Research subject. Research articles and notes on stratigraphy, paleontology, paleomagnetism, lithology, and geochemistry of Riphean sedimentary rocks of one of the largest structures on the western slope of the Southern Urals – the Bashkir mega-anticlinorium, published during the period from 2010 to October, 2024 and available at the Scientific Electronic Library on the eLIBRARY.ru platform.

   The Riphean sections of the western wing of this mega-anticlinorium were accepted by N.S. Shatsky as a stratotype for the Riphean group.

   Materials and methods. An analysis of new facts, ideas, and hypotheses on the stratigraphy, lithology, and formation conditions of terrigenous and carbonate sequences of the Riphean obtained as a result of long-term studies of a large group of authors was performed. New data on the geochemistry
of Riphean sedimentary rocks, the isotopic composition of oxygen, carbon, and nitrogen in carbonate rocks, as well as the geochemistry of the associated manifestations of organic matter were considered.

   Results. The conducted review of research on various aspects of the Riphean geology of the Bashkir mega-anticlinorium, available at the eLIBRARY.ru platform, has revealed a large number of works published over the last 15 years. Some of these works are devoted to specific issues and facts, while others open new pages in the history of research into the geology of the Bashkir mega-anticlinorium.

   Conclusions. The critical analysis of publications on the Riphean geology of the Bashkir mega-anticlinorium provides a clear picture of contemporary achievements in the field of stratigraphy, paleontology, and paleomagnetism, as well as lithology and geochemistry of sedimentary rocks. In many respects, these studies are conducted at the international level; however, some areas require special support and care in order to be continued.

   Research subject. Issues related to the chronological representation of time in stratigraphy are discussed, including the features of biochronological calculation of geological time, the nature of zonal biochronological scales, the dual nature of stratigraphic classifications, the biological basis of chronostratigraphic divisions, as well as the concepts of “chronological
scale” and “chronological classification”.

   Material and methods. Conventional approaches to the above issues are analyzed. An attempt is made to reveal the logical sources of disagreement on the issues under discussion and to outline possible compromise solutions.

   Results. In order to successfully resolve the abovementioned issues, it is necessary to distinguish the biochronological scale as an instrument for measuring geological time and the geological section – as an object of measurement. Being cycles of paleontological development, peer subdivisions of biochronological scales should be equivalent, but not stratigraphic subdivisions of the same order.

   Conclusions. The true chronological scales in stratigraphy are zonal biochronological scales, the construction of which uses the evolutionary sequence of similar events (“existence of species”), which allows us to obtain a scale of order consisting of equivalent (commensurate, equivalent, congruent) divisions – zones. The International Stratigraphic Scale (a summary section of the stratisphere) is, in its essence, a calendar of geological events and dates. The names of the subdivisions of the International Stratigraphic Scale serve as an international chronological language.

   Research subject. The southeastern part of the Siberian Platform which is adjacent to the zone where the reference profile 3-DV Tommot–Khandyga runs.

   Aim. To analyze and inteprete new and published geological, geochronological, and geophysical data, as well as presenting the most recent data on tectonics and deep structure of the large basement blocks of the southeastern Siberian Platform based on the new tectonic map of the Lena-Aldan rift zone.

   Materials and methods. Using geophysical techniques, a number of large features were identified under the sedimentary cover varying in thickness from 0.5 km to 3 km, which form the southern part of the extended Lena-Aldan paleorift zone and interpreted as giant stratified basite-hyperbasite abyssolites and alkaline-ultrabasic intrusives emplaced in the Proterozoic as a result of mantle plume magmatism.

   Results. Fundamentally new data were obtained on tectonics and deep structure of the crystalline basement in the southeastern part of the Siberian Platform within the zone of the 3-DV Tommot–Khandyga reference profile and the adjacent areas. A tectonic map of its basement is proposed.

   Conclusions. A high level of knowledge derived from comprehensive geological and geophysical studies within the 3-DV reference profile zone allows us to accept the obtained results and conclusions as a working hypothesis for further medium- and large-scale geological studies and prognostication. The Lena–Aldan rift zone is ranked as a highly productive mineragenic province indicating favorable potential for nickel, copper, chromium, platinum group metals, vanadium, rare earths, and rare metals, which makes it a homologue of the unique Transvaal province of South Africa in terms of its ore potential.

   Research subject. Cyanobacteria and biogenic ultramicrostructures in stromatolites.

