Authigenic pyrite in marine sediments: Geochemical insights from present and past

Sedimentary pyrite is becoming one of the most promising and reliable archives for biogeochemical processes and environmental evolution of the Earth’s surface today. It represents a major reservoir of sulfur within the global sulfur cycle, with most of its formation taking place in organic-rich sediments along continental margins. Authigenic pyrite typically forms through microbial sulfate reduction coupled to organic matter remineralization or anaerobic oxidation of methane in sediments. Pyrite formation in marine sediments influences global seawater sulfate concentrations and sulfur isotope patterns, reflecting local microbial activities or environmental change, and tracking past seawater chemistry. Applications as a paleoenvironmental proxy rely on characteristic geochemical signatures archived in pyrite, including its sulfur isotopic and trace element compositions. Therefore, a comprehensive understanding of the controls on pyrite geochemistry is critical for the effective application of this proxy in studying the Earth system.

Marine methane-rich sediments alone continental margins, such as seeps, are excellent natural laboratories to study mineral authigenesis, while also being global hotspots of sulfate consumption and authigenic pyrite formation. We present various geochemical datasets including multiple sulfur (³²S, ³³S, ³⁴S, ³⁶S), iron (⁵⁴Fe, ⁵⁶Fe), and molybdenum (⁹⁵Mo, ⁹⁸Mo) isotopic compositions, along with trace element patterns of authigenic pyrite from modern and ancient methane-rich sediments deposited along continental margins. Our results highlight the potential of pyrite geochemistry as a tool to distinguish and characterize different modes and intensities of microbial sulfate reduction during early diagenesis. Furthermore, this study reveals that the trace element inventory of pyrite formed during early diagenesis is affected by sediment composition rather than by seawater. A comprehensive understanding of early diagenetic processes improves our understanding of pyrite formation and its geological implications.