Iron‐Bearing Minerals as Potential Indicators of Paleo‐Methane Seepage Evolution

Abstract Methane (CH 4 ) release and consumption in marine cold seeps are key processes influencing seabed ecology, global climate reconstruction, and hydrate resource exploration. Anaerobic oxidation of methane (AOM), the primary methane consumption mechanism, typically couples with microbial sulfate or metal reduction. Iron‐bearing minerals, including iron sulfides and iron oxides, have recently been recognized as key indicators of methane flux and metabolic pathways in cold seeps. However, their mechanistic roles in reconstructing paleo‐seep evolution under varying methane intensities remain unresolved. Here, we employed an integrated geochemical, mineralogical, and magnetic approach to analyze a seep core recording multistage methane expulsion events, revealing iron‐mineral responses to cold seep evolution. Our results show that iron‐bearing sulfides serve as key tracers of sulfidic environments driven by methane seepage. Their mineralogical attributes depend on both methane flux intensity and ambient iron availability. High methane flux combined with elevated reactive iron levels facilitates the coexistence of metastable iron sulfides (e.g., greigite) with euhedral pyrite. During cold seep evolution, declining methane fluxes and/or sustained sedimentation can trigger a transition from sulfidic to non‐sulfidic conditions in seep‐impacted zones. Microbially produced ferrous iron‐bearing oxides, such as magnetite [formed through Fe(III)‐driven AOM or methanogenesis], may indicate the evolution of cold seeps into anoxic, non‐sulfidic methane environments. These findings demonstrate linkages between iron‐mineral signatures and methane‐cycling processes, highlighting their potential as proxies for reconstructing seep evolution history.