Methanogenesis and siderite precipitation in coal: Significance for carbon sequestration

Abstract

Coal deposits derived from peat play a key role in Earth’s carbon cycle by facilitating the burial and transformation of organic carbon. However, the role of mineral precipitation in peat-forming environments, particularly the microbially mediated formation of siderite and its contribution to carbon cycling, remains poorly understood. Here, we investigate a Jurassic siderite-bearing coal seam to reconstruct mineral paragenesis and constrain diagenetic conditions during peat accumulation. Authigenic, 13C-rich siderite associated with methanogenesis formed under acidic and reducing conditions, consistent with precipitation equilibrium simulations that show enhanced siderite saturation at elevated CO2 pressures. Our results suggest that siderite genetically associated with coal may have acted as an inorganic carbon sink by limiting greenhouse-gas release during peat decomposition, thereby reducing CO2 emission by 2% within the studied paleo-peat deposit and sequestering ∼12.67 Gt of CO2 across three Jurassic coal basins. These findings reveal a previously overlooked pathway for carbon fixation in coal measures, with potential for both deep-time climate and modern greenhouse gas mitigation.