Fig. 3: Rare-earth element and δ²³⁸U comparison.

A Rare-earth element + yttrium (REY) spider plots for average Olenek Uplift samples (orange; this study), average Nama Group samples that were investigated for U isotopes (blue; ref. 18), and average South China samples that were investigated for U isotopes (green; ref. 17). REY concentrations are normalized to post-Archean Australian shale (PAAS) values. For the Olenek Uplift and Namibian sections, only those samples with Y/Ho ratios >36 were included (no Y/Ho data are available for the South China section). Oxygenated North Pacific seawater at 400 m depth⁴⁴ is plotted for comparison, along with the shallowest depth sample with Y/Ho > 36 from Pleistocene carbonate platform cores in the Bahamas⁴⁹. Highlighted in gray is Ce, showing the presence/absence of a negative Ce anomaly, and Y, showing the positive Y anomaly that indicates a seawater signal. B Cross-plot of Ce/Ce* vs. δ²³⁸U for samples from this study (orange), Namibia (blue; ref. 18), and South China (green; ref. 17). Modern Bahamas median δ²³⁸U value is from ref. 55 and oxic/anoxic Ce/Ce* cutoff value of 0.9 is from ref. 21.