Experimental studies of the kinetics of reaction of calcium carbonate with magnesium-calcium chloride solutions indicate a solution-reprecipitation mechanism with a cation-ordered protodolomite as the initial reaction product. Nucleation of ordered dolomite is extremely difficult at low temperatures and is an important factor in the reaction. The kinetics of the reaction are strongly dependent on temperature and on the reactant (calcite or aragonite). Experimental dolomitization of aragonite at 100°C and atmospheric pressure has allowed the reaction to be studied under conditions approaching those of natural sedimentary environments. These studies indicate that other important kinetic factors include the ionic strength (salinity) and Mg++/Ca++ ratio in the dolomitizing fluids and the presence of strongly hydrated ions. Certain amino acids and soluble proteins severely inhibit the reaction, but may be removed by oxidation. The results of these experiments may aid in the interpretation of the processes involved in sedimentary dolomitization.
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Special Publication 28 has its roots in the 22nd Annual Research Symposium of SEPM entitled Concepts and Models of Dolomitization – Their Intricacies and Significance held on April 3,1979 in Houston, Texas as part of the joint annual meetings of AAPG and SEPM. The purpose of that symposium was to express the state-of-the-art of the study of the elusive process(es) of dolomitization. Most of the contributions in this volume are concerned with apparent early, nearsurface dolomitization, either by hypersaline brines, by the marine-meteoric mixing model or some variant thereof, or by both mechanisms where more than one phase or kind of dolomite exists, or where the origin of a particular dolomite is uncertain. Other models and aspects of dolomitization are treated here as well.