Article: Biostratigraphical implications of a Chuaria–Tawuia assemblage and associated acritarchs from the Neoproterozoic of Yakutia

A new occurrence of the carbonaceous fossils Chuaria circularis and Tawuia dalensis is reported from subsurface Neoproterozoic in the Khastakh 930 Borehole in the Lena-Anabar Depression, northern Yakutia. Neoproterozoic deposits in this region are regarded as belonging largely to the Yudomian Stage. There have been no faunal records from this site and the strata directly underlying fossiliferous Permian deposits are, on lithostratigraphical grounds alone, regarded as Cambrian. Preliminary palynological results here can be compared with other Neoproterozoic (late Riphean) occurrences of large and morphologically complex acanthomorph acritarch taxa such as Trachyhystrichosphaera vidalii. This biostratigraphically diagnostic taxon is associated with vase-shaped fossil protists and other diagnostic acritarchs also known from Upper Riphean strata elsewhere, placing this Chuaria circularis-Tawuia dalensis assemblage within the time interval of around 840-700 Ma. By comparison with other regions, the recovered fossils appear to indicate that the investigated succession is of Neoproterozoic (Late Riphean) age, thus preceding the Varanger glacial event.