Microbiota of the Barakun Formation and Biostratigraphic Characteristics of the Dal’nyaya Taiga Group: Early Vendian of the Ura Uplift (Eastern Siberia)

Abstract

The rich assemblage of Early Ediacaran (Early Vendian) acanthomorphic palynoflora (ECAP) was recognized in the middle part of the thick (2.2–2.7 km) clayey–carbonate sequence of the postglacial sediments of the Dal’nyaya Taiga Group (Ura Uplift). The degree of preservation of microfossils is determined by the instantaneous rate of their burial within the narrow facies zones of a deep-water basin, located at the base of large prograded carbonate bodies. The comparative analysis of microfossil remains from deposits of the Barakun Formation with the known Ura microfossil assemblage suggests that these assemblages belong to the unified complex palynozone within the Dal’nyaya Taiga Group. The comparative analysis of the Dal’nyaya Taiga assemblage with the Ediacaran palynofloras from other continents shows the high degree of diversification of microfossils, typical of the upper complex palynozones of the Lower Ediacaran of Australia and China, ascribed to the interval of 580–565 Ma. Thus, the greater part of the upper Dal’nyaya Taiga Group has a much younger age than was previously thought (<635 Ma). A noticeable reduction in the stratigraphic volume in most of postglacial deposits of the Dal’nyaya Taiga Group suggests the presence of significant stratigraphic hiatuses in the lower part of this sequence or the revision of the age of the Bol’shoy Patom glacial horizon.