Geomorphological Development of the Tunka Depression in the Baikal Rift Zone in Siberia, Russia

Abstract

There is no large lake, such as Lake Baikal or Lake Hovsgol, in the Tunka depression now, but it is one of the depressions of the Baikal rift zone. The bottom of the depression is formed of Miocene to Holocene rocks set on Precambrian and Paleozoic rocks, which mainly crop out in mountains north and south of the depression. In Miocene times, lacustrine sediments were formed and basaltic lava flows erupted. However, in the Pliocene and Pleistocene, fluvial or fluvioglacial sediments were formed. Therefore, it is assumed that the development of the Tunka depression is different from that of Lake Baikal and Lake Hovsgol. The difference has to do with the outflow of water via the Irkut river during the Phocene, Pleistocene, and Holocene. In the Phocene, any large lake apparently disappeared, because the sediments are composed of coarse sand and pebbles produced by the rivers. In the Pleistocene, many gravel beds were formed by fluvial and fluvioglacial processes, and, especially in the middle Pleistocene, water probably flowed out of Lake Baikal to the Irkut river via the Kultuk vafley (Kononov and Mats 1986; Mats et al. 2000).