Date of Award
Master of Science
Geological and Environmental Sciences
Dr. Stephen E. Kaczmarek
Dr. Peter Voice
Dr. Andrew Caruthers
Dolomite, dolomitization, salinity, molarity, stoichiometry
Masters Thesis-Open Access
Numerous environmental factors affect dolomitization. Shallow peritidal and restricted marine environments, for example, are often associated with more abundant and more stoichiometric dolomite than deeper marine environments. Higher fluid Mg/Ca ratios resulting from gypsum precipitation are often invoked to explain this observation, even when evidence of evaporites is absent. In this study, high-temperature dolomitization experiments show that the concentrations of major cation concentrations (Na, K, Mg, and Ca) impact dolomite stoichiometry and reaction rate. Nearly 200 batch dolomitization experiments were run whereby 100 mg of natural aragonite ooids were dolomitized at 215°C in ionic solutions. Fluid [NaCl] and [KCl] correlate positively with the stoichiometry of the initial protodolomite product (43–48 mol% MgCO3), but negatively with reaction rate. In contrast, the [Mg] and [Ca] of the dolomitizing fluid correlate positively with both reaction rate and protodolomite stoichiometry (41–45 mol% MgCO3). The rate at which cation ordering develops is unaffected by [NaCl], [KCl], [Mg], or [Ca] in the dolomitizing fluid. These findings provide the basis for an alternative explanation for the observed relationship between restricted, peri-tidal marine carbonate facies and higher dolomite abundance and stoichiometry without the need to invoke precipitation of calcium-bearing evaporites. These observations add to our understanding of the fundamental controls on dolomite stoichiometry and reaction rate, and can help further constrain geological interpretations based on dolomite stoichiometry.
Cohen, Hanna F., "Evaluating the Effects of Sodium, Potassium, Magnesium, and Calcium Concentrations on Dolomite Stoichiometry, Cation Ordering, and Reaction Rate" (2019). Master's Theses. 5096.