The stratotype and facies of the glacial Lower Vendian Nichatka Formation, Chara River basin, Central Siberia

摘要

Sediments of the Nichatka Formation are facially studied and thoroughly described, the sections are correlated, and the subformations are recognized. The formation represents a key stratigraphic unit to reveal the origin of the Central Siberian glacial horizon and to correlate it with glacial horizons in other regions of the world, namely, with the Laplandian Horizon of the Lower Vendian, Nantou and Marino tillites, etc. The Nichatka Formation is correlated with the glacial Bolshoi Patom (Dzhemkukan) Formation of the Vendian reference section at the Ura Uplift. Unlike the latter, it is mainly composed of continental glacial deposits and is marked by a complex facies composition. The glacial origin of the Nichatka Formation is reliably determined on the basis of a set of diagnostic characters. This permits a more complete reconstruction of the Early Vendian depositional environments. In addition to typical basal tillites and marginal moraine deposits, the formation includes glaciolacustrine and fluvioglacial sediments along with aquatillites, allotillites, and the glacial fan, including subaqueous, deposits.