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 dredg ed from the borehole which was drilled under a 354 m thick water layer of L ake Baikal. The structural and geochemical specialization of clay minerals in bottom se diments of Lake Baikal has been established for the first time to a depth o f more than 100 m. The quantitative composition of mineral phases of a thin -pelitic fraction is calculated with the help of computing procedures "Simp lex". It is shown that smectites are represented by beidellite, montmorillo nite, and, to a smaller degree, nontronite. They actually reflect the range of mineral varieties of this group, which is characteristic for allochthon ous and autochthonous genesis. Terrigene smectites in sediments are indicat ive of semi-arid and semi-humid climate in the Miocene and, to a smaller de gree, in the Pliocene. The acme of diatoms and maximum abundances of smecti tes may be linked with the thawing of glaciers and ices whose regelation wa ters are able to transport terrigene smectite and carry a great amount of d issolved silica necessary for building a silica framework of this variety o f phytoplankton. Also, the reserve of smectites considerably grew during au thigenic mineralization. The proof is examination of samples on SEM.