Abstract

A re-examination is currently being carried out in Europe and America on the boundary beds of the Silurian and Devonian Systems in Germany, Czechoslovakia, Poland, USSR, Morocco and Canada through conferences and international symposia. Many of these sections, however, are situated in folded regions, characterized by tectonic dislocations and stratigraphic breaks, therefore there is no certainty in their sequence and continuity.

There is, however, a section of the Silurian in Podolia, in the southwest of the USSR, which can be interpreted as the most complete in Europe. These Podolian deposits are characterized by an essentially undisturbed, continuous section of quiet-water deposits having an abundance of organic remains. They have a total thickness of about 850m. The Dniester Valley, crossing at right angles to the strike, exposes a complete section of Middle Llandoverian to Lower Devonian inclusive. Changes of facies can be traced along the strike for a distance of about 100 km. This section is considered to be the key section for European Russia, and as such may be used for the definition of the stage divisions of the Silurian and also of the boundary between the Silurian and Devonian in the USSR.

Detailed lithological and bio-stratigraphic investigations were carried out between 1963 and 1965 by the personnel of the All-Union Geological Institute (Leningrad), who have succeeded in working out a detailed description of this comprehensive section. Additional collections of Stromatoporoidea, Tabulata, Rugosa, Brachiopoda, Pelecypoda, Cephalopoda, Bryozoa, Tentaculitidae, Trilobita, Ostracoda, Eurypterida, Crinoidea, Graptoloidea, Fishes and plant remains were collected and are now being studied.

The detailed study of this succession of faunal assemblages in a fully exposed, unbroken, and tectonically undisturbed Silurian section makes possible a clear definition of the Siluro-Devonian boundary, which can be recognized in countries outside the Soviet Union.