Abstract
Sulfate-driven anaerobic oxidation of methane (SD-AOM) is ubiquitous in marine sedimentary environments, governing the global methane budget and the redox evolution of Earth's surface. Tracing SD-AOM and organoclastic sulfate reduction (OSR) from the pyrite archive is key to the reconstruction of SD-AOM activity and paleoenvironmental interpretation. However, discriminating the origins of pyrite – basically SD-AOM and OSR – is commonly challenging due to frequent overlap of δ34Spy values. Multiple sulfur isotopes of pyrite are expected to be an effective tool to distinguish between OSR and SD-AOM, yet variable uncertainties and unknowns remain. Here we investigated the δ34S and Δ33S values of pore-water sulfate and authigenic pyrite from a piston core taken on the continental slope of the South China Sea. A positive Δ33S - δ34S correlation of pore-water sulfate is observed in the upper OSR-dominated zone, resulting in Δ33S and δ34S values of sulfate diffusing into the sulfate-methane transition zone (SMTZ) >0.1‰ and >30‰ larger than the corresponding values of seawater sulfate. A negative Δ33S - δ34S trajectory of pore-water sulfate and pyrite is observed for the SMTZ, agreeing with low sulfur isotope fractionation characteristic for SD-AOM and a diagnostic large Δ33S - δ34S field of SD-AOM-derived pyrite. These findings elucidate that the multiple sulfur isotope systematics of pyrite in methane-bearing sediment depends on (1) mass transport effects of dissolved sulfate and sulfide, (2) the relative contribution of OSR and SD-AOM to the pore-water sulfide and pyrite pools, and (3) the sulfur isotope fractionation during microbial sulfate reduction. Our study highlights the importance of mass transport dynamics on the isotopic composition of pyrite, a factor that needs to be considered in any attempt to reconstruct the origin of early diagenetic pyrite and the paleoenvironmental setting with multiple sulfur isotopes.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
