Genetic types of clay minerals in bottom sediments of the Southern Basin of Lake Baikal

The paper treats over the results of lithological studies of the core dredged from the borehole which was drilled under a 354 m thick water layer of Lake Baikal. The structural and geochemical specialization of clay minerals in bottom sediments of Lake Baikal has been established for the first time to a depth of more than 100 m. The quantitative composition of mineral phases of a thin-pelitic fraction is calculated with the help of computing procedures "Simplex". It is shown that smectites are represented by beidellite, montmorillonite, and, to a smaller degree, nontronite. They actually reflect the range of mineral varieties of this group, which is characteristic for allochthonous and autochthonous genesis. Terrigene smectites in sediments are indicative of semi-arid and semi-humid climate in the Miocene and, to a smaller degree, in the Pliocene. The acme of diatoms and maximum abundances of smectites may be linked with the thawing of glaciers and ices whose regelation waters are able to transport terrigene smectite and carry a great amount of dissolved silica necessary for building a silica framework of this variety of phytoplankton. Also, the reserve of smectites considerably grew during authigenic mineralization. The proof is examination of samples on SEM.