Abstract

In the Altai-Sayan region the Devonian deposits together with those of the Carboniferous and Jurassic occupy Tuva, Uimen, south and north Minusinsk, and Rybin intermontane areas and some small, superposed troughs and grabens.

The Devonian deposits rest upon complexly folded and faulted Lower Palaeozoics and are crumpled into simple punch folds. From south to north the thickness of the section decreases from 10 to 3 kilometres.

The characteristic feature of the Devonian of the intermontane areas is the rhythmic nature of the section, which is expressed in the alteration of thick red terrigenous and effusive strata of continental origin with variegated and gray terrigenous marine carbonate deposits of lesser thickness or of deposits of intercontinental seas or lakes.

Three divisions of the Devonian are distinguished, subdivided into stages and even into horizons. The last include coeval suites of different facies of various intermontane areas.

The marine deposits are known from the Eifelian (Tashtyp horizon) and from the upper part of the Givetian (Bei horizon). The Tashtyp transgression spread from Mongolia and embraced south Minusinsk, Uimen, and the south part of Tuva. The Bei transgression reached the north Minusinsk area. In other regions, lagoonal and continental deposits were accumulated.

The Tashtyp horizon may be correlated faunally with the Shanda horizon of the Kuznetsk basin and probably with the Onondaga Formation of North America. The Bei horizon is correlated with the Hamilton Formation of North America.