Calcite rafts, peloids, and micrite in cave deposits from Cayman Brae, British West Indies

Speleothemic deposits from the Oligocene–Miocene Bluff Formation of Cayman Brae include calcite rafts that formed in cave pools. The rafts, which formed at the surface of the cave pools where rapid degassing of CO2 from the surface waters led to the precipitation of the calcite, can be divided into single- or double-sided spar calcite rafts and symmetrical, asymmetrical, or composite micrite – spar calcite rafts. Agitation of the water caused the rafts to sink and accumulate on the floor of the pool.Cavities formed by stacking of the calcite rafts are filled or partly filled with spar calcite, micrite, peloids, and terra rossa glaebules. The micrite laminae, like those in the micrite – spar calcite rafts, probably formed through the merger of peloids, which are formed of either subhedral to euhedral crystals or anhedral to subhedral grains. Available petrographic evidence suggests that the micrite and the peloids formed by precipitation from cave water. This example demonstrates that high-magnesium calcite peloids are not necessarily indicative of early marine diagenesis in reefs.