Dynamic redox evolution in the middle-late Mesoproterozoic oceans

The middle Proterozoic (ca. 1.8–0.8 Ga) was thought to be persistently static in eukaryotic biodiversity and oxygenation at the Earth's surface, until the Neoproterozoic Oxygenation Event (NOE). The conventional view of Boring Billion is being challenged by increasing evidence of frequently disturbed oxygenation events in the atmosphere and ocean at ca. 1.6–1.4 Ga, namely the Mesoproterozoic Oxygenation Event (MOE). However, marine redox information during the intermediate period between the MOE and NOE (the middle-late Mesoproterozoic) remains elusive. Here, we report V isotope compositions (δ⁵¹V) of black shales from the middle and upper Shennongjia subgroups in the Shennongjia micro-block, in order to reconstruct the evolution in global marine oxygenation extent during this poorly studied period. The δ⁵¹V values exhibit a large variability, which should have been caused by changes in local depositional environment and global marine oxygenation extent. Based on the sedimentary δ⁵¹V records and local redox information, we reconstruct temporary open-ocean seawater δ⁵¹V variation during the middle-late Mesoproterozoic. The result suggests several episodes of widespread marine oxygenation interspersed with extensive euxinia. It sheds new light into dynamic environmental and eukaryotic evolutions in the middle-late Mesoproterozoic oceans.