A new Chinese national reference material (GBW04481) for calcite oxygen and carbon isotopic microanalysis

Carbonate oxygen (O) and carbon (C) isotopes are widely used as proxies for tracing the processes and physicochemical conditions of many geological events and environmental changes in Earth Science. In particular, O and C isotopic variations at micrometer scales revealed by modern microbeam analytical techniques such as SIMS and NanoSIMS are robust archives for reconstructing palaeoenvironment and paleoclimate changes at annual and seasonal resolution or even higher temporal resolution. Widespread application of carbonate O and C isotopic microanalysis in Earth Sciences, however, has been restricted due to limitation of high-quality carbonate reference materials for O and C isotopic microanalysis. We introduce in this paper a new calcite reference material for calcite O and C isotopic microanalysis. This calcite is collected from a drill-core of the Oka carbonatite complex (Quebec, Canada). We demonstrated that the Oka calcite is fairly homogeneous in O and C isotopic compositions at micrometer scales based on homogeneity test by hundreds of SIMS O and C isotopic analyses. Precise determinations by using conventional gas-source IRMS yield the recommended value of δ¹⁸O_VPDB = ?23.12 ± 0.15‰ (1SD) and δ¹³C_VPDB = ?5.23 ± 0.06‰ (1SD) for the Oka calcite, which has been certified as the first class of Chinese national certified reference material (GBW04481) for O and C isotopic microanalysis.