Most methane enclosed in gas hydrates is biotic in origin, formed by microbial degradation of sedimentary organic matter. Increasingly, there is evidence that substantial gas hydrate may also be sourced from thermogenic decomposition of organic matter and subsequent migration of this gas into the gas hydrate stability zone. In addition, there is a third potential source of methane that does not involve organic matter at all— abiotic methane, which can be generated by magmatic processes or gaswater- rock reactions in the crust and upper mantle.
Fire in the Ice, The National Energy Technology Laboratory Methane Hydrate Newsletter
U.S. Department of Energy
Johnson, J.E., Waghorn, K.A., Mienert, J., and Bünz, S., 2016. The Potential for Abiotic Methane in Arctic Gas Hydrates. Fire in the Ice, The National Energy Technology Laboratory Methane Hydrate Newsletter, vol. 16, issue 1, p. 9-12. https://www.netl.doe.gov/research/oil-and-gas/methane-hydrates/fire-in-the-ice