Constraints and interpretation of ⁸⁷Sr/⁸⁶Sr ratios in Cenozoic dolomites

Replacement dolomitization by seawater has been modeled in order to quantify the Sr‐isotope signature in Cenozoic dolomites as a function of precursor mineralogy and ⁸⁷Sr/⁸⁶Sr ratio, reaction stoichiometry and ⁸⁷Sr/⁸⁶Sr ratio of the dolomitizing fluids. High Sr carbonates, such as aragonite, may introduce a significant precursor memory into an otherwise seawater dominated Sr‐isotope signature if small quantities of seawater per unit volume of precursor carbonate are involved. Dolomitization of low Sr carbonates (i.e. low‐Mg calcite) are shown to create an isotopic signature indistinguishable from that of the seawater involved in the reaction. Therefore, by comparison with the Sr‐isotope evolution curve of seawater, the‐ ⁸⁷Sr/⁸⁶Sr ratios of the dolomites can be used to record the oldest possible age of dolomitization and the youngest age of deposition. The implications for this approach have been applied to data obtained from a dolomitized core from Little Bahama Bank, Bahamas. Two periods of dolomitization are recognized, one in the early Late Miocene involving Middle Miocene or older rocks, and a second one around 2.4 Ma ago affecting early Pliocene carbonates.