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.
An integrated geological and geophysical study was performed to investigate the region of junction of the eastern part of the Central Asian Fold Belt and the Siberian Platform in the Skovorodino–Tommot 3-DV reference profile line (52°–60° N, 122°–129° E), where the belt is separated from the Aldan–Stanovoi Shield of the Platform by a series of deep faults. The main results are as follows: Seismic, density, and geoelectric characteristics of rocks were obtained and used to determine (refine) the intracrustal boundaries of tectonic structures; large-block structure of the Earth’s crust, caused by mantle faults, and the difference between the layered structure of the crust for the shield and fold regions were established; and available paleomagnetic data were used to perform palinspastic reconstructions for 180 and 140 million years, the most productive metallogenic epoch in the region, coeval with collision processes at the closure of the Mongol-Okhotsk paleobasin.
––In this paper we present a stratigraphic scheme for the subdivision and correlation of the Cambrian deposits in the south of the cis-Yenisei area of West Siberia, which was adopted as a current scheme by the decision of the Interdepartmental Stratigraphic Committee in 2018. This scheme is based on the data from stratigraphic test wells (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-1, Vostok-3, Vostok-4, etс.). In the study area, two structure-facies zones were identified: Kas (Lemok-1, Averinskaya-150, Tyiskaya-1, Vostok-4, and Eloguiskaya-1 wells), where sedimentary complexes accumulated in a salt subbasin, and Ket’ (Vostok-1 and Vostok-3 wells) with the deposition in an open sea basin. The boundary between these structure-facies zones is drawn along the inferred N–S-trending barrier reef zone. The rubrication in this paper is compiled in accordance with the requirements of the Stratigraphic Code of Russia for explanatory notes for regional stratigraphic schemes. Local stratigraphic subdivisions (formations, strata) are described and compared with the adjacent Turukhansk–Irkutsk–Olekma facies region of the Siberian Platform.
Fossiliferous Upper Vendian strata are discovered in the Upper Proterozoic to Lower Paleozoic Fore-Yenisei sedimentary basin under a thick Mesozoic–Cenozoic cover in southeastern West Siberia. Two depositional systems are recognized based on sedimentological features: (1) wave- and current-agitated shoreface–forereef–biohermal reef system (Vostok-3 Borehole section) and (2) tidal flat–evaporite basin (Averinskaya-150 Borehole section). The forereef facies yielded fossilized tubular calcareous skeletons of reef-building metazoans Cloudina riemkeae, Cloudina hartmannae and Cloudina carinata, phosphatized Namacalathus-like fossils, and a diversity of tubular phosphatized and agglutinated tubular fossils. The fossil assemblage can be interpreted as the evidence of ecological complexity of the reef system. Paleontological characteristics suggest correlation of the Vendian strata with the lowermost Purella antiqua Assemblage Zone and the boundary interval with the underlying Anabarites trisulcatus Assemblage Zone of the Siberian Platform. Therefore, at least in the late Proterozoic, the Fore-Yenisei sedimentary basin was part of a larger pericratonic depositional system on the western margin of the Siberian Craton.
The article presents results of specialized processing of the deep seismic profile along a part of Reference Profile 3-DV which crosses the Aldan-Stanovoi shield in the meridian direction and goes across its buried northern slope. The study is aimed at determining frequency-energy characteristics of the seismic wave field which are related to physical conditions of geological features of the crust. Based on analysis and interpretation of the dynamic profiles, it is possible to reveal and contour the Archean cores of consolidation of the Aldan shield and its buried continuation that is covered by sediments of the Middle Lena monocline and to input new facts in the proposed geodynamic model showing formation of the crust in the southeastern segment of the North Asian craton.
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