Sediments of the Mishikha section were studied on the Tankhoi tectonic step, located between the rise of Khamar-Daban range and subsided bottom of South Baikal Basin. Six packages were distinguished: 1) polyfacial, ocher; 2) “blue clay”, 3) mainly aleuritic with interlayers of brown coal; 4) sand-silt with «blue clay» fragments; 5) sandy and 6) boulder-pebble. In the two lower packages, pollen of broadleaf species is defined, in the third one – pollen of dark coniferous and broadleaf species, in the fourth – pollen of light coniferous pine-larch and dark coniferous forests with well-developed grass-shrub undergrowth, in the fifth and sixth – spores and pollen of vegetation close to modern. From spore-pollen spectra, the 4 lower packets are dated back, respectively, to the upper Eocene, upper Oligocene, lower Miocene, middle-upper Miocene and the 2 upper ones to the Quaternary. The two lower packages referred to the Mishikha stratum, the third one to the Tankhoi Formation, the fourth to the Osinovka Formation, the fifth and sixth to the overlying sedimentary cover. It is proposed that the Eocene-Oligocene Mishikha unit with a significant amount of clay material was formed in a slightly dissected Selenga-Vitim foredeep. The “blue clay” unit marked the erosion of milonites in the Siberian craton suture zone exposed on Proto-Baikal Rise, which separated the Pre-Baikal and Selenga-Vitim foredeeps in the Cretaceous and Paleogene. The lower Miocene Tankhoi Formation continued to denote clay material under conditions of slightly dissected relief. With its contrast increasing in the mid-late Miocene, the clay material of the Tankhoi Formation was changed to alluvial material of the Osinovka Formation, transported from Hamar-Daban Range. The occurrence of clay material in the upper part of the Osinovka formation indicated the erosion of previously accumulated Eocene-Lower Miocene sediments. A new Quaternary reorganization of the relief, associated with the deep Baikal formation resulted in erosion of the Tankhoi tectonic step and accumulation on its surface of sandy and coarse debris.

Al Hamoud Adnan, Postgraduate, Irkutsk State University, 1, K. Marx, Irkutsk, 664003, Russian Federation, e-mail: hamoudadnan04@gmail.com 

Rasskazov Sergey Vasilyevich, Doctor of Sciences (Geology and Mineralogy), Professor, Head, Laboratory Isotopies and Geochronology, Institute of the Earth's Crust SB RAS, 128, Lermontov st., Irkutsk, 664033, Russian Federation, Head of Department of Dynamic Geology, Irkutsk State University, 1, K. Marx, Irkutsk, 664003, Russian Federation, tel.: (3952)511659, e-mail: rassk@crust.irk.ru 

Chuvashova Irina Sergeevna, Candidate of Sciences (Geology and Mineralogy), Researcher, Institute of the Earth's Crust SB RAS, 128, Lermontov st., Irkutsk, 664033, Russian Federation, Associate Professor, Irkutsk State University, 1, K. Marx, Irkutsk, 664003, Russian Federation, e-mail: chuvashova@crust.irk.ru 

Tregub Tamara Fedrovna, Candidate of Sciences (Geogaphy), Senior Researcher, Institute of Geology, Voronezh State University, 1, University sq., Voronezh, 394018, Russian Federation, tel.: 8(473)220-82-91, e-mail: ttregub108@yandex.ru 

Volkov Maxim Andreevich, Postgraduate, Voronezh State University, 1, University sq., Voronezh, 394018, Russian Federation, tel.: 8(473)220-82-91, e-mail: 1994vomaan@mail.ru 

Kulagina Natalia Valentinovna, Candidate of Sciences (Geology and Mineralogy), Researcher, Institute of the Earth’s Crust SB RAS, 128, Lermontov st., Irkutsk, 664033, Russian Federation, e-mail: kulagina@crust.irk.ru 

Kolomiets Vladimir Leonidovich, Candidate of Sciences (Geology and Mineralogy), Senior Researcher, Geological Institute SB RAS, 6a, Sakhyanova st., Ulan-Ude, 670047, Russian Federation, Associate Professor, D. Banzarov Buryat State University, 24a, Smolin st., Ulan-Ude, 670000, Russian Federation, e-mail: kolom@ginst.ru 

Budaev Rinchin Tsybikzhapovich, Candidate of Sciences (Geology and Mineralogy), Senior Researcher, Geological Institute SB RAS, 6a, Sakhyanova st., Ulan-Ude, 670047, Russian Federation, Associate Professor, D. Banzarov Buryat State University, 24a, Smolin st., Ulan-Ude, 670000, Russian Federation, e-mail: budrin@ginst.ru

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