124 / 2025-04-02 10:38:27

Reexamination and reidentification of ocean oxygenation event in the wake of the Marinoan glaciation

Earliest Ediacaran,Ocean oxygenation,Redox-sensitive elements,Redox-stratified ocean

Theme 4: Microbial and Biogeochemical Evolution through Time > Session 4b: Roles of Microbes in Shaping Our Habitable Earth

The earliest Ediacaran oceanic oxygenation event in the wake of the Marinoan glaciation defined as OOE-A (~635–632 Ma) represents a crucial component of the Neoproterozoic Oxygenation Event. This event was primarily identified based on high enrichments of redox-sensitive elements (RSEs) in the basal Ediacaran Doushantuo Formation of South China. However, its robustness on a global scale has been subject to debate. Here, we reexamine the proposed OOE-A through an integrative study of correlative successions across the shelf-to-basin transect in South China, along with records from other continents. Sedimentary and geochemical evidence, including iron speciation, RSE concentrations, organic carbon isotopes, and pyrite sulfur isotopes, collectively suggest an oxic shelf and an anoxic (intermittently euxinic) basin, with a fluctuating chemocline around the upper slope setting in South China. Importantly, a diffusion-reaction model integrating sedimentation rates and authigenic RSE concentrations suggests that the discrepancies in RSE enrichment levels between the basal Ediacaran black shales of South China and northwestern Canada can be reconciled if seawater Mo and U concentrations were only 0.5–3% and 1.5–6% of their modern values, respectively. This finding contradicts the traditional viewpoint of the expansion of seawater RSE reservoirs in response to a widely oxygenated ocean, while highlighting a significant role of slow sedimentation rates in driving authigenic RSE enrichments in anoxic marine facies locally. From both spatial and temporal perspectives, this study refines the magnitude of OOE-A in South China, characterizing it as a transient oxygenated shelf environment in a redox-stratified ocean. The reexamination of OOE-A provides new insights into other documented oceanic oxygenation events and the intricate relationship between marine oxygenation and biological evolution during the Neoproterozoic Oxygenation Event.