The Precambrian – Cambrian Boundary and Principles of Its Justification in Siberia

An all-Siberian biostratigraphic scheme of the Vendian-Cambrian beds is discussed in the paper. It is based on new data pertaining to the distribution of small-shelly fossils in the reference sections of transitional and eastern facies areas on the Siberian Platform. The lower boundary of the Cambrian is suggested to be placed at the base of the A. sunnaginicus zone, whose volume is given more precisely. It is shown that a larger volume of the zone in the eastern facies area is due to the sharpest predominance of its typical forms in the upper Tommotian stage rather than to the addition of more ancient beds. This new biostratigraphic scheme of Siberia is well correlated with the Chinese biostratigraphic Vendian – Cambrian zoning, and the lower boundary of the Cambrian coincides with the marker “B” point in the Meishucun section. Comparison of the biostratigraphic subdivision of the Vendian – Cambrian sediments based on small-shelly fossils and other groups of organic remains clearly shows that the former are obviously more advantageous.