Dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event

Abstract

Compared with Phanerozoic strata, sulfate minerals are relatively rare in the Precambrian record; this is probably due to the lower concentrations of sulfate in dominantly anoxic oceans. Here, we present a compilation of sulfate minerals that are stratigraphically associated with the Ediacaran Shuram excursion (SE) – the largest negative δ13C excursion in Earth history. We evaluated 15 SE sections, all of which reveal the presence of sulfate minerals and/or enriched carbonate-associated sulfate concentrations, suggesting a rise in the sulfate reservoir. Notably, where data are available, the SE also reveals considerable enrichments in [Ba] relative to pre- and post-SE intervals. We propose that elevated seawater sulfate concentrations during the SE may have facilitated authigenesis of sulfate minerals. At the same time, the rise in Ba concentrations in shelf environments further facilitated barite deposition. A larger sulfate reservoir would stimulate microbial sulfate reduction and anaerobic oxidation of organic matter (including methane), contributing to the genesis of the SE. The existence of sulfate minerals throughout the SE suggests that oxidant pools were not depleted at that time, which challenges previous modelling results. Our study highlights the dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event.Supplementary material: SEM and EDS data and figures S1-S4 and tables S1-S3 are available at: https://doi.org/10.6084/m9.figshare.c.5602560Thematic collection: This article is part of the ‘Sulfur in the Earth system’ collection available at: https://www.lyellcollection.org/cc/sulfur-in-the-earth-system