   Aim. Analysis of methods based on the systematization of stromatolites according to morphological characteristics, as well as the results obtained using these methods. Justification of the need to continue the study of stromatolites. Description of a method for detecting microbial residues in stromatolites, highlighting the main morphotypes and determining their composition. Discussion of the possibilities, advantages, and disadvantages of a new approach to studying biogenic ultramicrostructures in stromatolites, the reliability of the as-obtained data, and the specifics of their interpretation. Examples are provided to demonstrate the activity of which microorganisms resulted in the formation of a particular microstructure of stromatolites, forming the basis for their formal classification. The method described has been repeatedly tested by the author in the process of studying stromatolites and oncoliths of different ages; the results have been published in a number of leading journals.

   Materials and methods. Samples for analysis were collected primarily from Precambrian biogenic rocks in various regions of Russia. The study was conducted using scanning electron microscope. Specimens measuring approximately 20 × 20 mm were mechanically separated from the samples. Gold was deposited in a vacuum chamber. Organism remains in stromatolites and oncolites were identified using a TesScanMV-2300 scanning electron microscope. Their elemental composition was recorded using an EDS microanalyzer (INCA 200, Oxford Instruments), with a scan diameter of 1 μm and a polarized light scattering sensitivity of 0.001%.

   Results. Numerous fossilized remains of organisms in stromatolites are identified. Criteria for changes in their composition are established, including as a result of exposure to secondary processes. The role of the bacterial-algal community in the formation of textural and structural features of these rocks is discussed. The main morphotypes of biogenic ultramicrostructures in stromatolites are identified. The mandatory criteria for obtaining reliable data and their control by other methods are discussed. Further prospects for the study of organisms in biogenic structures are considered.

   Conclusions. The use of scanning electron microscope and the technique described by the author for the first time has made it possible to identify numerous microbial residues in stromatolites. Determination of their elemental composition and comparison of these data with the host rock facilitate monitoring the genesis of finds and obtaining useful additional information. The creation of a classification of stromatolite-forming microfossils and the analysis of the participation of organisms in the construction of textural and structural features of stromatolites will significantly expand the understanding of the formation features of these rocks and their age.

   Research subject. The contact aureole rocks of the Vostochnyi Buskun multiphase gabbroic intrusion of the Khudołaz differentiated complex (Southern Urals).

   Aim. To study geochemical interactions between the magmatic body and host volcanogenic-sedimentary rocks, to determine the physicochemical conditions of metamorphism and metasomatism, to identify mineralogical and geochemical zoning of the contact aureole, and to assess the metallogenic potential of the rocks.

   Materials and methods. Minerals were studied by optical and scanning electron microscopy; the bulk composition of rocks was determined by XRF and ICP–MS. Contact metamorphism temperatures were determined using biotite and chlorite geothermometers.

   Results. Several types of gabbroids in the Vostochnyi Buskun massif have been identified. The contact aureole of the massif is composed of three main types of rocks, corresponding to the interaction between taxitic leucogabbro and host volcanogenic-terrigenous rocks: hypersthene and clinopyroxene hornfelses in direct contact with the intrusion rocks, and chl ± ms ± bt hornfelses, forming the greater part of the exocontact. Clinopyroxene metasomatites, in comparison with more distant from the contact hornfelses, are characterized by an addition of Ca and Sr, and removal of Ti, Fe, Mg, Li, Rb, and Ba. The mineral and chemical composition of hypersthene hornfelses correspond to mafic igneous rocks and show similarities with beerbachites. Poor ore mineralization in the contact aureole rocks is represented by ilmenite, copper, and iron sulfides, including platinum-bearing pyrrhotite in chlorite-mica hornfelses.

   Conclusion. The Vostochnyi Buskun massif was formed via at least three petrogenetic phases, which resulted in the multi-stage metamorphic and metasomatic alteration of host rocks. The contact aureole formation is associated with injection of second-phase fluid-saturated taxitic olivine-hornblende leucogabbro, which were in direct contact with the host volcanogenic-sedimentary strata. The contact aureole formed in two stages: (1) a high-temperature stage (526–616 °C) accompanied by pegmatoid segregations in gabbro, hypersthene, clinopyroxene, and biotite-bearing hornfelses; and (2) a low-temperature stage (253–458 °C), which is associated with dolerite dikes and propylitic quartz-chlorite-albite veins, as well as chlorite replacing biotite. The presence of chlorine-containing apatite and amphibole indicate the participation of chlorine-bearing fluid in metasomatism, while the features of the mass transfer of ore elements indicate the absence of sulfide ore bodies under the Vostochnyi Buskun massif contact zone.

   Research subject. The material composition, formation conditions, and age of amphibolites of the Central zone of metamorphism (CZM) of the Rai-Iz massif.

