The study of clay for a long time lagged behind the needs of practice, which was due to their high dispersion, requiring the use of high-resolution research equipment to view them at high magnifications. Only with the advent of scanning electron microscopy (SEM), it became possible to study the microstructural features of clay minerals. In this paper, clay minerals were studied from sediments exposed by wells 513 and 508 in the Uro region (Chitkan Depression), in the south of Barguzin Valley. Microstructural characteristics of clay minerals were studied in a stratigraphic sequence of the lacustrine (Tankhoi Formation) and alluvial, ocher (Anosovskaya Formation) units. The clay fraction was extracted by an elutriation method. The processing of the material was carried out in the joint laboratory of modern research methods in dynamic and engineering geology of the ISU and IEC SB RAS. Studies of clay minerals were performed on a scanning electron microscope (SEM) with an EMF spectrometer at the Limnological Institute SB RAS. In the samples, kaolinite, montmorillonite, chlorite, and three types of hydromica are identified. According to the results of the research, the boundary between the Tankhoi and Anosovska Formations in Barguzin Valley was defined. The data obtained on clay mineral compositions were correlated with those of bottom sediments detected in the well BDP-98 on the Academic Ridge of Lake Baikal.

Alokla Riyad, Postgraduate, Junior Research Scientist, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, tel.: 8(3952)24-32-80, University of Aleppo, University district, Aleppo, Syria, tel.: +(963) 21 267300, e-mail: riyad.198762@gmail.com 

Chuvashova Irina Sergeevna, Candidate of Sciences (Geology and Mineralogy), Associate Professor, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, tel.: 8(3952)24-32-80, Senior Researcher, Institute of the Earth's Crust, SB RAS, 128, Lermontov st., Irkutsk, 664033, Russian Federation, tel.: 8(3952)51-16-59, e-mail: chuvashova190684@mail.ru 

Rasskazov Sergey Vasilevich, Doctor of Sciences (Geology and Mineralogy), Professor, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, tel.: 8(3952)24-32-80, Head, Laboratory of Isotopiec and Geochronological Studies, Institute of the Earth's Crust SB RAS, 128, Lermontov st., Irkutsk, 664033, Russian Federation, tel.: 8(3952)51-16-59, e-mail: rassk@crust.irk.ru 

Danilova Marina Valerievna, Engineer, Institute of the Earth's Crust SB RAS, 128, Lermontov st., Irkutsk, 664033, Russian Federation, tel.: 8(3952)51-16-59, e-mail: maridan@gmail.com

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