Recent sedimentary facies of isolated carbonate platforms, Belize-Yucatan System, Central America

Distribution of recent sedimentary facies is significantly different in fou r closely spaced, isolated carbonate platforms off the coasts of Belize and Yucatan (SE Mexico), These differences are largely controlled by variation s in submarine topography, which are likely the result of differential subs idence and karstification from platform to platform, A variety of depositio nal styles and patterns is found in platform interiors that developed durin g the same Holocene sea-level rise, Composition and texture of surface sedi ment samples were used to define four major sediment types and to distingui sh nine depositional environments within the platforms, Facies maps are bas ed on analysis of 454 sediment samples and high-resolution satellite imager y. Glovers Reef is characterized by a circular facies distribution. The nearly continuous reef margin is composed of a coral-red coralline algae-Halimeda grainstone. Mixed nonskeletal (peloidal)/skeletal wackestones and packston es are present in shallow lagoon parts (< 5 m water depth) behind the margi n. The deep interior, from 5 to 18 m mater depth, is characterized by mollu sk-foram-Halimeda wackestones with over 860 patch reefs of coral-red algae- Halimeda-mollusk packstones, Lighthouse Reef also has a coral grainstone an d coral-red algae-Halimeda grainstone rim, but the facies distribution in t he interior is strongly asymmetrical. The 8-m-deep eastern lagoon is floore d by mollusk-foram-Halimeda wackestones and packstones; the 3-m-deep wester n lagoon has the mixed peloidal/skeletal wackestone to grainstone facies, A linear trend of coalescing patch reefs and skeletal grainstone facies sepa rates the two lagoons, Banco Chinchorro is similar to Lighthouse Reef, inas much as facies distribution patterns of the interior are strongly asymmetri cal. Mallusk-foram-Halimeda wackestones-grainstones are present in eastern lagoon areas, whereas shal low (< 5 m) western parts of the lagoon are comp osed of mixed peloidal/skeletal grainstones, packstones, and wackestones. M ost of Turneffe Islands is protected on the east by Lighthouse Reef. Accord ingly, Turneffe has a narrower reef and skeletal grainstone rim than the ot her two platforms. Restricted interior lagoons are up to 8 m deep, and are enclosed by wide mangrove rims and surface sediments dominated by Halimeda- rich wackestone rich in organic matter. Coral patch reefs are absent. In co ntrast, the unprotected northernmost part of Turneffe has a wide reef and g rainstone rim and the open lagoon area consists of mollusk-foram-Halimeda w ackestones-packstones with abundant patch reefs.