Fig. 5: Sr isotope stratigraphy relative ages of oyster shells plotted on the SIS curve (LOWESS version 5)64.

Orange points are from two separate portions of a shell from the Caprock, while maroon point is of a shell from unit Cp in the Roadcut. The average SIS age based on these samples is shown as a blue ellipse. Only inner leaches on the best-preserved specimens are shown. For the full dataset, see Supplementary Note 3 annexed to this paper. Modern seawater 87Sr/86Sr values shown in light blue line. Maximum 2σ external uncertainty for the Sr isotope external standard NBS 987 is shown as red point for comparison (see “Methods” section for details).