Late Precambrian and Early Cambrian in the East European platform

In recent years the problem of the Cambrian—Precambrian boundary has again attracted the attention of a large number of geologists both in the U.S.S.R. and elsewhere. The study of regions with perfect outcrops of stratigraphically complete sections of Vendian—Cambrian deposits is of great importance for the solution of this question. The Baltic area is one such region in the East European platform.

In the eastern part of the Baltic region, the transgressive Vendian complex rests with conspicuous unconformity on the crystalline Precambrian basement. Vendian rocks form a structurally complex cycle of sedimentation and include the Merkine, Gdovsk and Kotlin (Vilkiškiai) Formations. Rocks with similar lithofacies underlie regions of northern Byelorussia (the Orsha depression) and the Brest and Moscow depressions. These rocks are comparable, not only in lithology, but also in mineralogical composition and the occurrence of distinctive assemblages of problematic microfossils.

During Early Vendian times the epicontinental basin of the East European platform had a connection with the then existing basins of Volhynia, Podolia and Moldavia and with the southeastern part of Poland.

It is worth noting that in almost all sections of the East European platform a weathering crust had developed before the start of Vendian sedimentation, in connection with basin regression at the end of the Kotlinian time interval. After regional erosion, the Vendian deposits were overlain by palaeontologically well-defined sediments of Lower Cambrian age containing microproblematics and fragments of Sabellidites, Yanichevskyites and Platysolenites. These beds are overlain by trilobite-bearing deposits.

During the Lontova time interval the epicontinental basin of the East European platform had advanced in the form of gulfs from the Moscow depression to the eastern part of the Baltic region. In the northeastern area of the Moscow depression the preserved thickness of the Lontova deposits exceeds 250 m, while in the Baltic regions it averages 0–125 m.

The stratigraphic correlation scheme shows that a biostratigraphic boundary at the base of the transgressive sandstones of the Lontova Formation coincides with the Vendian—Cambrian boundary as defined by lithological data, and also with a conspicuous appearance of glauconite and skeletal remains.