Neoproterozoic Chingasan Group in the Yenisei Ridge: new data on age and deposition environments

Trachybasalt-alkali trachyte volcanism in the Yenisei Ridge was found out to be synchronous with deposition of coarse tilloids and flysch of the Chivida Formation of the Neoproterozoic Chingasan Group. New 703±4 Ma ⁴⁰Ar/³⁹Ar biotite and titan-augite ages of subalkaline basalts in the Chivida Formation indicated that they erupted in the Late Neoproterozoic. According to microfossil evidence, the Chingasan sediments correlate with Late Neoproterozoic strata in the type sections of the southern Siberian craton. The Chingasan deposition apparently lasted no longer than 30 Myr judging by the isotope ages obtained for the underlying Upper Vorogovka Group and subalkaline basalts in the Chivida Formation. The fault-parallel position of grabens and coarse grain sizes and variable thicknesses of their lithological complexes, as well as syndepositional trachybasalt-alkali trachyte volcanism provided evidence that the volcanosedimentary rocks of the Chingasan Group formed in an environment of active rifting.     

Tappania-bearing association of the Siberian platform: Biodiversity, stratigraphic position and geochronological constraints

A new fossil microbiota yielding eukaryotic Tappania is described from the Mesoproterozoic Kamo Group of the Central Angara Basin, Siberian Craton. The assemblage also includes Valeria, Satka, Lophosphaeridium, Pulvinosphaeridium, Miroedichia, Osculosphaera, Tasmanites, Obruchevella, Glomovertella, as well as branching and anastomosing filamentous microfossils of putative fungal affinities and peculiar short trichomes, that together substantially increase the biodiversity of the Tappania Association. Stratigraphic position and geochronological constraints indicate a relatively young Late Mesoproterozoic age of the Tappania-bearing sediments. There appears to be a continuity between the Tappania Association and the Neoproterozoic microbiota, the latter being firmly rooted in the Late Mesoproterozoic.     

A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3)

The Borehole Vostok 3 drilled in the east of the West Siberian Plate (Tomsk Region) revealed a Vendian section in the depth range 5002–3870 m, which was subdivided into the Poiga, Kotodzha, and Raiga Formations based on geological, geophysical, and paleontological data. In the Kotodzha and Raiga Formations, typical Upper Vendian fossils of Cloudina hartmanae and Namacalathus sp. were found along with diverse Platysolenites, which are commonly considered to be of zonal significance in Lower Cambrian strata. Hence, the stratigraphic interval with abundant diverse Platysolenites has a wider stratigraphic range than it was believed earlier and seems to cover the Upper Vendian and Lower Cambrian deposits. The Borehole Vostok 3 is the first Siberian occurrence of the fossils Namacalathus, the world's fourth occurrence of the Cloudina-Namacalathus association, and the first site where coexisting Platysolenites and typical Vendian organisms have been found. Therefore, the borehole provides one of the most informative (in paleontological context) Upper Vendian sections.     

Stratigraphic setting and age of the complex Tappania-bearing Proterozoic fossil biota of Siberia

A microfossil assemblage has been found in the widely spaced (300 km apart) Baikit and Katanga areas (inner Siberian Platform) in stratigraphically coeval strata in the lower part of the petroliferous Kamo Group (Riphean). It comprises complex protists Tappania plana Yin; acritarchs Valeria lophostriata Jank., Satka sp., Lophosphaeridium sp., Pulvinosphaeridium sp., and Miroedichia sp.; porous vesicles of Tasmanites sp. and Osculosphaera sp.; vesicles with anastomosing processes, and spiral filaments of Obruchevella and Glomovertella. Siberian fossil microbiota is considerably more diverse than biota with Tappania protists known in Australia and China. A taxonomically similar fossil biota found 1500 km northeast of the well-studied Riphean section in the Olenek uplift suggests that the host rocks, too, are stratigraphically coeval. This permits refining the age of remains of the first complex eukaryotes from the inner platform and is an additional correlation criterion for the lower Kamo Group.     

Rb–Sr Age of Riphean Glauconites of the Kamo Group (Baikit Anteclise,Siberian Craton)

Doklady Earth Sciences - A mineralogical-geochemical study of globular phyllosilicates (GPS) of the glauconite-illite series of the Dolgokta Formation from the stratigraphic well Chunkinskaya Well...