PLIOCENE-QUATERNARY METHANE EMISSION FROM SOUTH CASPIAN MUD VOLCANOES

South Caspian sedimentary basin is a unique area with thick Mesozoic-Cenozoic sediments (up to 30-32 km) characterized by an extremely high fluidgeneration potential. A great amount of active mud volcanoes and volume of their gas emissions prove the vast scale of fluidgeneration. From 187 onshore and 170 offshore mud volcanoes estimations annually erupt more than 109 cubic meters of gases consisting of CH4 (79-98%), and small admixture of C2H6, C3H8, C4H10, C5H12, CO2, N, H2S, Ar, He. The large accumulations of gas hydrates confined to bottom sediments of the Caspian Sea mud volcanoes craters fields (interval 0-0.4m, sea depth 480m) and to volcanoes body at the depth 480-800 from the sea bottom. Here gas hydrates consist of CH4 (58.7-87%), C2H6 (10.4-19.4%), C3H8 (1.8-15.8%), iC4H10 (0.1-2.5%), C4H10 (0.4-2.0%), C5H12 (0.00-0.68%). Resources of HC gases in hydrates saturated sediments up to depth 100 m are estimated in 0.2x1015m3-8x1015 cubic meters. According to the average rate of sedimentation in these parts of the Caspian Sea (2mm/year) the age of submarine (prebottom) gas hydrates is not older than 200 years. Amount of HC gases concentrated in them is 1011-1012 cubic meters. Caspian Sea, being inland closed basin is very sensitive to climatic and tectonic events expressed in sea level fluctuations. In regressive stages as a result of sea level fall and reducing of hydrostatic pressure the decomposition of gas hydrates and releasing of great volume of HC gases consist mainly of methane are observed. From the data of deep drilling, seismoacoustics, deep seismic mud volcanic activity in South Caspian basin started since Lower Miocene. The most intensity it reached at the border of Miocene and Pliocene and was associated with dramatic Caspian Sea level fall in Lower Pliocene up to 600 m, which led to isolation of PaleoCaspian from Eastern ParaTethis. Catastrophic reducing of PaleoCaspian size with increasing scale of mud volcanic activity caused the oversaturation and intoxication of water by methane led to mass extinction mollusks, fishes and other group of sea inhabitants. In Upper Pliocene and Quaternary mud volcanism occurred under the conditions of semi-closed sea periodically connected with Pontian and Mediterranean basins. Those stages of Caspian Sea history are characterized by the revival of Caspian organic world.