Levels of planation in the mountainous terrain of the Bashkir Urals by the example of the Tukan area

During the geomorphological studies in the mountainous part of Bashkortostan, new data were obtained on the existence of two denudation levels corresponding to the geomorphological cycles of the Urals development in the Paleogene and Neogene, as well as at least four levels of the high-altitude planation in the Quaternary period. Presumably, the Kaga structural-denudation depression, the hypsometric position of which is 540-560 m, corresponds to the level of Miocene planation, and the pediments and pediplains of the upper tier of the relief (with absolute marks of 600-640 m) characterize the level of Oligocene planation. They are confined to the weathering crust with brown iron ore, gold deposits. A hypothesis is advanced that frost weathering and mountain glaciation in the Pleistocene and Holocene were the most important factors for the formation of flat tops of high mountain ranges and slope terracing. The obtained information is necessary for tectonic reconstructions, geological mapping, searches for ore-bearing weathering crusts, restoration of the history of development of the western slope of the Southern Urals.