Natural gases emanating from the bottom of Baikal occur ubiquitously along the shoreline, but their open sources are the most crowded at the Selenga subaqueous delta plain. In spring, gas seeps are visible as steamthroughs in the lake ice. We studied fifty-four of these steamthroughs. The gases escaping are mostly methanous (up to 75 vol.% methane), but highly nitrogenous (up to 80 vol.% nitrogen) seeps also occur.
In addition to open gas sources associated with steamthroughs, cryptic discharge of the gases proceeds over the whole area of the Ust’-Selenga Depression (USD). Chemical types of these gases show areal zoning, from nitrogenous in the piedmont periphery of the depression to methanous in the lower delta plain.
A combined analysis of geological, geophysical, and geochemical data strongly suggests that the USD sediment cover is a powerful source of hydrocarbon gases. The similarity of its geological structure to that of the South Caspian Depression allows us to predict the existence of mud volcanoes in Baikal.
Cenozoic depressions of Baikal together with its sedimentary bed make up a potentially gas-bearing basin. The Baikal bottom is a zone of predominant hydrocarbon production, whereas the Selenga delta and other depressions are zones of their transit and accumulation. A regional cap of the natural reservoirs beneath the Baikal bottom may be a gas hydrate layer. Prognosis for oil deposits is poor, because the studied gases are extremely dry, and the bitumen contents in USD sediments and grounds are very low. The presented data and discussion open new ways to consider the Baikal geology.