Gas hydrate dissociation in the Lorca Basin (SE Spain) during the Mediterranean Messinian salinity crisis

Abstract

The Tortonian marls which were deposited in the Lorca Basin (SE Spain) prior to the Messinian Tripoli Formation contain discontinuous levels of indurated nodules and massive layers, up to a few meters thick, of diagenetic dolomite. The oxygen and carbon isotopic compositions of these dolomites indicate that the carbonate diagenesis occurred mostly in 13 C-rich and 18 O-rich to 18 O-poor solutions. The vertical distribution of the δ values of these dolomites is interpreted as the result of the past occurrence of gas hydrate reservoirs where the methane source probably originated from the organic-rich marls. We postulate that the gas hydrates contained in the Tortonian marls were destabilized during the water level drops related to the Messinian salinity crisis. Associated sedimentary structures include numerous syn-sedimentary deformations and brecciation which are the expression of important sedimentary instabilities, which could have been generated during the gas hydrates decomposition.