Abstract

The composition, thickness, facies character and palaeontological remains oi the Devonian of the western slope of the Urals are structural - facies effects of conditions which existed during the Devonian in the outer part of the Ural geosyncline system and of the adjoining margin of the Russian platform.

The lower division, in places subdivided into Gedinnian and Coblenzian stages, is represented in the Belsko-Elets facies area.

The middle division, which is fully represented in the Belsko-Elets area, is subdivided into two stages. The lower stage (Eifelian) includes the Takatin, Vyasov, Koyven and Biysky horizons, while the upper one (Givetian) includes the Afonin, Chusov and Cheslav horizons. In the Sakmir-Lemvin area only the Eifelian Stage is present, whie in the Zigan-Visher area and at the Chernychev ridge the Middle Devonian is absent from the section as a result of pre-Frasnian erosion.

The upper division, subdivided into Frasnian and Famennian stages, extends over three areas. The Frasnian Stage includes the Oashiy, Kynov, Sargaev, Semuluk, Mendym and Askyn horizons. The Famennian Stage is sometimes subdivided into the Makarov, Mursakaev and Kushelgin horizons.

In the Belsko-Elets area the Devonian sediments of the western slope of the Urals are represented by carbonate deposits having a thickness of 3000 m.; in the Zigan-Visher area and at the Chernyshev ridge by carbonate rocks, with subordinate sandstones and shales, attaining a thickness of 1000 metres; and in the Sakmar-Lemvin zone mainly by sandstone, shale and carbonate formations 1000 m. in thickness.