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

Distribution of recent sedimentary facies is significantly
different in four closely spaced, isolated carbonate platforms off the
coasts of Belize and Yucatan (SE Mexico). These differences are
largely controlled by variations in submarine topography, which are
likely the result of differential subsidence and karstification from
platform to platform. A variety of depositional styles and patterns is
found in platform interiors that developed during the same Holocene
sea-level rise. Composition and texture of surface sediment samples
were used to define four major sediment types and to distinguish nine
depositional environments within the platforms. Facies maps are based
on analysis of 454 sediment samples and high-resolution satellite
imagery. 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 packstones are present in shallow
lagoon parts (< 5 m water depth) behind the margin. The deep interior,
from 5 to 18 m water depth, is characterized by
mollusk--foram--Halimeda wackestones with over 860 patch reefs of
coral--red algae--Halimeda--mollusk packstones. Lighthouse Reef also
has a coral grainstone and coral--red algae--Halimeda grainstone rim,
but the facies distribution in the interior is strongly
asymmetrical. The 8-m-deep eastern lagoon is floored by
mollusk--foram--Halimeda wackestones and packstones; the 3-m-deep
western lagoon has the mixed peloidal/skeletal wackestone to
grainstone facies. A linear trend of coalescing patch reefs and
skeletal grainstone facies separates the two lagoons. Banco Chinchorro
is similar to Lighthouse Reef, inasmuch as facies distribution
patterns of the interior are strongly
asymmetrical. Mollusk--foram--Halimeda wackestones--grainstones are
present in eastern lagoon areas, whereas shallow (< 5 m) western parts
of the lagoon are composed of mixed peloidal/skeletal grainstones,
packstones, and wackestones. Most of Turneffe Islands is protected on
the east by Lighthouse Reef. Accordingly, Turneffe has a narrower reef
and skeletal grainstone rim than the other 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 contrast, the
unprotected northernmost part of Turneffe has a wide reef and
grainstone rim and the open lagoon area consists of
mollusk--foram--Halimeda wackestones--packstones with abundant patch
reefs.