Research subject. The author investigates sections of the Vendian stratigraphy in the West Bashkirian subzone, written for an Explanatory Note to sheet N-40 – Ufa of the State Geological Map 1000/3 of the Russian Federation, as well as the results obtained with various thematic (stratigraphic, paleontological, lithogeochemical, paleomagnetic, etc.) studies of the
Vendian sedimentary sequences of the indicated subzone of the Bashkirian meganticlinorium.

   Materials and methods. A comparison and analysis of research materials was conducted. The research materials included facts, ideas and arguments in favor of certain conclusions and ideas of various authors.

   Results. A suggestion was made that studies into the architecture of the Vendian deposits of the Southern Urals, apparently, had almost reached perfection. At the same time, the affiliation of different formations to the regional stages of the Vendian of the East European Platform is still interpreted differently. Studies into the Vendian macro- and microfauna on the western slope of the Southern Urals can only be considered at their nascent stage. The dating of detrital zircons from sandstones of the Asha Group should undoubtedly be continued. For the Vendian of the western slope of the Southern Urals, the first steps have been taken regarding the dating of zircons from volcanic tuffs/ashes. These works are still far from being completed. The peak of paleomagnetic studies into the sedimentary sequences of the Vendian, to a certain extent, may have been passed; nevertheless, these research works should also be continued. Finally, only preliminary steps were taken more than 20 years ago in the study of the chemical composition of heavy minerals, which made it possible to obtain fundamentally new information on the composition and evolution of the sources of clastic material for the sedimentary sequences of the Asha Group. Works of this kind also needs to be continued.

   Conclusion. The conducted analysis of the studies into the Vendian sedimentary sequences of the Southern Urals published in the first two decades of the 21st century made it possible to identify their strengths and weaknesses, as well as to outline directions for further work.

   Research subject. Late Givetian-Early Frasnian brachiopods, conodonts and spores of higher plants from the Timan Horizon of borehole No. 8 Tsarichankaya.

   Material and methods. The biostratigraphical me thod was used to isolate fossils and to determine the taxonomic compositions of brachiopods, conodonts and higher plant spores from deposits drilled by borehole No. 8 Tsarichanskaya (interval 3637.00–3647.00 m), to substantiate their age and carry out a correlation. An improved technique of I. Kh. Shumilov and O. P. Telʼnova was used when proces sing spore samples.

   Results. The uppermost Givetian zonal species Skeletognathus norrisi (Uyeno) was identified. Brachiopods and higher plant spores in association with conodonts are typical for the Upper Timan Subhorizon. The results obtained clarify the paleontological characteristics of the Givetian–Frasnian boundary interval on the Russian platform. The findings indicate a wider range of the Skeletognathus norrisi stratigraphical distribution (the latest Givetian–Early Frasnian), including the Upper Timan Subhorizon.

   Conclusions. The marine and terrestrial fossils isolated from the same rock samples allowed the authors to provide a complex paleontological characteristic of the Upper Тiman Subhorizon, which is considered as being a variant of the D2-D3 boundary. It is significant for interregional correlations of different facies deposits.

   Research subject. Fe- and Al-rich metapelites of the Teya, Garevka and Angara complexes of the North Yenisei Ridge (western margin of the Siberian craton) were studied.

   Research methods. Recently-obtained geochronologic (SHRIMP II U-Pb zircon dating) and geochemical data on the distribution of major and trace elements were used to reproduce the composition and age of the protolith, along with the paleofacies formation conditions.

   Results. The ferruginous-aluminous metapelites of the North Yenisei Ridge consitute redeposited and metamorphosed products of Precambrian weathering crusts predominantly of the kaolinite rather than lateritic type, as was previously thought. The chemical weathering of rocks in the Early Proterozoic on the Yenisei Ridge did not reach the deep stage of lateritization with the formation of zones of final decomposition of aluminosilicates; however, this process was limited to the formation of weathering products of predominantly kaolinite-illite-montmorillonite-quartz composition.

   Conclusions. The petro- and geochemical characteristics of the studied metapelites are mainly due to the features of sedimentation during the formation of the protolith, which could have been formed due to the erosion of the Lower Proterozoic microgneisses of the Siberian craton with ages in the range of 1962-2043 Ma with the involvement of granitoid and volcanic admixture of mafic rocks into the erosion area and subsequent accumulation in marginal continental shallow basins under the conditions of a humid climate and a calm tectonic regime. These results are consistent with the data of lithofacies analysis and geodynamic reconstructions of the Precambrian evolution of geological complexes in the North Yenisei Ridge.

