Mud volcano gas hydrates in the Gulf of Cadiz

This paper presents new geochemical data on gas-hydrate-bearing mud volcanoes discovered for the first time in the Gulf of Cadiz during cruises TTR9 and TTR10 of the R/V Professor Logachev in 1999-2000. The estimated gas hydrate content is 3-16% of sediment volume and 5-31% of pore space volume. Estimated values of the water isotopic composition for the Ginsburg mud volcano are very heavy for delta(18)O (up to +53parts per thousand.) and light for deltaD (up to - 210parts per thousand). Gas released from the hydrates contains 81% of C-1 and 19% of C2+. The inferred source of the gas in the hydrates is enriched in C-2-C-6 (less than or equal to 5%), indicating that the gas has a thermogenic origin. Gas hydrate of cubic structure II should be formed from a gas of such composition. It is interpreted that the composition of the mud volcano fluid corresponds to deep oil basins below the Gulf of Cadiz.