New distribution coefficient for the incorporation of strontium into dolomite and its implications for the formation of ancient dolomites

Late Tertiary dolomites from the Bahamas exhibit a strong inverse correlation between Sr and mol% MgCO ₃ . It is proposed that this relation is a result of a distribution coefficient dependent on the concentration of Ca in dolomite. Because these dolomites precipitated from water with a Sr ²⁺ /Ca ²⁺ ratio similar to that of seawater, distribution coefficient (D _Sr ^dolomite ) of 0.0118 is calculated for Sr in stoichiometric dolomite. This coefficient increases by about 0.0039 for every additional mol% CaCO ³ in monstoichiometric dolomite. These data have three important implications. First, the new D _Sr ^dolomite ) is substantially lower than previously suggested. Second, a relation has been established among the Sr ²⁺ /Ca ²⁺ ratio of dolomite-forming waters, the major element composition of dolomites, and the Sr content of dolomites, allowing the determination of the Sr ²⁺ /Ca ²⁺ ratio of fluids involved in the formation of ancient dolomites. Third, some published data sets on dolomites show a similar relation between Sr content and major element composition suggesting that these dolomites may also have formed from seawater. Other data sets deviate from the correlation defined by Little Bahama Bank dolomites, indicating either dolomitization in fluids other than seawater or changes of the Sr ²⁺ /Ca ²⁺ ratio of seawater through time.