precipitative synsedimentary CaCO₃ cements lines or fills cavities and surrounds sediment particles within Recent algal cup reefs which dot the rim of the Bermuda platform. These include aragonite needle, spherulitic, and lath cements as well as calcite micrite, palisade, scale, and blocky cements, listed according to respective relative abundances. No distribution pattern of cements is apparent; various combinations of three or four cements are found in almost every sample or thin section. From the occurrence of various cements, factors determining composition and fabric are deduced:

1. Morphology, composition, and coating of the substrate.
2. Direct or indirect influence of organisms such as algae, pelecypods, or crustaceans.
3. Micro-environment, specifically size and permeability, rate of sea-water circulation through the micro-environment, substrates and organisms within the microenvironment.

Various sequences of two or three precipitative cements result from changes in microenvironment; the only cause of such change recognized is the entrance of endolithic algae into partly cemented cavities. This study provides some insight into the origin of submarine cements and a basis for comparative interpretation of cements in fossil marine environments, especially fossil reefs.