Distribution of Submarine Cements in a Modern Caribbean Fringing Reef, Galeta Point, Panama

Abstract

ABSTRACT Petrographic characteristics and distribution of submarine cements vary considerably throughout a section of a modern reef off Galeta Point, Panama, as disclosed by cores from thirteen drill holes up to 14 m deep. Core holes were closely spaced along two transect lines which, when combined, extend from inshore mangroves to the outer reef slope of this Caribbean fringing reef. The submarine cement is predominantly dense, submicrocrystalline-microcrystalline to porous, submicrosucrosic magnesium calcite (15 to 19 mole percent MgCO3), with minor amounts of acicular aragonite. Magnesium calcite coats, infills and forms a matrix around various reef components, whereas aragonite is generally restricted to rim cement in skeletal cavities of corals. Variations in concentration and type of submarine lithification are not related to depth in Galeta reef. Rather, submarine cementation appears to be a relatively near-surface phenomenon most prevalent in sedimentological units (facies) of the reef which were formed under conditions of high agitation and/or slow accumulation. Therefore, well-developed cement crusts and infilled rims of the Acropora palmata facies, formed under high agitation but also at a rapid rate of accumulation, grade into dense matrix cement in the agglomerate limestone of the slower accreting fore-reef pavement facies and in the extensively bored and filled corals of the coral-head facies in the fore reef. Cements are absent or generally poorly developed in the deeper fore-reef talus or in protected reef-f at rubble and back-reef sediments.