Variations in Mg/Ca as a Control on Distribution of Strontium Concentrations and δ¹⁸O in Upper Tertiary Dolomites from Bahamas: ABSTRACT Free

Strontium concentrations and δ¹⁸O are commonly used to infer the gross composition of dolomitizing waters, yet the bases for such inferences are not firmly established. A new approach to calibrating these 2 parameters is suggested from analyses of a section of upper Tertiary dolomites from the Bahamas.

In an interval of dolomite, 120 m (394 ft) thick from a core taken on San Salvador Island, mole % MgCO₃ is correlated positively with δ¹⁸O, and negatively with strontium. Strontium substitutes mainly for calcium, thus the negative correlation with the mole % MgCO₃. Dolomites are enriched between 3 to 7% in δ¹⁸O as compared with coprecipitated calcite, and thus the positive correlation. These two covariations indicate the need to consider the stoichiometric coefficient of dolomites, and to normalize strontium concentrations and δ¹⁸O with their respective stoichiometric coefficients before inferring their relationship with fluid composition.