Miocene Reefs of Dominican Republic

Charles C. Evans

The Miocene-Pliocene Yaque Group of the Cibao Valley, Dominican Republic, contains several well-exposed examples of reef development and coral accumulation in a muddy, terrigenous shelf to slope sequence: an environment generally considered unsuitable for coral growth both because of the soft muddy bottom and the rapid siliciclastic input.

Coralline sediments in the Yaque Group occur as reefs, thickets, and coral debris, all three of which have a muddy, terrigenous matrix and are founded on muddy substrates. Reefs, 10-20 m thick, are limited to the more proximal portions of the shelf, at the limits of fining-upward and seaward trends. The reefs are overlain by conglomeratic strata. The stratigraphic setting of these reefs suggests that they have developed along the stalled portions of rapidly prograding fan deltas.

Thickets and layers of coral debris are found seaward and stratigraphically above the well-developed reef. The matrix sediments are exclusively fine-grained sand to mud, and the fauna are suggestive of more open shelf conditions. In thickets, branched (Porites spp., Pocillopora spp.), small massive (Montastrea spp., Siderastrea spp.), and foliose or platelike (Agaricia spp.) corals are found upright in the muddy sediment. Similarities in coral species and areal proximity suggest that thickets are the source of most layers of coralline debris. The association of coral debris with graded bedding and cross-bedding suggests that the coral debris has been reworked by storms.

The growth of corals and development of coral reefs in the Miocene-Pliocene Yaque Group is limited only by opportunities created by the slowing of siliciclastic sedimentation. Soft, muddy, terrigenous substrates and a continuing supply of terrigenous mud exert only a limited, indirect effect on reef growth.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.