ABSTRACT

Three major framework facies (algal pavement, coral heads, and branching corals) identified within the Holocene section of One Tree Reef show varying degrees of cementation. The widest distribution and greatest variety of submarine cements occur within those facies or subfacies that have extensive encrustation by coralline algae; these are found beneath the windward margin and within the patch reef drilled. Both Mg calcite and aragonite cements exhibit diverse fabrics and textures. Mg calcite is the dominant cement and is present as both an interskeletal and intraskeletal infill, whereas aragonite cement is exclusively intraskeletal. Interskeletal cements are relatively uncommon and are only developed within those facies or subfacies whose particular style of framework construction is capable of trapping significant quantities of fine-grained internal sediment.

Lithified crusts, with either a laminated or columnar morphology, are a prominent cavity infill within many of the reef framework facies. Although direct evidence is lacking at this stage, the morphology and other features of these crusts probably indicate some form of organic influence during their formation. Peloids, which are the major component of the lithified crusts as well as many other cavity infillings, are considered to be a particular form of Mg calcite micrite and to have nucleated within the interstitial waters of the reef. Microcrystalline rim cements around the peloids have often cemented them into a coherent mass that resembles detrital lime mudstones.