Research subject. The most frequently utilized fundamental notions in stratigraphy are discussed: concrete section, composite section, the stratigraphic scale, the biochronologic scale, the International Stratigraphic Scale.

Materials and methods. The conventional content of these concepts is analyzed. The logical invalidity and negative consequences of the identification of subdivisions of the stratigraphic scale and subdivisions of a section are shown. The study of a section provides a way of obtaining information about the stratigraphic sequence of rock formation and the distribution of evidence of the events included in them, which are necessary for constructing stratigraphic scales. The close connection of the source of the actual data and results of its stratigraphic interpretation is the reason for the traditional identification of the subdivisions of the stratigraphic scale and subdivisions of a particular section.

Results. The biochronologic scale inherits from a section the time sequence of occurrences of species of a certain group of organisms selected as the basis of a scale. However, special features of the evolutionary development of organisms do not depend on the composition of the containing deposits and the method of the separation of sedimentary rock sequences. This development makes it possible during the study of many specific sections to establish homotaxis in the distribution of fossils, i.e., to build a biochronologic scale. Thus, the understanding of the scale is a model of the biochronologic calculation of geological time. Like any model, a scale cannot be identical to what it simulates.

Conclusion. A precise differentiation of the scale and a section is the basis for drawing correct stratigraphic conclusions. A zone is the smallest subdivision of the biostratigraphic scale. Zones are not divided into parts, are discrete (between adjacent zones there are no time passages), equivalent and are characterized by only the place which it occupies on the scale. The construction of a zone scale precedes the establishment of the material equivalent of the zone - of a stratozone - in the section. Any part of a stratozone is dated by the complete zone. The identification of the zonal scale with a sequence of stratozones in the section does not make it possible to understand the minimum dimensionality of a zone subdivision. The International Stratigraphic Scale (ISS) is defined, based on domestic stratigraphic codes and on foreign reference books, as a stratigraphic sequence of rocks (geological bodies) in total volume without passages and overlaps. In this treatment the ISS is not the scale, but is a complete (composite) geological section of the earth’s crust. The biostratigraphic scale serves as a tool of correlation. The ISS gives only the name of that subdivision, with which a concrete section is compared, and the geological age of the deposits of this section is designated by this name.

Research subject. In this study, the distribution of brachiopods in the Mid-Carboniferous boundary (MCB) sediments in the Middle and Southern Urals was investigated with the aim of determining the influence of the global Serpukhovian-Bashkirian minor mass extinction event on the diversity of these benthic organisms.

Materials and methods. Brachiopods distributed over the most complete carbonate sections of the West-Uralian (Brazhka, Sokol, Martyanovo, Askyn, Lakly), Magnitogorskian (Khudolaz, Kalinino, Bolshoy Kizil) and the East-Uralian (Beklenishchevo, Cave gully, Brod-Klyuchiki, “Uralnerud-1” quarry) megazons were studies.

Results. It was established that the diversity of the Giganto-productus-Striatifera brachiopod association reduced during the Late Serpukhovian, with the extinction of its dominant taxa having occurred during the Early and Middle Carboniferous boundary. During the Syuranian time of the Bashkirian Age, the Middle-Late Carboniferous Choristites association was formed. Further, in the Akavassian time, the diversity of brachiopods was restored. The consequences of the described event affected mainly the taxa of the species and genus taxonomic rank, and, to a much lesser extent, those of the family rank. On the western slope of the Urals, the maximum regression was recorded at the top of the Striatifera shell-rock layer of the Lower Carboniferous Staroutkinskian regional substage. On the eastern slope of the Urals, the brachiopod diversity characterizing the event in question can be clearly seen in the Late Serpukhovian. This dynamics was also manifested in the lowermost Pennsylvanian; however, it was obscured by the activation of regional tectonic factors.

Conclusion. In the Middle and Southern Urals, the Mid-Carboniferous minor mass extinction event is recognized according to the dynamics of the genus and species diversity of bra-chiopods in the deposits of different facies.

Research subject. In this paper, we consider specific features of the use of litho- and isotopic-geochemical data for the purposes of provenance reconstruction.

Methods and materials. The reconstruction tools under consideration included the analysis of the ratio of major oxides and variable trace elements, as well as the study of the distribution of trace elements. The research potential of these methods was illustrated using the data on the bulk chemical composition of sandstones and mudstones from the Bir’yan Member of the Upper Riphean Zilmerdak Formation, Upper Vendian Basa Formation (Southern Urals), Upper Devonian Kodinka and Ust’kodinka formations (Middle Urals), Lower Cretaceous Sortym Formation (Western Siberian sedimentary megabasin, Bolshekhetskaya depression).

