Abstract
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.