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Most previous studies focused on the redox state of the deep water, leading to an incomplete understanding of the spatiotemporal evolution of the redox‐stratified ocean during the Ediacaran–Cambrian transition. In order to decode the redox condition of shallow marine environments during the late Ediacaran, this study presents I/(Ca + Mg), carbon and oxygen isotope, major, trace, and rare earth element data of subtidal to peritidal dolomite from the Dengying Formation at Yangba, South China. In combination with the reported radiometric and biostratigraphic data, the Dengying Formation and coeval successions worldwide are subdivided into a positive δ13C excursion (up to ~6‰) in the lower part (~551–547 Ma) and a stable δ13C plateau (generally between 0‰ and 3‰) in the middle‐upper part (~547–541 Ma). The overall low I/(Ca + Mg) ratios (<0.5 μmol/mol) and slightly negative to no Ce anomalies (0.80 < [Ce/Ce*]SN < 1.25), point to low‐oxygen levels in shallow marine environments at Yangba. Moreover, four pulsed negative excursions in (Ce/Ce*)SN (between 0.62 and 0.8) and the associated two positive excursions in I/(Ca + Mg) ratios (up to 2.02 μmol/mol) are observed, indicative of weak oxygenations in the shallow marine environments. The comparison with other upper Ediacaran shallow water successions worldwide reveals that the (Ce/Ce*)SN and I/(Ca + Mg) values generally fall in the Precambrian range but their temporal trends differ among these successions (e.g., Ce anomaly profiles significantly different between Yangba and the Yangtze Gorge sections), which point to low oxygen levels with high redox heterogeneity in the surface ocean. This is consistent with the widespread anoxia as revealed by low δ238U values reported by previous studies. Thus, the atmospheric oxygen concentrations during the late Ediacaran are estimated to be very low, similar to the case during the most Mesoproterozoic to early Neoproterozoic period. [ABSTRACT FROM AUTHOR]

The Permian–Triassic mass extinction (PTME), the most devastating extinction event in Phanerozoic history, has witnessed the demise of almost 80% of marine gastropod genera. Despite the vast scale of the extinction event, the recovery of some groups of marine gastropods has been curiously fast, contrasting with the delayed recovery of many other marine clades. Understanding the rapid recovery of gastropods after the PTME represents a major palaeobiological conundrum, since oxygen‐dependent taxa are expected to have been severely impacted by anoxic oceanic conditions of the PTME. The controversial microbialite refuge hypothesis has been proposed as a potential explanation of this pattern, arguing that marine invertebrates were associated with oxygen‐producing microbial mats during the PTME, which provided a suitable microhabitat for survival within hostile anoxic conditions. To better understand the dynamics of gastropod recovery after the PTME, we studied a gastropod fauna collected from the basal Daye Formation (earliest Triassic) at the Yangou section in Leping County, Jiangxi Province, south China, allowing us to capture a snapshot of the marine fauna immediately after the PTME. Altogether, 13 microgastropod species belonging to 12 genera were recorded, representing the most diverse Induan (earliest Triassic) gastropod fauna in the world known to date. The fact that the Yangou assemblage, along with the second most diverse Griesbachian gastropod fauna from the Wadi Wasit section in Oman, is not associated with microbial buildups implies that microbial mats probably did not play a key role as refuges for marine invertebrates during the PTME. On the other hand, the Yangou fauna suggests that non‐anoxic shallow lagoon systems were more likely to have acted as refuges for marine invertebrates during the PTME. [ABSTRACT FROM AUTHOR]