Abstract

Devonian deposits are widespread within the boundaries of the Soviet Arctic. Geologically this territory does not represent a uniform region. It contains the Novaya Zemlya-Ural Caledonian-Hercynian fold area, the Severnaya Zemlya Caledonian fold zone; the Taimyr Hercynian subplatform trough; the Verkhoyansk-Chukchi Mesozoic fold area, the boundaries of which include the New Siberian Islands, and northern areas of the Siberian and Russian platforms.

This paper deals mainly with the Devonian deposits of the Soviet Islands as well as of Pay-Khoy Taimyr.

The Devonian is represented by marine, near-shore, marine, lagoonal and non-marine sediments, often interfingering both laterally and vertically, and forming complex sequences with varied lithological composition.

In areas predominantly underlain by carbonate rocks rich in fossils, stages may be distinguished with subdivisions into local stratigraphic zones. In areas underlain by carbonate-clastic sediments formations are recognized, and, more rarely, stages.

The lower boundary of the system is drawn tentatively at the base of dolomitic and gypsiferous strata, and the upper coincides with the top of the Cyrtospirifer tarandrus limestone.

Palaeogeographical analysis shows that the most favourable conditions for oil accumulation existed in the Middle and Late Devonian, when marine conditions of sedimentation prevailed. Gas and oil shows are ubiquitous in the Devonian deposits except for the highly metamorphosed zones of fold areas.

Favourable areas for oil accumulation are associated with clastic rocks, the permeability of which, in the Severnaya Zemlya Archipelago, is 300-600 m.d., as well as with zones of vuggy porosity and extensive fracturing in carbonate rocks. The most favourable oil and gas possibilities in the Devonian deposits should be in association with the northwestern part of Pioneer Island in the Hatanga Trough and in the New Siberian Islands. The Laptev Sea shelf is also of indubitable interest.