Abstract

During the Middle and Late Devonian, on the site of the Urals and western margin of the West-Siberian lowland, the Ural geosyncline which had existed since the end of the Proterozoic continued its development. Within it a series of alternating narrow geosynclinal troughs and uplifts were formed. The western Ural sag and central Ural uplift were the outer parts of the geosynclinal system where sedimentary rocks accumulated. The more eastern zones of warping (Tagil - Magnitogorskaya and Alapaevscko-Bredl’skaya intergeosynclines) are characterized by active volcanic activity. Along the slopes of the eastern Ural and Tobol intra-geosynclinal uplifts which divided these zones, terrigenous and siliceous rocks, comprising the inner part, were formed.

In plan the longitudinal structural - facies zones have a beaded character controlled by the heterogeneity of that substratum on which the Ural geosynclinal system was founded. The most essential changes of structural-facies plan took place in Middle Devonian and pre-Frasnian time. They consisted in widening of zones of uplifts owing to the narrowing of zones of warping, displacement of the outer sag to the west and the involvement of the eastern margin of the Russian platform into the subsidence.

In the marginal parts of geosynclinal sags the amplitude of the final subsidence attained 3000 m., while in the pre-Urals it did not exceed 750 m.

In certain places the axial parts of positive structures experienced an uplift with an amplitude of more than 500 m.