Gas Hydrates Associated With oil and gas Seeps in the Eastern Black Sea: Preliminary Results From TTR Cruise 15 Legs 1 and 2

Seafloor seepage and methane emissions to the water column were studied by several groups and projects during the last five in the western and central part of the Black. Studies on fluid and gas discharge in areas of the eastern Black Sea are very rare. Due to the close relationship to the Greater Caucasus thrust belt and the Eastern Pontides such locations like the Shatsky Ridge, Tuapse Trough and Rioni Basin are of great interest because of their difference in geologic composition in comparison to the western Black Sea. During TTR cruise 15 Legs 1 & 2 we investigated active seep sites in the Russian, Georgian and Turkish Sectors of the Black Sea. During an interdisciplinary approach we used long-range ORKEAN sidescan sonar and deep-towed high-resolution MAK-1M sidescan sonar mapping as well as seismic profiling to locate sites of active fluid and gas discharge. Detailed observations by video-sled and ROV investigations were performed before seafloor sampling by a gravity corer and a TV-grab occurred. Seeps were free gas bubbles are escaping from the sea floor were successfully observed on Kobuleti Ridge (Georgia) at water depths between 1100 - 850 m by acoustic anomalies in the water column on raw sonar data and as high backscatter intensity areas. Since free gas should become converted to gas hydrate in depth below 750 m of the Black Sea, the presence of free gas is explained by fast transport from a large gas reservoir below the lower boundary of the gas hydrate stability field in the sediments. Bottom-seismic reflections are well imaged in the area. The seeps on Kobuleti Ridge (Georgia), as well as on the first anticline of the Tuapse Foldbelt and the Shatsky Ridge are characterised by carbonate and shallow gas hydrate deposits. At four distinct mound locations, three on the Kobuleti Ridge and one on Shatsky Ridge, oil and other higher hydrocarbon gases have been detected for the first time, indicating seepage from deeper petroleum reservoirs.