Buried organic material is degraded by microbes, thermogenically altered by heat and pressure, or buried more deeply and lost to the surface carbon cycle. Methane produced during microbial (also called “biogenic”) and thermogenic decomposition can slowly migrate through overlying sediment with fluids or rise rapidly along faults or other permeable paths. As methane-saturated fluids rise and cool, excess methane forms gas bubbles below the base of gas hydrate stability, BGHS. Above the BGHS, excess methane generally forms methane hydrate, but can also form bubbles (Suess et al., 1999, Liu and Flemings 2006).
From collection: Frozen Heat - A Global Outlook on Methane Gas Hydrates