In order to apply Sr/Ca and 44Ca/ 40Ca fractionation during calcium carbonate (CaCO 3) formation as a proxy to reconstruct paleo-environments, it is essential to evaluate the impact of various environmental factors. In this study, a CO 2 diffusion technique was used to crystallize inorganic calcite from aqueous solutions at different ionic strength/salinity by the addition of NaCl at 25°C. Results show that the discrimination of Sr 2+ versus Ca 2+ during calcite formation is mainly controlled by precipitation rate (R in μmol/m 2/h) and is weakly influenced by ionic strength/salinity. In analogy to Sr incorporation, 44Ca/ 40Ca fractionation during precipitation of calcite is weakly influenced by ionic strength/salinity too. At 25°C the calcium isotope fractionation between calcite and aqueous calcium ions (Δ 44/40Ca calcite-aq=δ 44/40Ca calcite-δ 44/40Ca aq) correlates inversely to logR values for all experiments. In addition, an inverse relationship between Δ 44/40Ca calcite-aq and logD Sr, which is independent of temperature, precipitation rate, and aqueous (Sr/Ca) aq ratio, is not affected by ionic strength/salinity either. Considering the logD Sr and Δ 44/40Ca calcite-aq relationship, Sr/Ca and δ 44/40Ca calcite values of precipitated calcite can be used as an excellent multi-proxy approach to reconstruct environmental conditions (e.g., temperature, precipitation rate) of calcite growth and diagenetic alteration.
ASJC Scopus subject areas
- Geochemistry and Petrology