Reconstruction of the Ediacaran sulfur cycle and oceanic redox evolution in shallow-water regions of the Yangtze platform, South China

The emergence and proliferation of metazoan lineage in the Ediacaran Period is commonly hypothesized to reflect an increase in the oxygen content of marine environments. However, recent studies suggest that the Ediacaran oceanic redox conditions were spatially heterogeneous and temporally dynamic. In this study, we report high-resolution pyrite S-isotope data (delta S-34(py)) for a continuous Ediacaran drill core that was deposited in a very shallow setting from the Yangtze platform, South China. Combined with petrographic observations, statistics of pyrite framboid diameters, total carbon (TC), total sulfur (TS), trace element, and published data, we attempt to characterize the details of sulfur cycle as well as oceanic redox change in the shallow-water regions of the Yangtze platform during the Ediacaran. The delta S-34(py) profile exhibits a large amplitude of variation, ranging from -13.7 parts per thousand. to 41.4 parts per thousand throughout the drill core. Both global and regional changes in environment could have exerted effects on delta S-34(py) values. For the Doushantuo Formation, distinct delta S-34(py) records from shelf to basin may reflect spatial heterogeneity in sulfate concentrations, depositional environments, and availability of organic matter. Notably, periods of upwelling may cause oxygen-deficient zones within shallow water column and facilitate persistent burial of organic matter and pyrite in shelf regions. Subsequent exposure and weathering of these reduced carbon and sulfur may contribute to the Shuram-Wonoka event. The prevalence of high delta S-34(py) values in the terminal Ediacaran (Dengying Formation) likely indicates an enhanced pyrite burial flux at a global scale, during which extensive marine anoxia might take place. In addition, enrichments of V and U in three shale intervals of the drill core support periods of oxygenation for the Ediacaran oceans.

Automated summary

This study investigates the sulfur cycle and oceanic redox changes during the Ediacaran Period using high-resolution pyrite S-isotope data from a shallow setting in the Yangtze platform, South China. The results suggest that both global and regional environmental changes could affect the delta S-34(py) values, and spatial heterogeneity in sulfate concentrations and depositional environments may be reflected in pyrite records. Additionally, enrichments of V and U support periods of oxygenation in the Ediacaran oceans.