Gas hydrates in Lake Baikal

Subsurface gas hydrates over all the area of their potential occurrence under the floor of Lake Baikal, the only freshwater body where they occur, have been sought and studied since 2000. Two of three known gas hydrates cubic structures (structure 1 biogenic methane hydrates and structure 2 biogenic methane and thermogenic ethane hydrates) have been found in the lake sediments. Large autogenic carbonaceous formations atypical for the lake have been discovered in the areas of gas hydrates occurrence. A new so-called “Baikal” mud volcanoes formation mechanism with shallow roots previously unknown in the seas is described. This mechanism is related to destruction of gas hydrates under their stability zone due to a tectonic activity and warm fluid income. The focus and source of the gas-saturated fluid are determined to be buried depositions of delta fronts, depocenters in the middle of the basins and subsurface ancient sedimentation masses at the eastern flank. The 2018 integrated geological and geophysical survey allowed to discover 54 hydrate-bearing structures represented by 26 mud volcanoes, 18 hydrate mounds, 9 seeps and 1 pockmark. Not only sedimentation masses of various age and many kilometers thick, but also the tectonic dislocation grid determine the distribution of these structures on the floor of Lake Baikal. The fluid pathways are formed through impaired vertical and gently inclined zones of the main rift faults and secondary faults as well as along permeable lithological sedimentation boundaries when the layers rise from the depocenters in the center of the basin to its flanks.