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 ¹⁷O anomalies (Δ'¹⁷O_CAS values down to -0.53‰) during the SE. Furthermore, the Δ'¹⁷O_CAS varies in correlation with its corresponding δ³⁴S_CAS and δ¹⁸O_CAS as well as the carbonate δ¹³C_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 ¹⁷O-depleted atmospheric O₂ in marine sulfate formation and thus a primary global oceanic oxygenation event during the SE.