Pre-Vendian Unconformity and Sedimentation during Late Cryogenian Glaciation: Structural Relation of Sedimentation Events in the Southwest of the Siberian Platform

The relation of sediments and their associations is considered for the lower part of the Early Vendian (Late Cryogenian) Marnya Formation of the Oselok Group of the Sayany sedimentary basin of the Siberian Platform. The main method of comparison of genetically diverse sediments includes the lithofacies analysis and correlation of successive cross-sections, which link the sediments into the systems. Four sedimentation stages are identified in the Late Cryogenian (Early Vendian) glaciation: (1) permafrost and thermal karst, (2) glaciation, (3) primary thawing of the glacier and formation of the upper glacier stagnant lakes with a package of cap dolomites, and (4) full regional thawing of the glacier and formation of fluvioglacial fans. The key correlation elements include the kurum breccias, which formed at the first stage as a result of the uplift of the paleocontinent and its “dry” freezing, and tillites formed during its glaciation. The pre-Vendian unconformity formed in several stages: general rise and areal denudation of the craton, sliding of kurums, thermokarst dissolution of the Riphean carbonate rocks, glacier exaration, and erosion by glaciofluvial river flows. The deposits of the carbonate platform, which overlaps glaciofluvial fans, are ascribed to the Ediacaran global deglaciation and eustatic uplift of ocean level.