INTRODUCTION Clumped isotopes (Δ47) in Phanerozoic skeletal carbonates enable direct measurement of palaeotemperatures (TΔ47) and calculation of δ18O in the host fluid (e.g. Price & Passey, 2013; Petersen et al., 2016; Bergmann et al., 2018; Evans et al., 2018; Henkes et al., 2018; Vickers et al., 2020, 2021; de Winter et al., 2021; Barney & Grossman, 2022; Letulle et al., 2022). The analysis of metastable skeletal aragonite is particularly attractive, if the mineral can be proven pristine.