Textural and geochemical alternations in Late Cenozoic Bahamian dolomites

Dolomitized intervals of a core from San Salvador Island, Bahamas, exhibit variations of two texturally and geochemically distinct end‐members. In the Pliocene section of the dolomitized interval, the two end‐members alternate in a pattern that may reflect originally and/or diagenetically modified depositional facies. Formerly mud‐free intervals, locally capped by exposure surfaces are massive crystalline, mimetic dolomites (CM). Muddier sediments are replaced by friable microsucrosic dolomites (MS). CM and MS dolomites also differ in porosity (< 10% vs > 30%), permeability (< 10 md vs > 100 md), mol% MgCO₃ (44–9 vs 47–7) mol%), oxygen isotopic composition (1–7 vs 2–7‰) and strontium content (241 vs 106 ppm). These data indicate that depositional and diagenetic fabric are the principal controls governing the distribution of dolomite types. Differences in texture and geochemistry are suggested as arising through differential rates of crystallization produced as a result of variations in permeability and reactivity of the precursor sediments and rocks.