A continuous 168-m core was collected on San Salvador in the eastern Bahamas. Dolomite is present in the interval between 35 and 147 m. The dolomite is of 2 basic lithologic types. Those dolomites which are probably supratidal mudstones and show laminations, a poorly developed fauna, a few intraformational clasts, and in places a capping red crust, are termed "stratal" dolomites. These stratal sequences are less than 10 cm thick. Those dolomites which are replacements of grain-supported carbonate sediments or rocks, probably of backreef or lagoonal facies, are termed "massive" dolomites.

Stable isotope analyses show both types of dolomite to have ^dgrC¹³ values within the range of Holocene sediments, but to be higher in ^dgrO¹⁸ than either Holocene sediments or Pleistocene limestones. These data indicate the dolomites formed by reaction of host carbonate sediments or rock with Mg-rich hypersaline brines. The stratal sequences were probably dolomitized by upward capillary movement of the fluids, whereas the massive sequences were dolomitized by seepage refluxion. Stratal dolomites seem to be relatively lower in ^dgrO¹⁸ and mol % MgCO₃ and more poorly ordered than massive dolomites. This may reflect different efficiencies of the 2 dolomitization processes.

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