582 ISSN 0145-8752, Moscow University Geology Bulletin, 2018, Vol. 73, No. 6, pp. 582–587. © Allerton Press, Inc., 2018. Original Russian Text © G.G. Akhmanov, O.M. Khlystov, M.A. Solovyeva, V.N. Efremov, O.N. Vidishcheva, A. Mazzini, A.A. Kudaev, I.A. Bulanova, A.A. Barymova, E.K. Gordeev, M.T. Delengov, E.D. Egoshina, Ya.V. Sorokoumova, P.O. Ponimaskin, 2018, published in Vestnik Moskovskogo Universiteta, Seriya 4: Geologiya, 2018, No. 5, pp. 111–116. Newly Discovered Hydrate-Bearing Structure in Lake Baikal 1,2 G. G. Akhmanov a, *, O. M. Khlystov b , M. A. Solovyeva c , V. N. Efremov c , O. N. Vidishcheva a , A. Mazzini d , A. A. Kudaev a , I. A. Bulanova a , A. A. Barymova e , E. K. Gordeev a , M. T. Delengov a , E. D. Egoshina a , Ya. V. Sorokoumova a , and P. O. Ponimaskin f a Department of Geology, Lomonosov Moscow State University, Moscow, 119991 Russia b Limnological Institute, Russian Academy of Sciences, Irkutsk, 664033 Russia c OOO “Seismic Data Analisys Center of Moscow State University”, Moscow, 119992 Russia d Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Oslo, @ Norway e OOO “Marine Research Center of Moscow State University”, Moscow, 119992 Russia f LLC “SPLIT”, Moscow, 121205 Russia *e-mail: akhmanov@geol.msu.ru Received July 30, 2018 Abstract—A new deep-water hydrate-bearing structure, named after Moscow State University (MSU), has been discovered on July 29, 2018 during the geological-geophysical research of the Class@Baikal project. The structure lies on a fault scarp at the bottom of the central basin of Lake Baikal at a water depth of 1380 m (coordinates N 52°52′/E 107°07′). The “MSU” structure is sub-isometric in planar view, 500 m in diameter, and reveals a multi-summit morphology. Results of initial investigations show an active fluid seepage and gas- hydrate formation within the discovered structure. Laboratory analyses of the sampled gases indicate a sig- nificant concentration of thermogenic hydrocarbons. Keywords: gas hydrates, hydrocarbon gases, seafloor seepages, bottom sampling, seismic profiling, Lake Baikal DOI: 10.3103/S0145875218060029 INTRODUCTION On July 29, 2018 during a joint geological and geo- physical expedition of the Department of Geology (Lomonosov Moscow State University) and the Lim- nological Institute of Siberian Branch of Russian Academy of Sciences onboard the R.V G.Yu. Veres- chagin a hydrate-bearing structure was discovered in the central basin of Lake Baikal. The discovery was conducted in the framework of the Class@Baikal (Floating University) project. During the expedition the morphology and the inner structure of this positive feature were studied, bottom sediment samples were collected, and sediment pore gas was sampled from the cores. The structure was named “MSU” (after the Moscow State University). Baikal is the largest and oldest fresh-water basin on the planet and the only lake where natural accumula- tions of gas hydrates have been discovered. Gas hydrates (clathrates) are ice-like crystals consisting of hydrocarbon gases trapped inside cages of frozen water molecules. They are stable at low temperatures and high pressure conditions when constant gas influx occurs. Theoretical studies and indirect evidence suggest- ing the presence of hydrates in the deep Baikal basins have been the topic of discussions since the 80’s (Gol- mshtok et al., 1997; Golubev, 1997; Hutchinson et al., 1991; Efremova et al., 1980). The first evidence of the presence of gas hydrates in Baikal sediments was pro- vided in 1997 during the BDP-97 project when clath- rates of biogenic methane were collected at a depth at 121 and 161 mblf (Kuz’min et al., 1998). Then, shallow gas hydrate accumulations, observed as lenses and lay- ers, were discovered in 2000 at the “Malenkiy” struc- ture in the southern basin of the lake (Klerkx et al., 2003). Between 2000 and 2017 national and interna- tional projects discovered several hydrate-bearing structures in the southern and central basins of Lake Baikal at depths between 400 and 1500 m in slope and abyssal plane settings (Khlystov et al., 2013, 2017). To date, most of the known structures are located at a shallow depth. MSU is the fifth structure discovered at depth >1300 m. The goal of this article is to provide (1) the first description of the “MSU” morphology and 1 The article was translated by the authors. 2 The Class@Baikal-2018 cruise was funded by E.A. Bakay, by the Department of Geology of Lomonosov Moscow State Univer- sity, by OOO “Seismic Data Analisys Center of Moscow State University”, OOO “Marine Research Center of Moscow State University”, through the project no. 0345-2016-0007 of LIN SB RAS and the grant of the Russian Foundation for Basic Research (project no. 18-35-00363).