Paleogeographic History of Ancient Valleys of the Western Edge of the Baikal Depression

The article discusses published materials containing hypotheses about the history of the origin and development of ancient valleys within a relatively small area along the western edge of the Baikal depression. The results of geological surveys of various scales, carried out within the study area, are used. A comprehensive analysis of the materials reviewed has shown the inconsistency of the hypothesis about the young age of the ancient pra-Manzur valley and the catastrophic nature of this lake water drainage channel. The results of the author’s special narrow-focused studies have clearly established the existence of an ancient channel for the drainage of Baikal waters and indicated the location of the drainage cut. The study of the morphometric features of the pebble material, and structural and textural features of the sediments has shown that the Manzur alluvium was formed by a river comparable in size and hydrodynamic characteristics to the flow of the Angara River. The studies of the Manzur deposits conducted in recent years and their new multiple dating have confidently confirmed the time range of the functioning of the pra-Manzurka from the Early Pliocene up to and including the Early Pleistocene. The restructuring of the river network in the Central Baikal region that began in the first half of the Early Pleistocene led to the cessation of the pra-Manzur flow direction and the formation of new river systems within the Onot watershed: the Manzurka, Lena, Buguldeika, Goloustnaya and Anga. It has been established that the Buguldeika River formed its channel approximately 450 thousand years ago. According to biological data, the modern diatom community is very young; it began to form at the same time. The temporal proximity of this event in the biological history of the lake with the restructuring of the ancient river network is not accidental. Biological data confirm significant changes in the paleogeographic environment at this time. It is assumed that the formation of the paleodelta to the south of the modern delta of the Goloustnaya River may be associated with the paleo-Goloustnaya River, which could have begun to function immediately after the rupture of the pra-Manzur drainage channel and ceased its activity at the beginning of the Tyi phase of orogenesis.