Results. It was shown that the use of the vast majority of the described paired and triangular diagrams allows conclusions (consistent both with each other and conventional geological concepts) to be drawn about the composition of source rocks. These findings reinforce the insights gained from mineralogical and petrographic studies of sandstones.

Research subject. A section of the Upper Lochkovian (Lower Devonian) Valgan Formation located in the stratotypic area on the Ilych River, Northern Urals, was investigated.

Materials and methods. A study of the composition and structure of rock samples gathered from the section under consideration during fieldwork in 2015 was conducted.

Results. The studied section with an exposed thickness of 51 m is characterized by the thin and uneven alterations of calcareous con-glogravelites, coarse-grained and fine-grained organic sandsones, bioclatic-pelitomorphic limestones and argillo-calcareous shales. These rocks demonstrate a gradational and convolute lamination. An individual interval of the studied section contains calcareous conglobreccias layers. The Valgan Formation is characterized by a cyclic structure, with the thickness of individual cyclites ranging from 5.0 to 25 cm. The character of their structure testifies to sedimentation in slope settings. An analysis of clastic material revealed two sources of the basin area formation: near ablation (represented by the fragments of background bioclastic-pelitomorphic limestones) and remote ablation (represented by biohermal rock clasts). It is proposed to consider the Valgan Formation as the Valgan gradation, which extends the Upper Lochkovian sulfate-carbonate Subformation to the east.

Conclusions. Therefore, the Valgan gradation should be treated as an intermediate link between shallow-marine Upper Lochkovian biohermal structures and bathyal clayey and siliceous shales.

Research subject. The article presents the results of investigating calcite lenses with a cone-in-cone structure from Middle Devonian clay terrigenous deposits in the Middle Timan.

Methods. The investigation of petrographic thin-sections was carried out using a polarizing microscope Nikon eclipse LV100 ND equipped with a Nikon DS Fi2 camera. Polished sections etched with HCl were examined using a scanning electronic microscope JSM-6400 Jeol with a power dispersive spectrometer ISIS Link and a wave spectrometer Microspec. The decomposition of carbonates and the measurement of isotope carbon composition in the mode of continuous helium stream were carried out using a ThermoFisher Scientific analytical complex.

Results. It is established that the investigated calcite bodies consists of mosaic block crystals having a drusy structure. Calcite is characterized by abnormally low values S¹³C_carb - up to -23.5 %o. Clay films and soapstone inclusions were studied in detail. The formation mechanism of the saw-tooth profile of the upper bound of these inclusions was determined, which consists in the local substitution of alumosilicates with calcite under the maintenance of their relic layered texture.

Conclusions. A new version of the crystallization model of carbonate body genesis with a cone-in-cone structure is proposed.

Research subject. The Mamskay muscovite province (MMP) is located on the border between the Siberian platform and the Baikal orogenic area, near the boundary fault. The MMP hosts numerous regional and local thrust and reverse faults, which are typical of compression zones. This article aims to present a generalized description of the largest faults in the study area, to show their position in the regional structure of the province, as well as to consider their relationship with the main MPP tectonic stages, pegmatite and mica formation.

Materials and methods. The study was conducted on the basis of literature and archive data, as well as those obtained during the authors’ long-term research. The correlation between the formation stages of the MMP reverse faults and the dynamics of the compression zone formation was investigated using the methods of physical modelling at the Laboratory for Tectonophysics, Institute of the Earth’s crust of the Siberian Branch of the Russian Academy of Sciences.

Results. A comparison of experimental and field observations revealed the following six major stages in the evolution of the MMP fault tectonics: sedimentation, pre-pegmatite inversion or collisional-folded, early pegmatite, late pegmatite, post pegmatite and neotectonic. These stages were linked with the processes of folding, magmatism, pegmatite and mica formation.

Conclusions. It was established that the formation of reverse faults and thrusts in the MMP resembled the process of fracturing in compression zones. The pegmatite-controlling role of the thrusts and reverse faults is determined by their age relations with the stages of the pegmatite and mica formation process. The main types of the mica-rich pegmatite fields in the MMP fault zones, which were mapped during geological survey studies, were distinguished and characterized.