   Materials and methods. Microprobe studies of minerals were conducted using a Cameca-SX100 microanalyzer; the content of petrogenic elements was determined by an X-ray multichannel spectrometer CPM-35; the REE content was determined by a mass spectrometer with inductively coupled plasma NexION 300S in the Collective Use Center “Geoanalitik”, Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences. ⁴⁰Ar/³⁹Ar dating was carried out at the Institute of Geology and Mineralogy of the Siberian Branch of the Russian Academy of Sciences according to A.V. Travin’s method. Results. The petrography and geochemistry of the amphibolites of the CZM Rai-Iz massif were studied; the parameters of their metamorphism were established, and the age of ⁴⁰Ar/³⁹Ar was determined. Two types of amphibolites were identified: garnet amphibolites, epidote-garnet amphibolites, and clinopyroxene-amphibole and amphibole-phlogopite-garnet rocks. The main minerals were found to be amphibole and garnet. Amphibole corresponds to edenite, pargasite, and ferropargasite. In some amphibole samples, chemical zonation was established, manifested in the depletion of the marginal parts of Al₂O₃ and FeO grains relative to the central ones, while the MgO content increased from the center to the edge. Garnets from garnet and epidote-garnet amphibolites exhibited an almandine-grossular composition with pyrope (3–16 %) and spessartine (3–13 %) components; in amphibole-phlogopite-garnet rocks, garnet demonstrated an almandine–pyrope composition. In the pomegranate, the following chemical zonation was established: the FeO content increases from the center to the edge of the grains, while the MnO content decreases. The age of amphibolites determined by the ⁴⁰Ar/³⁹Ar method (405.2 ± 5.4 Ma) corresponds to the Lower Devonian. The averaged formation parameters of amphibole-bearing rocks correspond to P = 6–13 kbar, T = 430–860° C, and to the boundary of amphibolite and greenschist facies and the boundary of amphibolite and granulite facies. REE spectra in the studied rocks, normalized relative to chondrite, showed the predominance of heavy lanthanides over light ones. The character of REE distribution is close to N-MORB basalts.

   Conclusion. The studied rocks formed at the boundary of the early and middle Devonian. Their formation was associated with regional metamorphism in the conditions of the onset of collision.

   Research subject. Volcanogenic rocks belonging to the Sablegorskaya formation of the Upper Riphean–Vendian in the southern part of the Lyapin tectonic zone (Northern Urals).

   Aim. Reconstruction of the stages and paleo-environments of volcanic rock formation.

   Methods and materials. Geochemical studies and interpretation of geochemical parameters were performed using geological and isotope-geochronological data.

   Results. Geochemical features of volcanogenic rocks belonging to the Sablegorskaya formation indicate heterogeneity of their compositions, which may indicate the presence of several rock groups formed under different conditions. Radiological determinations of the age of rocks have a range of more than 100 million years, from the Ediacaran to the Late Cambrian (Furongian). This finding does not contradict the idea of the action of several pulses of magmatic activity. An assumption can be made about a spatial combination of volcanogenic formations of several paleoenvironments of different ages – Precambrian suprasubduction and Early Paleozoic rifting – within the Lyapin tectonic zone.

   Conclusions. An assumption is made that the volcanogenic rocks currently attributed to the RF₃-V Sablegorskaya formation were formed in the rear of the Late Precambrian active continental margin at an early stage of continental rifting in the Early Paleozoic.

   Research subject. Metavolcanics of the Sablegorskaya Formation collected in the area of Mount Redka on the western slope of the Northern Urals (Komi Republic).

   Aim. To study the petrogeochemical composition of metavolcanics and mineral forms of Nb and rare-earth elements contained therein.

   Materials and methods. Rock samples were collected from eluvial-deluvial rubble and mine workings on the southeastern slope of Mount Redka. The analytical procedures included determination of the contents of rock-forming oxides in rocks by the classical chemical method; measurement of concentrations of rare, trace, and rare-earth elements by inductively coupled plasma mass spectrometry (ICP–MS); microprobe analysis of mineral composition.

   Results. The studied metavolcanics of the Sablegorskaya Formation belong to rhyolites and trachyrhyolites of normal and subalkaline series formed in an intraplate setting. The presence of rare-metal (Nb-rutile) and rare-earth (allanite, monazite, xenotime, nioboeschinite-Y) in the mineral composition of the rocks was established. They form a scattered dissemination of grains 20–50 μm (Aesh(Y), Xnt, Mnz) and 50–500 μm (Nb-Rt, Aln) in size. We consider their appearance to be a result of magma crystallization, autometasomatic processes, and subsequent metamorphism.

