Evaluating the Effects of Sodium, Potassium, Magnesium, and Calcium Concentrations on Dolomite Stoichiometry, Cation Ordering, and Reaction Rate

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Evaluating the Effects of Sodium, Potassium, Magnesium, and Calcium Concentrations on Dolomite Stoichiometry, Cation Ordering, and Reaction Rate, Is A Well-Researched Topic, It Is To Be Used As A Guide Or Framework For Your Research.

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 resultingfrom 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.

TABLE OF CONTENTS

ACKNOWLEDGEMENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF EQUATIONS
CHAPTER
I. INTRODUCTION…………………………………………………………………….1
Dolomite ……………………………………………………………………..……..1
Research Question ………………………………………………………………….4
II. LITERATURE REVIEW …………………………………………………………….6
Fluid Chemistry …………………………………………………………………….6
High Temperature Experimental Work …………………………………………….8
III. METHODS …………………………………………………………………………..11
Experimental Procedure ……………………………………………….………..11
Analytical Techniques …………………………………………………………..15
IV. RESULTS …………………………………………………………………………….17
Replacement Reaction ……………………………………………….………….17
Protodolomite Reaction Rate ……………………………………………………..20
Protodolomite Stoichiometry …………………………………………….………22
Dolomite Cation Ordering ………………………………………………………..24
V. DISCUSSION AND CONCLUSIONS ……………………………………………..26
Comparison to Previous Work ……………………………………………….…26
Reaction Curve ……………………………………………………….…26

Rate of Dolomitization (Protodolomite) …………………………………27
Ooid Size ……………………………………………………..…..………28
Calcite Dolomitization………………………………………….………..28
Mechanisms for Salt Influence ………………………………………………….29
Implications ………………………………………………………………………32
Dolomite as a Proxy for Understanding Fluid Chemistry ……………………32
Global Correlations …………………………………………………………..35
Conclusions ………………………………………………………………………36
REFERENCES ………………………………………………………………………..…………38
APPENDIX
A. Dataset ………….……………………………………………………..……….………… 45
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Additional information

Author

Hanna F. Cohen

No of Chapters

5

No of Pages

81

Reference

YES

Format

PDF

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