A calibration equation between Δ₄₈ values of carbonate and temperature

Information on the temperature of formation or alteration of carbonate minerals can be obtained by measuring the abundance of the isotopologues 47 and 48 (Δ₄₇ and Δ₄₈ values) of CO₂ 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.

We have precipitated calcium carbonates at seven temperatures between 5 and 65°C and measured their δ⁴⁸ values using a Thermo-253 plus isotope ratio mass spectrometer. The values were transformed to Δ₄₈ values in the conventional manner and then converted to the carbon dioxide equilibrium scale.

Using the Δ₄₈ values, we have established an empirical calibration between temperature and Δ₄₈ values: [Formula: see text] CONCLUSIONS: The calibration line produced allows the determination of the temperature of natural carbonates using the Δ₄₈ values and agrees with the measurements of the Δ₄₇ and Δ₄₈ values of some carbonates assumed to have formed under equilibrium conditions.