   The article presents an overview of the main stages of magmatism and ore mineralization of copper and other metals of the Tekturmas ophiolite belt and related structures of Central Kazakhstan. The age, composition and probable tectonic settings during the formation of Cu-Ni deposits in Central Kazakhstan associated with sulfide mineralization are discussed. The Tekturmas ophiolite belt includes formations of three lithological types: basaltic Karamurun and Kuzek formations, siliceous Tekturmas and Bazarbai formations and clastic Sarytau, Airtau and Yermek formations. The potential ore mineralization of the Tekturmas ophiolite belt is associated with plutonic mafic and ultramafic rocks of the ophiolite section, within the Karamurun and Kuzek formations of the Tekturmas and Bazarbai segments, respectively. The Uspenka rift zone, which is adjacent to the Tekturmas ophiolite belt, includes three volcanogenic-sedimentary associations of Early-Middle Silurian, Early-Middle Devonian and Late Devonian-Early Carboniferous ages. The Uspenska copper deposit is related to the youngest Late Devonian-Early Carboniferous association. The geological structure of the territory, which includes magmatic bodies with Cu-Ni ore mineralization, should serve as a basis for an integrated approach to studying oreforming systems. The most promising locations of copper mineralization within the Tekturmas ophiolite belt and Uspenska rift zone are the Kamkor and Uspenska-Bella deposits and the Urtynjal, Ordobasy and Shopa ore occurrences. All these deposits are associated with mafic and ultramafic intrusive complexes. The main regional and local geological characteristics of these deposits and ore occurrences, along with the types of ore mineralization, are discussed. It is argued that Central Kazakhstan has limited prospects for the discovery of large Cu deposits; however, the discovery of medium-size and small-size deposits of that type is quite possible. The discovery of new large Cu-porphyry deposit in the Tekturmas ophiolite belt is also unlikely; however, additional prospecting works aimed at identification of new ore bodies in the vicinity of already known deposits and ore occurrences presents research interest.

   Research subject. For the first time, the results of a study of hydrothermal-bacterial carbonate structures and a shell bank of brachiopods on the surface of the effusive sequence of the Late Triassic Tessel paleovolcano are presented.

   Methods. Petrographic thin sections were studied using an Olympus BX 5 microscope with an Olympus DP 12 camera. Geochemical investigations were performed according to the conventional methodology by an inductively coupled plasma mass spectrometer (ICP-MS). The isotopic composition of carbon was determined by isotope ratio mass spectrometry (IRMS) by a Deltaplus Advantage instrument. The mass spectrometer was paired with an EA Flash1112 analyzer and a TC/EA convector. When measuring, the NBS-19, NBS-18, and IAEA-C-3 standards were used.

   Results. The data obtained on the geology, geochemistry, and isotopic composition of the studied materials confirm the existence of a symbiosis between brachiopods and protozoa. The primary formation of organic matter and carbonate of bacterial structures occurred due to the processing of paleofluids by the community of bacteria and archaea. These organisms created carbonate, sulfide and organic matter in a suboxide environment of hydrogen sulfide and methane. The biocenosis of the shell bank of brachiopods was characterized by a poor taxonomic composition and a high biological productivity. The formation of a shell bank of brachiopods with bacterial carbonate edifices took place during the period of volcanic activity and continued during breaks in eruptions. The results of geochemistry and the carbon isotopic composition of the carbonate of bacterial buildups confirm the deep nature of the paleofluids. The Norian age of paleovolcanism was determined from finds on the surface of the terrigenous- volcanic sequence of brachiopods Worobiella ex gr. caucasica Dagys and ammonite Megaphyllites insectus (Mojsisovics).
   Conclusions. According to geological features, the material of the shell bank of brachiopods with bacterial carbonate structures on the surface of the Tessel paleovolcano belongs to the ancient hydrocarbon seeps-carbonate. Based on their genesis and formation material, these formations should be referred to as Triassic methanoliths. Signs of allocation of similar formations in other time intervals and regions are given. Emissions of fluids with hydrogen sulfide and methane by the Tessel paleovolcano in the Late Triassic may have been related to the causes of the “global extinction”.

   Research subject. The estimations of oil resources in Western Siberia obtained using a basin modeling of the Bazhenov formation as an oil source stratum indicated a significant deficit of its potential, calculated based on the pyrolytic kinetic parameters of catagenesis.

   Aim. To search for possible additional oil generating mechanisms parallel to catagenesis, thus clarifying the conceptual foundations of the modern theory of the organic origin of oil.

