GEOLOGY OF THE COASTAL GROUP, WESTERN ST. ELIZABETH PARISH, JAMAICA

The Coastal Group, which includes various limestone, dolomite, and clastic strata, has not been studied in detail in southwestern Jamaica. Studies in the north and southeast coasts of Jamaica have interpreted the upper Coastal Group as having accumulated, in part, during the marine isotope stage (MIS) 5e, which corresponds to the Eemian interglacial. This study addresses: 1) the distribution of the Coastal Group in southwestern Jamaica, 2) sequence stratigraphy of this interval, 3) ages of fossil reefs in the succession, and 4) the response of stable isotopes recorded within this interval. Within this context, this study proposes to test the hypothesis that the deposition of the Coastal Group carbonates coincided with the MIS 5e. Nine vertical sections were measured, described, and sampled along a 1.8 km long northeast-southwest-trending transect between the west end of Billy Bay and Black Springs Point, where the Coastal Group is nearly continuously exposed. Thicknesses of the measured sections ranged from 7-10 meters. The vertical cliffs contain multiple facies transitions that are occasionally associated with sharp unconformities. These facies transitions also show offlapping packages of mixed carbonates and siliciclastics toward the southeast along strike. Common facies observed include skeletal wackestone, carbonate-rich quartz sandstone containing shell fragments, corals and conchs, coral cobble to boulder rudstone with a skeletal grainstone matrix, skeletal grainstone, and carbonate-rich quartz sandstone containing bioclasts. Some notable corals found within the coral cobble-boulder rudstone unit include Acropora palmata, Acropora cervicornis, Colpophyllia natans, Diploria spp., and Porites spp. with some of these coral heads appearing to be preserved in situ.