Late Paleozoic oxygenation of marine environments supported by dolomite U-Pb dating
Michal Ben‐Israel, Robert Holder, Lyle L. Nelson, Emily F. Smith, Andrew Kylander‐Clark, Uri Ryb
Abstract
Abstract Understanding causal relationships between evolution and ocean oxygenation hinges on reliable reconstructions of marine oxygen levels, typically from redox-sensitive geochemical proxies. Here, we develop a proxy, using dolomite U–Pb geochronology, to reconstruct seawater U/Pb ratios. Dolomite samples consistently give U–Pb dates and initial 207 Pb/ 206 Pb ratios lower than expected from their stratigraphic ages. These observations are explained by resetting of the U–Pb system long after deposition; the magnitude of deviations from expected initial 207 Pb/ 206 Pb are a function of the redox-sensitive U/Pb ratios during deposition. Reconstructed initial U/Pb ratios increased notably in the late-Paleozoic, reflecting an increase in oxygenation of marine environments at that time. This timeline is consistent with documented shifts in some other redox proxies and supports evolution-driven mechanisms for the oxygenation of late-Paleozoic marine environments, as well as suggestions that early animals thrived in oceans that on long time scales were oxygen-limited compared to today.