The Black Sea is one of the largest inland seas in the world. Off the shelf, the water depth quickly plunges to an average depth of 2 km. The Black Sea sediments are rich in calcite and organic carbon, the latter showing a high degree of preservation due to anoxia in the waters below 100-150 m. Slope failures and sediment instability related to immense gas and gas hydrate accumulations are serious problems that can lead to the failure of offshore installations. Marine geophysical surveys have been carried out in the Eastern Black Sea basin using state-of the-art technology to produce sonar and high-resolution maps. A number of prominent structures were detected in the area such as slumping, sliding, pockmarks, faults and dome-like structures. In the Turkish near shore and the abyssal plain, shallow gas accumulations have been detected and are continuous about 25-65 m beneath the seafloor. The gas-bearing strata appear as bright spots and cloudy spots, sometimes pockmarks and acoustic blanking. The sediments on the Turkish shelf contain certain concentrations of gas which can seep to the seabed surface and generate pockmarks. Gas-hydrate layers in the sediments often appears as dark and strong reflection pockets on sub-bottom profiler records.
ÇİFÇİ, GÜNAY; DONDURUR, DERMAN; and ERGÜN, MUSTAFA (2002) "Sonar and High Resolution Seismic Studies in the Eastern Black Sea," Turkish Journal of Earth Sciences: Vol. 11: No. 1, Article 5. Available at: https://journals.tubitak.gov.tr/earth/vol11/iss1/5