Evaluating Mg/Ca in belemnite calcite as a palaeo-proxy

The Mg/Ca, Sr/Ca, δ18O and δ13C compositions are given for well-preserved specimens of ten belemnite species/genera from three stratigraphic intervals. The data help assess the use of these proxies for palaeo-oceanography. Samples are from Dorset, UK (Pliensbachian; 5 species); Cambridgeshire, UK (Callovian; 1 species); and the Vocontian Basin, SE France (Valanginian; 4 genera). In none of these belemnite populations (at species or genera level) does Mg/Ca correlate with δ18O. Neither do values of δ18O correlate with Mg/Ca along a microsampled radial profile across a single specimen of Cylindroteuthis puzosiana (Callovian). The use of Mg/Ca is therefore considered to be unreliable as a palaeo-temperature indicator for these belemnite species and genera.