A New Oil and Gas Seep in Lake Baikal

A new oil show, Zelenseep, was discovered on the eastern shore of Middle Baikal. It is characterized by natural gas discharge (seep) from the lake floor and by accumulation of oil (high- molecular-weight bitumen fraction) and gas hydrates in the top layer of the sediments. The gas in the sediments and gas hydrates is composed of 99% thermogenic methane. The carbon isotope composition (δ 13 (С–С 1 )) ranges from –48.1 to –48.8‰ for methane in the sediment and from –49.4 to –50.2‰ for that in the hydrates. Oil is not discharged into the water column. N-alkanes and isoprenoids are not found in the oil; polycyclic aromatic hydrocarbons are detected at the 1800– 2200 ppm level, including 50–90 ppm of rethene and 120–140 ppm of perylene. The perylene concentration evidences major transformation undergone by the oil on its migration path from the source. The presence of rethene in the oil is indicative of its continental origin, and that of biomarkers, hopanes, of its identity with the Baikal naphthenic-aromatic oils. The sediments of earlier Cenozoic age in Baikal Basin, occurring in its central deep-water part, were assigned to organic matter source.