   Key points. Based on a review of literature publications, a hypothesis was formulated about the evolution of organic matter from sedimentary flow floccules to the injection of proto-oil into the microcracks of the autofluid fracturing of source rocks. In the upper unconsolidated bottom sediment layers, biofilms appear whose microbial matrix forms a basis for future kerogen. Proto-oil bitumoids appear as a by-product of biofilm microbial metabolism under the anaerobic conditions at diagenesis stage. Рroto-oil bitumoids are encapsulated and absorbed on the surfaces and inside the chambers and conducting channels of the biofilm polymer matrix (future kerogen). Local ultra-high pressure (LUHP) inside kerogen grains appears at the final “smectite – illite” transition stage of host clays, acting as a driving force for encapsulated bitumoid expulsion from kerogen grains. On the walls of microcracks, proto-oil bitumoids undergo hydropyrolysis, consuming cohesive film water and changing the surface philicity. Microphotographs and SEM images of thin sections are provided in order to illustrate LUHP-expulsion traces. Two types of oil source rocks are differentiated based on the possibility of proto-oil LUHP expulsion: those with a plastic mineral framework and a rigid mineral framework.

   Conclusion. The presence of porous spaces filled with bitumoids was established in the kerogen of immature potentially oil source rocks. This mass of encapsulated bitumoids is an additional resource of oil generation within the “oil window”. Their expulsion volume can be estimated and attributed to a certain temperature range. Directions for further research are outlined.

   Research subject. Chromite ores and massive chromitites with alumina (low chromium) chrome spinelide (the Podennoye deposit deposit) and chromite ores with high-chromium chrome spinelide (Kurmanovskoye deposit) of the Alapaevsky hyperbasite massif.

   Materials and methods. Samples of chromite ores and massive chromitites collected during field research were studied in transparent sections using chemical analysis and electrical methods (electrical conductivity, dielectric losses).

   Results. The temperature dependences of electrical resistance and dielectric losses in the temperature range of 20‒800°C were obtained. The electrical parameters lgRₒ and Eₒ were determined, and the inverse linear relationship bet-ween them was revealed. The electrical parameters for the three groups of samples were found to differ depending on the degree of metamorphic changes. It was established that an increase in metamorphism leads to an increase in lgRₒ and a decrease in Eₒ. For the studied samples of chromite ore from the Podennoye deposit, Eₒ and lgRₒ vary from 0.61 to 0.96 and from 2.5 to –0.41, respectively. In the Kurmanovskoye field, these parameters vary from 0.81 to 1.35 and from 0.95 to –2.8, respectively. For the studied samples of chromitites from the Podennoye deposit, Eₒ varies from 0.21 to 0.41, while lgRₒ varies from –0.08 to 1.67. In this case, the coefficients a and b are different for each group of samples. For some samples, the chemical composition was determined, and for six samples (two samples from each group), the content of ferrous and trivalent iron oxides in the original sample and a duplicate sample after calcination at temperature of up to 800 °C was determined. Relative change in the ratio of ferrous and trivalent iron oxides in the initial sample (FeO/Fe₂O₃)* and a duplicate sample (FeO/Fe₂O₃)** H = [(FeO/Fe₂O₃)*/(FeO/Fe₂O₃)**] was compared with the position of the maximum of dielectric losses on the temperature scale. In the coordinates H–T, °C, the studied samples, depending on the metamorphic changes, occupy a certain place.

   Conclusions. The study indicates the potential of the obtained information to be used as petrogenetic indicators of chromite deposits with a simultaneous assessment of the degree of metamorphic changes.

   Research subject. The Ilych-Chikshinskaya fault system involved in the structure of the Izhma-Pechora monocline. The Ilych-Chikshinskii deep fault is the southern branch of the Pripechorskaya fault system, which separates the Timansky and Pechoromorsko-Bolshezemelsky geoblocks.

   Materials and methods. The data obtained during profile detailed magneto-metric and radon surveys, the materials of fund seismic surveys, and the maps of gravitational and magnetic fields of various scales were used. Measurements of the volume radon activity were carried out using portable radiometers РРА-01М-01 and Alfarad plus. Magnetometric observations were carried out with a MINIMAG magnetometer.

   Results. Radon surveys on two profiles were conducted in different years. According to the obtained results, the faults of the Ilych-Chikshin skaya system have no obvious manifestation in the radon field. The volume radon activity in different periods varied across a wide range from 50–200 to 200–600 Bq/m3, which indicates the absence of a constant deep source of radon. According to the data of detailed magnetometric surveys, the Ilych-Chikshinskii fault, against the background of a calm negative field, corresponds to a gradient zone of 4 km wide.

   Conclusion. The presence of low-intensity discontinuous radon anomalies along the line of profiles is associated with increased concentrations of parent uranium radionuclides in the soil and near-surface rocks. Since the rocks of the basement and sedimentary cover are nonmagnetic, the local magnetic anomaly indicates the presence of mafic and ultramafic intrusions in the zone of the Ilych-Chikshinskii fault.