Fig. 2.

Strontium isotopic composition and barium baseline values of the fossil bivalve shells. (A) mean values (black symbols) and single measurements (coloured points) of ⁸⁷Sr/⁸⁶Sr from bivalve shells; the Eocene global seawater ⁸⁷Sr/⁸⁶Sr reconstruction is from McArthur et al.²³ (black curve, grey shading—uncertainties of the LOWESS fit) with modern oceanic water ⁸⁷Sr/⁸⁶Sr variability (± 21 × 10⁻⁶, dashed lines)⁶; average standard error for single measurements is displayed by the black vertical bar (2 SE = 18 × 10⁻⁶); (B) mean values (black symbols) and single measurement (coloured points) of ⁸⁷Sr/⁸⁶Sr from bivalve shells normalised to the relevant Eocene seawater ⁸⁷Sr/⁸⁶Sr value²³; the seawater ⁸⁷Sr/⁸⁶Sr value for normalisation is that for the mean age of each sampling site (Supplementary Material 2); average standard error for single measurements is displayed a black vertical bar (2 SE = 18 × 10⁻⁶); (C) bivalve shell Ba/Ca baseline (± 2SD); coloured symbols indicate mean age and horizontal bars, while the shaded areas show the age uncertainty for each sampling location, in which the plotted samples may fall (Table 1); G Le Guépelle, SW Studley Wood, CV Chaumont-en-Vexin, FR Fleury-La-Rivière, A Aalter, N Nursling; basins are indicated by colour: Paris Basin — red, Hampshire Basin — blue, Belgian Basin — green. Eocene stages are shown in the same colours as the geological time scale²⁴.