The origin of common dolomite fabrics; clues from the Pliocene

Features common to dolomites of all ages in Pliocene dolomites from the Netherlands Antilles. These include pseudomorphic replacement, selective replacement, fossil moldic porosity, cloudy-centered, clear-rimmed dolomite, sucrosic dolomite, and dolomite cement. Development of these features is controlled by mineralogy of the material being replaced, saturation of the bulk solution with respect to the mineral being replaced, and availability of dolomite nucleation sites. Low-Mg calcite (LMC) was often neither replaced by dolomite nor dissolved but aragonite and high-Mg calcite (HMC) were both replaced and dissolved. Resistence of LMC to dolomitization was due to solutions saturated was LMC and the lack of nucleation sites. Cryptocrystalline LMC was more readily replaced because it provides more nucleation sites. Cloudy-centered, clear-rimmed dolomite and sucrosic dolomite formed in sediments with abundant LMC and few nucleation sites. Fossil moldic porosity developed concurrent with pseudomorphic replacement, suggesting that the solution was undersaturated. Dolomite cement commonly lines pores and fills intraparticle pore space, and its crystals are larger than replacement crystals because there are fewer nucleation sites.--Modified journal abstract.