Sulfate triple-oxygen-isotope evidence confirming oceanic oxygenation 570 million years ago

The largest negative inorganic carbon isotope excursion in Earth’s history, namely the Ediacaran Shuram Excursion (SE), closely followed by early animal radiation, has been widely interpreted as a consequence of oceanic oxidation. However, the primary nature of the signature, source of oxidants, and tempo of the event remain contested. Here, we show that carbonate-associated sulfate (CAS) from three different paleocontinents all have conspicuous negative (17)O anomalies (Δ′(17)O(CAS) values down to −0.53‰) during the SE. Furthermore, the Δ′(17)O(CAS) varies in correlation with its corresponding δ(34)S(CAS) and δ(18)O(CAS) as well as the carbonate δ(13)C(carb), decreasing initially followed by a recovery over the ~7-Myr SE duration. In a box-model examination, we argue for a period of sustained water-column ventilation and consequently enhanced sulfur oxidation in the SE ocean. Our findings reveal a direct involvement of mass-anomalously (17)O-depleted atmospheric O(2) in marine sulfate formation and thus a primary global oceanic oxygenation event during the SE.