Relationship between Dolomite Nonstoichiometry and Carbonate Facies Parameters
David N. Lumsden, John S. Chimahusky, 1980. "Relationship between Dolomite Nonstoichiometry and Carbonate Facies Parameters", Concepts and Models of Dolomitization, Donald H. Zenger, John B. Dunham, Raymond L. Ethington
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Two hundred ninety carbonate rock samples from nearly all pre-Cenozoic periods, from widely scattered North American sites, representing all of Dunham's carbonate rock types, and containing 5%–100% ordered dolomite in the carbonate fraction were analyzed for a possible relationship between dolomite nonstoichiometry (expressed as mole percent CaCO3) and pétrographie parameters and stratigraphie position. Dolomite composition ranged from 49.3 to 57.3 mole percent CaCO3, with modes from 50.0% to 52.0% and 54.0% to 56.0%. Data indicate that dolomite nonstoichiometry is not related to insoluble residue, porosity, rock type, percentage of crinoid fragments, recrystallization (dolomite crystal size), and percentage of dolomite in the carbonate fraction in dolomitized limestones. A general trend toward more nearly stoichiometric composition with age is obscured by local effects. Crystalline dolomites tend to be more nearly stoichiometric and less variable in composition (mode 50.0%–51.0% CaCO3) relative to dolomicrites (modes 51.0%–52.0% evaporitic; 54.0%–55.0% nonevaporitic) and dolomitized lime mudstones (modes 51.0%–52.0% evaporitic; 55.0%–56.0% nonevaporitic). Evaporite-related dolomite is almost invariable near stoichiometric or calcium depleted. Open-marine and stoichiometric, evaporite-related dolomites are products of syndepositional dolomitization; nonstoichiometric nonevaporite dolomite is syndepositional to early diagenetic; and crystalline dolomite is middle to late diagenetic.
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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.