Middle Pleistocene reefs of northern Jamaica, and elsewhere in the Caribbean, are distinctly different from the late Pleistocene 120,000 year-old "Sangamon" reefs. They are more extensively developed, better lithified, and commonly dolomitized.

In Jamaica, the contact between the two units, the "Sangamon" Falmouth Formation and the middle Pleistocene "Yarmouth"(?) Hope Gate Formation, is erosional. This contact demonstrates that the diagenesis and dolomitization of the Hope Gate took place before Falmouth deposition. The Hope Gate dolomite replaces micrite and fills pores created by the dissolution of aragonite, demonstrating the near contemporaneity of aragonite solution and dolomite precipitation. The dolomites have low Sr (220 ppm) and Na (350 ppm) contents, precluding their precipitation from marine fluids.

Dolomitization took place as meteoric waters first infiltered the seaward growing, submarine-cemented reefs. The composition of the fluid from which the dolomite precipitated was controlled by the composition of the influxing meteoric water, but more significantly by the composition of the primary reef carbonate. Continued meteoric flushing, after the available Mg was consumed by dolomitization, resulted in low Na, low Sr, and C¹²- and O¹⁶-enriched calcites.

The vadose textures superimposed on the intense phreatic-meteoric diagenesis consists only of insignificant amounts of speleothems, despite more than 300,000 years of subareal exposure.

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