Enigmatic super-heavy pyrite formation: Novel mechanistic insights from the aftermath of the Sturtian Snowball Earth. (1st October 2022)

• Record Type: Journal Article
• Authors: Cai, Chunfang; Lyons, Timothy W.; Sun, Peng; Liu, Dawei; Wang, Daowei; Tino, Christopher J.; Luo, Genming; Peng, Yanyan; Jiang, Lei
• Is Part Of: Geochimica et cosmochimica acta. Volume 334(2022)
• Page Start: 65
• Page End: 82
• Publication Date: 2022-10-01
• Subjects: Superheavy Pyrite -- Organic Sulfur -- Snowball Earth -- Microbial sulfate reduction -- Quadruple Sulfur Isotopes; Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2022.07.026
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: It is not well understood how, in the immediate aftermath of the Sturtian Snowball Earth, marine sulfur cycling resulted in a global distribution of sedimentary pyrite with δ 34 S values higher than coeval seawater. Here, we analyze the quadruple sulfur isotope systematics of organic-bound sulfur (OS) from the lowermost post-Sturtian Datangpo Formation, South China, and identify two generations of OS formation, each sampling an isotopically distinct sulfate reservoir (δ 34 S ≈ 26‰ and 52–93‰) that differentially impacted its respective, co-occurring pyrite. Combining several lines of geochemical evidence, we argue that the first OS generation was the product of a sulfate-impoverished meltwater-influenced setting, with OS preservation being the result of resistance to acid hydrolysis. However, the second OS generation was sourced from H2 S produced in sediments during early diagenesis via microbial reduction of a 34 S-enriched sulfate pool derived from overlying euxinic or ferruginous seawater. This is the first ancient marine data set where all observed pyrite is more enriched in 34 S than its associated OS. Our proposed origin may be applied to global superheavy pyrite (SHP) immediately after the Sturtian and is comparable to processes linked to freshwater-to-marine transitions during rising sea level in the wake of recent glaciation.