The Sangamon-age Cockburn Town fossil coral reef complex displays a vertical sequence of facies from coral reef and closely associated subtidal carbonate sands, through beach calcarenites, to eolianites. This upward change reflects a progressive lowering of sea level and the eventual emergence of the reef complex into a subaerial environment. The contact between upper beach sediments and eolianites is at +4 m providing a minimum for the sea level high stand. Essentially in situ Acropora palmata suggests a sea level of at least 5 to 6 m above present. These values are similar to Sangamon-age high stands reported from New Providence, the northern Bahamas, and Bermuda.
Northerly flowing longshore currents deposited trough cross-bedded carbonate sands around and over coral heads, and this implies the existence of ancient San Salvador during development of the coral reef complex. Land lying to the east of the reef also is indicated by westerly dipping beach bedding. A large-scale, westerly dipping, tabular cross-bedded set of calcarenite records the effects on the Cockburn Town fossil reef of a major storm or hurricane.
The diagenetic sequence from submarine aragonite to freshwater vadose low-Mg calcite cements reflects the emergence of the reef complex and shows no evidence of subsequent immersion in marine waters. The sparsity of phreatic freshwater diagenetic effects may be due to a post-Sangamon rapid fall in sea level similar to that recorded for the same time on Bermuda, Calichification of all the facies of the reef complex and the development of rhizocretions resulted from extensive subaerial exposure and the growth of a vegetative cover respectively
