卷 31, 编号 2 (2023)

The values of Ni/Co, La/Sc, and Th/Cr (indicators of the composition of rock complexes eroded in paleowatersheds) and the values of CIA, Rb/Al, K/Al and K/Rb (indicators of the intensity of chemical weathering on land), typical for fine-grained clastic rocks of the Riphean of the Southern Urals were compared to the data given in the publication “Long-term evolution of terrestrial weathering and its link to Earth’s oxygenation” by Bayon G., Bindeman I.N., Trinquier A., Retallack G.J., and Bekker A. (Earth Planet. Sci. Lett., 2022, v. 584. 117490). It was shown that the average Rb/Al ratio (0.0014 ± 0.0006, n = 66) typical of the Riphean clayey rocks of the Southern Urals, together with other data, suggests that for more than 1.10 Ga (from ~1.75 to ~0.60 Ga) the intensity of chemical weathering in paleowatersheds was relatively low. This is in good agreement with the data obtained by Bayon et al. The material presented in the article allows us to consider that the composite “world” curves of K/Al, Rb/Al, and K/Rb by Bayon et al. and the same curves for clayey rocks of the Riphean of the Southern Urals are sufficiently comparable. Thus, data on the lithogeochemical characteristics of fine-grained clastic/clayey rocks of the Riphean stratotype significantly expand our understanding of the nature of chemical weathering processes on land in the interval 1.75–0.60 Ga ago.

The paper deals with the composition and stratigraphy of the evaporite formation in the salt-producing province of the Caspian region. Based on seismostratigraphic approach, the correlation of geological sections in the lateral areas of the salt-producing province with the halokinetically deformed sections in the central areas of the Preсaspian depression is proposed. As a result of the research, a new local stratigraphic scheme of the Permian evaporite formation of the Central subprovince is proposed and the principles of its construction using the results of the seismostratigraphic analysis of the Asselian-Tatarian seismogeological substage and the accepted serial legends of three groups of sheets of geological maps (scale 1 : 1000 000; Scyphian (South-European), Central-European, and Uralian maps) are outlined. The results obtained significantly clarify the known schemes of the oil and geological zoning of the Caspian oil and gas province and contribute to the development of the resources of the deep (subsalt) horizons of its sedimentary cover.

The study of new sections of the upper part of the Upper Volgian substage near the Vasilyevskoye village (R-ybinsk district, Yaroslavl region) made it possible to clarify the position of the lower boundary and the infrazonal division of the Volgidiscus singularis Zone. Until recently, the lower part of the Singularis Zone was not characterized by ammonites, but thanks to the study of these sections, it was possible to establish the sequence of craspeditins ammonoids (Volgidiscus and Anivanovia) and to identify a new biohorizon Volgidiscus cf. lamplughi. The lower boundary of the Singularis Zone in the Chudinovskaya Formation sections is determined by the first appearance of Volgidiscus above the Craspedites milkovensis biohorizon. The infrazonal volume of the Singularis Zone is represented by three biohorizons: V. cf. lamplughi, V. pulcher and V. singularis. At present, the Singularis Zone is characterized by the most complete structure in the Panboreal Superrealm, which allows it to be considered as an infrazonal standard for the upper part of the Upper Volgian substage.