   Conclusions. The presence of rare metal and rare-earth minerals in the composition of acid metavolcanics of the Sablegorskaya Formation of the Northern Urals was established. An assumption is made about the possibility of mobilization of Th, U, Y, Nb, and REE from rhyolites and trachyrhyolites in tectonically active zones with the formation of corresponding ore occurrences.

   Research subject. Zincochromite in veins of chromium-bearing mica (fuchsite) in metarhyolites.

   Aim. To establish the relationships of zincochromite with other minerals and Au–Pd mineralization. To determine the place and role of zincochromite in the process of mineral formation.

   Methods. Polished sections from ore samples and concentrates of heavy minerals mounted in epoxy resin were studied using optical and electron microscopes. The composition of minerals was determined using SEM/EDS.

   Results. Idiomorphic crystals of zincochromite in fuchsite veins (up to 12 µm in size) are localized directly in fuchsite, less frequently in allanite; intergrowths with native gold and palladium arsenoantimonides were noted. Zincochromite contains 15.5–27.5 wt % ZnO and 40.2–47.5 wt % Cr₂O₃. The most Zn-rich mineral has the following formula: (Zn_0.77Fe²⁺_0.13Mn_0.10) (Cr_1.37Fe³⁺ _0.42Al_0.21)₂O₄. The Cr₂O₃ content in fuchsite veins varies across a significant range (from 0.2 to 12.4 wt %); however, zincochromite is usually enclosed in fuchsite with a Cr₂O₃ content of more than 1.5 wt %.

   Conclusions. All rocks in the area of the Chudnoe deposit, including ores, are metamorphosed in the conditions of biotite subfacies of greenschist facies. The formation of zincochromite is associated with metamorphic transformations of fuchsite veins enclosed in rhyolites. During recrystallization of fuchsite, zincochromite crystals are formed at the expense of the latter. Zinc required for the synthesis of zincochromite came from metamorphosed fuchsite veins and host rhyolites.

   Research subject. In 2019, the city of Tulun in the Irkutsk Oblast experienced devastating floods, causing significant damage to infrastructure and the population. Detailed analysis and monitoring are required.

   Aim. Development and testing of a methodology for integrating data from Sentinel-1 and 2 satellites for effective flood monitoring, analysis of their dynamics, and assessment of suitability for identifying flooded areas.

   Materials and methods. Images from Sentinel-1 radar satellites and Sentinel-2 optical satellites were used. Data processing was carried out using SNAP and Global Mapper, including geometric correction, filtering, and data integration. Emphasis was placed on temporal synchronization, spatial resolution unification, and weighted summation methods.

   Results. The study revealed significant changes in the dynamics of the water surface area from 2017 to 2024, especially in 2019. The flooded area ranged from 3.252 to 12.018 km², with an average value of 4.645 km². Data integration significantly enhanced monitoring accuracy.

   Conclusions. The integration of Sentinel-1 and Sentinel-2 data improved the accuracy of flood scale assessments, highlighting the importance of a comprehensive approach. The results can be used to improve risk management strategies and develop damage reduction measures, as well as to provide more complete and reliable information for decision-making.

   Research object. The epicentral zone of the destructive Chuya earthquake of 2003 (M = 7.2), characterized by a prolonged nonlinear aftershock period. The epicenter of the earthquake was located in the intermountain pass between the Chuya and Kurai depressions of the Altai Mountains, only 15 km from the study site located in the western part of the Chuya depression in the Chagan River valley.

   Aim. To determine the geoelectrical structure of the Chagan River valley, to identify areas of development of permafrost deposits. Additionally, to track the dynamics of changes in the geoelectrical parameters of permafrost deposits during the aftershock period of the earthquake based on regular long-term observations, and to compare the geoelectrical data with the seismicity characteristics of the Chuya–Kurai seismic active zone.

   Methods. Electromagnetic methods with a controlled source were used to study the distribution of permafrost deposits in the valley, which exhibited uneven distribution.

   Results. The study allowed us to determine variations in the thickness and specific electrical resistivity of the layers of permafrost. Comparison of the seismic activity parameters of the area with the geo-electrical characteristics of the permafrost showed a significant influence of changes in seismic regime on these properties. During the periods of activation, permafrost degraded, while recovery occurred during the periods of reduced activity, with variations in geo-electrical parameters reaching 50–80 %.

   Conclusions. The obtained results demonstrate the potential of using electromagnetic methods for continuous monitoring of the state of permafrost, emphasizing their effectiveness in understanding the relationship between seismic activity and the state of permafrost.