• The Swan Cay Member represents forereef deposits on a carbonate platform. (Coates et al, 2005; McNeil et al, 2013).

• The lower 15 m is exposed on the southerly low hill of the island and consists of silty sandstone and shelly calcarenitic siltstone, with coral rubble and red algal fragments and balls. The middle 4 m consists of calcarenitic clayey siltstone, with dense, fine shell-hash horizons, and abundant large coral colonies in the lower part. The upper 60 m of the formation consists of massively thick-bedded, pale tan-white limestone. The upper 30 m includes a 4-m-thick coral bed with large Montastraea colonies, other corals and mollusks. The lower 30 m contains silty calcarenite with common red algae and large foraminifera, shell hash, and micromollusks. Cave deposits, about 5 m above the base of the calcarenite, consist of silty, shelly, volcaniclastic sandstone, mixed with abundant volcanic cobbles and boulders, and calcareous reef rubble containing an abundant and diverse molluscan assemblage. The most abundant corals are Acropora palmata, A. cervicornis, Diploria labyrinthiformis, Montastraea faveolata, Porites furcata, Agaricia (Undaria) agaracites, Meandrina meandrites, and Dichocoenia stokesi. Organisms from a range of depths indicate that the deposit is reworked fore-reef debris formed at about 100 m (Collins et al., 1999; Coates et al., 2005).