Abstract

The Devonian is widely distributed on the Russian and Siberian platforms and in the folded regions — the Urals, Caucasus, Tien Shan, Kazakhstan, Altai-Sayan, Taymyr, Verkhoyansk-Chukotsk, Mongolo-Okhotsk, etc. It is represented by marine, continental and volcanic formations.

The study of the fauna permits the discrimination of six palaeo-biogeographical provinces, belonging to two realms.

The lower boundary of the Devonian System is drawn at the top of the Tiverian, and at the base of the beds with Belgicaspis crouchi in Podolia, and of the Krekovian of Salair, and their stratigraphic analogues. This boundary needs to be defined more exactly.

The Lower Devonian is well represented in the carbonate facies of the Urals, Salair and southern Tien Shan, and in the terrigenous facies of Kazakhstan. It has only two subdivisions. It is the time-stratigraphic equivalent of the Upper Gedinnian, Siegenian and Lower Emsian.

The Middle Devonian is subdivided into Eifelian and Givetian. The Eifelian in Russia includes stratigraphic analogues of the Upper Emsian, because it contains both Early and Middle Devonian faunas. The Givetian is characterized by the development of Stringocephalus and Emanuella in the Atlantic palaeobiogeographical region.

Euryspirifer and Mediospirifer - faunas are developed in the Upper Givetian of the Pacific palaeobiogeographical region. These deposits are closely connected with the Lower Frasnian in a single sedimentary cycle.

The Upper Devonian is subdivided into the Frasnian and the Famennian, which in turn are subdivided into substages and zones. The upper boundary of the system is drawn above the Wocklumeria Zone. Correlation of the Devonian of the USSR, Western Europe and North America shows that the position of the boundaries of their series and stages, especially between the Silurian and the Devonian, needs reconsideration on the basis of the palaeontological and geological data.