A calibration equation between Δ 48 values of carbonate and temperature

Rationale Information on the temperature of formation or alteration of carbonate minerals can be obtained by measuring the abundance of the isotopologues 47 and 48 (Δ 47 and Δ 48 values) of CO 2 released during acid dissolution. The combination of these two proxies can potentially provide a greater insight into the temperature of formation, particularly if the carbonate minerals form by non‐equilibrium processes. Methods We have precipitated calcium carbonates at seven temperatures between 5 and 65°C and measured their δ 48 values using a Thermo‐253 plus isotope ratio mass spectrometer. The values were transformed to Δ 48 values in the conventional manner and then converted to the carbon dioxide equilibrium scale. Results Using the Δ 48 values, we have established an empirical calibration between temperature and Δ 48 values: Δ 48 = 0.0142 ± 0.0012 × 10 6 / T 2 + 0.088± 0.014R 2 = 0.96 .Conclusions The calibration line produced allows the determination of the temperature of natural carbonates using the Δ 48 values and agrees with the measurements of the Δ 47 and Δ 48 values of some carbonates assumed to have formed under equilibrium conditions.