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Abstract

Ordovician rocks are widely represented in the Soviet Arctic. They are known in Novaya Zemlya, Vaygach Island, Pay-Khoy, Severnaya Zemlya, the northern Siberian platform, the New Siberian Islands, and the northeastern USSR. In the western Arctic (Polar Urals-Novaya Zemlya), Ordovician deposits are represented by a very thick and varied complex of clastic-carbonate rocks.

The Ordovician is at the base of the stratigraphie column in Severnaya Zemlya; on Taymyr Peninsula and on the Siberian platform, the Cambrian and Ordovician rocks form a continuous sequence. Ordovician deposits in the region are represented by predominantly carbonate rocks as thick as 2,000 m in basins; in the northern part of the Taymyr Peninsula, the Ordovician consists of clastic-carbonate rocks as thick as 1,000 m containing graptolites. The Ordovician of Severnaya Zemlya is represented by variegated clastic-carbonate rocks about 2,000 m thick.

Within the eastern Arctic, Ordovician deposits are a part of the folded margin of the Kolyma massif and the Mesozoides of the northeastern Chukotsk Peninsula. Ordovician strata in the northeastern USSR are represented by carbonate, clastic-carbonate, and clastic sequences. The relations with underlying rocks are uncertain. Thicknesses are widely varied and reach 5,500 m in places.

Ordovician deposits have been studied in more detail in southern Novaya Zemlya, Vaygach Island, northern Pay-Khoy, central Taymyr, in the district of Noril'sk, and within the limits of the folded margin of the Kolyma massif. The Ordovician of northern Novaya Zemlya, Severnaya Zemlya, and the New Siberian Islands is less well known.

Even where Ordovician sections have been investigated comprehensively and are richly fossiliferous, however, the Lower-Middle Ordovician and Ordovician-Silurian boundaries are uncertain because of geologic peculiarities of the region, and no definite solution to the Cambrian-Ordovician boundary problem has been found. Varied sedimentary facies and diverse Zoogeographie provinces make regional and interregional correlations difficult. Nevertheless, recognition of transitional sequences in fold areas of the Soviet Arctic and the wide interregional distribution of some faunal elements during climaxes of marine transgression (late Tremadoc and middle Caradoc) permit rather definite correlations for the solution of practical biostratigraphic problems and correlation with standard sequences elsewhere.

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