Research subject. In this research, volcanoplutonic formations (VPF) in the Baleisky ore node (BON) consisting of intrusions of the Amudzhikan-Shakhtama complex (J2-3) and comagmatic effusions of the Shadaron series (J2-3) were investigated.

Methods. Investigations were carried out in the analytical center of the SB RAS Geological (Ulan-Ude). Silicate analysis was performed by the conventional method. Ore and rare elements were determined by the RFA method. Rare earth elements were detected using the ASP-AES method.

Results. It was determined that VPF in the BON has a zonal structure. In the central parts of the BON, granite rods of the Amudzhikan-Shakhtama complex (J2-3) are located. Further, moving from the central BON parts towards its periphery, a belt of small intrusions of the Amudzhikan-Shakhtama complex (stocks of monzonite diorites, granodiorites, dikes of diorite porphyrites, lamprophyres) is located. The majority of gold deposits and ore occurrences are confined to this zone. The peripheral parts of the BON feature volcanogenic sedimentary deposits of the Shadaron series (J2-3). In composition, these deposits correspond to island-arc and post-col-lisional formations. It is shown that the intrusions of the Amudzhikan-Shakhtama complex correspond to high-potassium calc-alkaline series.

Conclusions. It was found that the magmatic melts of the Mesozoic ore-bearing intrusions located in the Baleisky deposit area are more differentiated and located at lower depths compared to the rocks of similar composition in other BON parts.

Research subject. The object of the study is the littleknown earthquake of 1829 in the North of European Russia on the average course of the Northern Dvina River (Arkhangelsk district). This event is included in domestic seismological catalogs, but without reliance on primary written sources.

Materials and methods. The materials laid by the authors of the study include publications in periodicals immediately after the event, additional information from the local edition of 1864, as well as images of local religious buildings that experienced tremors, i.e. a variety of previously not involved macroseismic information.

Results. Based on the new information, estimates of the strength of the tremors of 3 shocks in points were carried out according to the MSK-64 scale, and the main procedure was used to determine the main focal parameters of each shock. The epicenter is relocated, the macroseismic event field is presented. The intensity of the main shock VI or VI+ points.

Conclusions. The results are new and more representative than those available to seismologists before. In addition, new macroseismic data were compared with young faults, as a result of which the genetic connection of the earthquake with a large active fault under the valley of the Severnaya Dvina River was determined. This establishes the possibility of moderate earthquakes not only on the Fennoscandinavian crystalline shield and in the folded structure of the Urals, but also in the North of the East European platform.

Research subject. The paper describes large tectonic zones in the North Caucasus, which can be classified as deep faults according to a number of features. Among these formations are the Ancient axial fault zone earlier described by G.D. Azh-girei, which we attributed to Hercynian structures (with the presence of pre-Paleozoic); the Indosinian axial fault zone and the Main Caucasian fault (overthrust).

Materials and methods. The Ancient axial fault zone is considered as a suture zone, which arose as a result of Varisсan (Hercynian) folding during the interaction of the Transcaucasian and East European tectonic plates (EETP). The Indosinian axial fault zone contains fragments of Variscan nappes and neoautochthonous deposits of the same age.

Results. The surface manifestation of the Indosinian axial fault zone was a tectonic-formational zone of the Front Range, which is located at the junction, on one side, with the newly formed hard crystalline massif crust at the site of the Ancient zone (Main Range), and, on the other side, with EETP. This zone continued to be active later, during the Cimmerian and Alpine tectonic events. At the same time, the formation of new granite magmatic melts could occur. The driving mechanism is assumed to have been opposite undercrust convection flows. Although there are conflicting views on the Main Caucasian fault, it seems clear that this was a deep-seated and magma-producing zone at the pre-Callovian time. This fault is likely to have been formed as a consequence of the intraplate subduction, which is continuing at present.

Conclusions. The presence of hyperbasite bodies in the fault zones under consideration is not a sign of their depth in the Caucasus. In the present structure, the mixtite zone lying under the flysch of the southern slope of the Greater Caucasus and overlapping the Transcaucasian massif can be considered as a large collision line currently under development. Some other faults present in the region, which are supposed to be deep, have also been considered.

On December 8, 2019, Anatoly Ivanovich Rusin, a well known specialist in Petrology and Geochemistry of metamorphic complexes, doctor of geological and mineralogical Sciences, and Professor, died.