ABSTRACT

Characteristic features common to dolomites of all ages are found in Pliocene dolomites from the Netherlands Antilles. These features include 1) pseudomorphic replacement, 2) selective replacement, 3) fossil moldic porosity, 4) cloudy-centered, clear-rimmed dolomite, 5) sucrosic dolomite, and 6) dolomite cement. The development of a particular feature is controlled by 1) mineralogy of the material being replaced, 2) the degree of saturation of the bulk solution with respect to the mineral being replaced, and 3) the availability of dolomite nucleation sites.

Low-Mg calcite (LMC) cement and fossils were often neither replaced by dolomite nor dissolved but aragonite and high-Mg calcite (HMC) were both replaced and dissolved. The resistence of LMC to dolomitization was due to solutions saturated with respect to LMC and the lack of nucleation sites. Cryptocrystalline LMC was more readily replaced by dolomite 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 dolomitizing solution was undersaturated with respect to the mineral being replaced.

Dolomite cement commonly lines pores and fills intraparticle pore space. Dolomite cement occasionally has inclusions of a precursor LMC cement. Dolomite cement crystals are larger than replacement crystals because there are fewer nucleation sites for the cement crystals.