LATE HOLOCENE RAISED SHORE PLATFORMS IN SOUTHWESTERN JAMAICA

We report a ¹⁴C age date of 1184–940 cal BP (95.4% CI) for a raised, serpulid-worm-encrusted shore platform, approximately 0.5–1.2 MASL, northwest of Billy's Bay in southwestern St. Elizabeth Parish, Jamaica. Raised shore platforms in this area indicate uplift along the Pond Side Fault. The platforms are composed of the White Limestone Group (mid-Eocene to mid-Miocene) and coral rudstone to floatstone and calcareous sandstone of the Coastal Group (late Pleistocene). Both units were beveled and subsequently encrusted with serpulid worm tubes, sessile bivalves, and vermiform gastropods that form an indurated coating up to 5 cm thick. The encrusted upper surfaces mostly are planar but some have elevated rims or complex networks of shallow tide pools. Rim material was sampled for the ¹⁴C analysis. The raised shore platforms are found below and adjacent to cliffs of the Coastal Group, where they are shore-attached or form discrete, isolated platforms that actively are being eroded. The closely spaced, isolated platforms generally are a few meters across and are irregular to quasi-circular in map view. A modern wave-cut notch has formed around the perimeters, and a few are deeply undercut, toppled, and at least two blocks have been overturned, transported, and deposited on top of the raised platform, presumably from high-energy storm surge. Documentation of neotectonic movement reinforces the ideas that the southwestern coast of Jamaica remains susceptible to seismic hazards, and that elevations on the Coastal Group are not reliable for accurate determinations of past stands of relative mean sea level.