Contemporary subsea cementation is restricted to specific zones in shallow British Honduras barrier and atoll reefs. On the southern half of the barrier reef and on Glovers Atoll, cementation occurs only on the seaward margins of the reefs, the reef flat, and spur and groove structure.

On the reef flat, coral rubble and skeletal sand are cemented to a hard pavement 10-100 m wide. Coral fronds from the pavement have a radiocarbon age of about 450 years B.P. The cores of projecting spurs, a growth frame of coral and Millepora, locally are bound with a mortar of cemented skeletal sand, forming marble-hard limestone. Coral fronds lying loose on groove floors between spurs contain well-cemented geopetals, indicating lithification of internal sediment in place.

Carbonate cement is present (1) in intraskeletal voids of reef-building organisms, (2) between skeletal sand grains that form the rubble mortar and that partly fill the growth frame, and (3) within fine skeletal sand and carbonate mud geopetals of mollusk and sponge borings.

The localization of subsea cementation on the reef flat and seaward faces of the British Honduras marginal reefs significantly enhances their wave resistance. A similar localization of early cementation by magnesium-calcite in ancient reef complexes would have reduced porosity and permeability and increased the amount of magnesium locally available for dolomitization. This facies-specific diagenesis would have directed subsequent subaerial and late diagenesis, which in turn determines the quality of reef reservoirs.

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