The Angarian in the Yenisei Ridge as a standard Neoproterozoic unit

The Late Neoproterozoic sediments of the Yenisei Ridge formed in several isolated basins. These sediments are correlated, and the composite section of this age in the region is described. Two age limits are of extreme importance: pre-Chapa (650 Ma) and pre-Vendian (600 Ma). The former, observed in a much larger area, predominates. The great importance of the pre-Chapa transformation becomes evident owing to its coevality with the Marino-Nantuo global glaciation and the preceding tectonic events. This glaciation was immediately followed by a significant biotic event that gave rise to the Doushantuo-Pertatataka microfossil assemblage and, afterward, Ediacaran fauna. The Chapa Group is proposed as a prototype of the Angarian—a unit of the General Late Precambrian scale, which is of the same rank as the Vendian. According to these data, the main Late Neoproterozoic units are the Baikalian, Angarian, and Vendian.