The study of stratigraphy and paleontology of the Riphean/Vendian boundary strata is fundamental to decoding the transitional (Neoproterozoic) stage in the evolution of the biosphere. During this stage, the Pro-terozoic-style biota with limited morphological diversity, small size of individual organisms, lack of biogeo-graphic zonation, and low rates of evolutionary turnover was replaced by the diverse Phanerozoic-style biota, with bioprovinciality and high dynamics of mac-roevolutionary processes . The study of the transitional period invokes the analysis of the most representative Upper Proterozoic sections along the periphery of the Siberian Craton. Here, the uppermost Riphean was separated into the Baikalian Complex , which was proposed as a Regional Stage or, later, as an Erathem of the General Stratigraphic Chart for the Pre-cambrian of Northern Eurasia and equivalent to the Cryogenian of the International Stratigraphic Chart for the Precambrian. Ediacaran fossils recently discovered in the Ui Group suggest that the biosphere shift commenced during the Baikalian.
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