Abstract

The Devonian is widespread in the northeastern part of the USSR and is represented by all three series. The region may be separated tectonically into three parts, resulting in the formation of sediments of different composition and thickness. Mio-geosynclinal conditions of sedimentation existed over the largest part of the territory. In the Devonian, the Kolyma, Omulevsk and Ikhotsk massifs were subjected to intensive warping, accompanied by volcanic activity. In the basins of the Penzhino river and of Anadyr and in the region of Koryak Ridge, sediments of eugeosynclinal type were deposited.

The more complete sections of the Devonian are found in marginal uplifts of the Kolyma median massif and in Sette-Daban. The marine, carbonate and terrigenous sediments (up to 2000 metres) gave way in places to lagoonal deposits (gypsum, anhydrite). The Lower Devonian is subdivided into the Tikhiyruchei and Belyak units. The Eifelian includes the Vecherniy and Urultun units. The Givetian is characterized by limestones with Stringocephalus burtini, dolomites, gypsum and anhydrite. In the basal Frasnian there occur beds with Mucrospirifer novosibiricus, followed by beds with Pharciceras timanicus, Calvinaria biplicata, succeeded in turn by beds with Theodossia ex gr. anossifi. The Famennian is subdivided into beds with Gastrodetoechia muolensis, Leiorhynchus ursus below and beds with Cyrtospirifer kurban above.

The Devonian of northeastern USSR is closely related to that of the Soviet Arctic, the Siberian platform, Alaska and northwestern Canada. Thus we can suppose that in the Devonian these marine deposits belonged to a single Arctic palaeozoogeographic province, which was connected with the Ural-Tien Shan palaeozoogeographic province through Novaya Zemlya.