Date of Award

12-2019

Degree Name

Master of Science

Department

Geological and Environmental Sciences

Department

Geosciences

First Advisor

Dr. Stephen E. Kaczmarek

Second Advisor

Dr. Peter Voice

Third Advisor

Dr. Andrew Caruthers

Keywords

Dolomite, dolomitization, salinity, molarity, stoichiometry

Access Setting

Masters Thesis-Open Access

Abstract

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.

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