Fig. 1: Calculated U–Pb dates and initial ²⁰⁷Pb/²⁰⁶Pb ratios.

a Comparison between calculated U–Pb dates and stratigraphic ages of the carbonate strata. Most calculated values plot below the 1:1 ratio line indicating that they are significantly younger compared to stratigraphic ages. Otherwise, semi-transparent points mark samples with U–Pb dates significantly older than their stratigraphic ages, possibly due to contribution of Pb from a detrital source. Large uncertainties in U-Pb dates, presented as 2 Standard Deviation (SD) error bars, are common to carbonate samples that typically suffer from low ranges of ²³⁸U/²⁰⁶Pb. b Calculated initial ²⁰⁷Pb/²⁰⁶Pb ratios over time. Most values plot below the predicted line of isotopic evolution of terrestrial Pb³⁵, consistent with Pb-isotope re-homogenization 10–100’s of millions of years after deposition. Four samples plot above the trend, of which two have U–Pb dates older than their stratigraphic ages (semi-transparent). Gray rectangle is an uncertainty envelope for marine ²⁰⁷Pb/²⁰⁶Pb values, considering the observed range of values among pre-industrial water sources^{38,40,41,42,45}. Error bars are 2 SD. Source data are provided as a Source Data file.