Research subject. Volcanogenic formations of the Navysh complex of the Ai Formation in the Taratash anticlinorium of the Southern Urals, which have been thought to be Lower Riphean. Results. The U-Pb dating of zircons from metabasalts of the Navysh complex were obtained, reflecting specific characteristics of their age. The isotope parameters of zircons of the К2247 sample divide them into two groups. The first group unites the ancient crystals aged Т₁ = 2943 ± 31 and Т₂ = 2713 ± 49 Ma, while crystals in the second group belongs to a much age - Т₃ = 451.6 ± 9.1 and Т₄ = 366.4 ± 6.0 Ma. No Riphean crystals were found in sample К2247. Conclusions. The dates obtained for the supposed Riphean complexes have shown that the Paleozoic magmatism took place not only in the eastern slope of the Urals, but also in the western slope. This process occurred several times.

Research subject. Sections of the Upper Vendian-Lower Cambrian, opened at the beginning of the XXI century by wells Avloga-12R, Utkina Zavod - 1 and Thais-2 with a depth of 150-370 m, in the north and in the central part of the Leningrad region. Methods. The analysis of the structural and textural features of the rocks of the contact layers, the distribution of allotigenic (quartz, feldspar) and autigenic (pyrite, siderite, glauconite) minerals in them allowed us to supplement the characteristics of the Old Russian, Vasileostrovsky and Siverskaya formations previously isolated in these wells. The use of the structural-genetic method made it possible to clarify the volumes and boundaries of the formations, to prove the absence in the section of the Lomonosov formation, previously isolated in the well Thais-2. Results. Based on the reconstruction of sedimentation conditions and settings, the development of sedimentation processes over time, three transgressive-regressive sequences of layers - cyclothemes were established in sections. The first corresponds to the Old Russian, the second - Vasileostrovskaya, and the third - Siverskaya formation. It is shown that in the studied part of the paleobasin at the end of the Vendian-the beginning of the Cambrian, there were open shelf environments (an area of mobile shallow water with underwater shafts (zone Y), an area of relative deep water with background and storm sedimentation (zone X) and a transitional zone of patchwork sands between X and Y with a variable hydrodynamic regime. The maxima of transgressions corresponding to the development of the deepest water environments occurred in the middle of the Old Russian, Vasileostrovsky and Siversky time, and the maxima of regressions marked by shallow water deposits belong to the end of these time intervals. According to isochronous levels - maxima of transgressions and regressions, correlation of well sections was performed.

Research subject. Limestones of 11 sections of the Mid-Carboniferous boundary interval in the Southern and Middle Urals were studied. Sections of the western slope of the Urals (2 sections) refer to the East European platform, while the eastern Urals carbonate strata (9 sections) are fragments of the carbonate platform formed in the residual basin of the Ural Ocean. Material and methods. The lithological features of limestones of all considered sections were identified, the distribution and main characteristics of 28 trace (rare and scattered) elements, as well as Al and Fe, were studied and analyzed. Results and conclusions. The main characteristics of sedimentary basins, including the redox state, terrigenous material provenances, climatic conditions and the influence of endogenous processes, primarily volcanism, were clarified and evaluated. The results confirm the point of view about the short-duration hiatus at the Mid-Carboniferous boundary and the absence of a catastrophic drop in the World Ocean level. There are also no evidences of a significant cooling period. Geochemical and lithological data indicate local unconformities, transformations of sedimentary environments and sources of siliciclastic admixtures, as well as some climate humidization at the Mississippian-Pennsylvanian boundary.

Research subject. Fluid inclusions in quartz of three vein systems associated with tectonic cracks occurred during the development of thrust and shear deformations of the Western Transbaikalia. Vein systems localized in volcanic, terrigenous and granite rocks. Methods. The composition of fluid inclusions was studied by microthermometry, Raman spectroscopy and gas chromatography-mass spectrometry. Results. The quartz under study was formed by high-density medium-temperature NaCl-KCl and a low- and medium-salinity water-carbon dioxide fluid (2-5 wt % NaCl eq.). A distinctive feature of quartz of different vein systems was found to be the gas phase composition of inclusions associated with the composition of host rocks. The minimum temperatures of vein quartz formation were determined to range from 180 to 450°C under the minimum fluid pressure values of 0.7-2.9 kbar. Conclusions. Complex vein systems of the junction zone of the Baikal-Muiskaya and Barguzino-Vitimskay SFZ, confined to different host rocks and having different structural positions, are characterized by a similar fluid composition and a common thermodynamic history reflecting the change of deformation aggregates. The metamorphogenic-hydrothermal nature of the fluid involved in the formation of quartz vein systems was established. The development of the hydrothermal system was accompanied by its influence on the host rocks, which was manifested in the variations of fluid composition. The evolution of a single hydrothermal system is associated with tectonic deformation processes, which can be described by three dynamic stages corresponding to three quartz generations.

Research subject. Multidisciplinary characteristics of the Siphonodella belkai Dzik conodonts, which an index species in the Tournaisian (Mississippian) conodont zonation. Materials and methods. Data on conodonts collected from the North Cis-Urals and Subpolar Urals sections was used. In total, 89 specimens of Siphonodella belkai were found in the Kozhim Eiver basin sections (Subpolar Urals) and the Vangyr River section (Tchernyshev Uplift). The histology, morphology and ontogeny of platform elements of this species were studied using SEM, optic microscope and X-ray micro-CT. In total, 45 complete specimens were biometrically studied. Results. Siphonodella belkai can be reliably distinguished by having a smooth lens-like platform and bearing developed rostral ridges. The paralamellar tissue occurs in the platform and rostral ridges; distribution of the albid tissue is restricted by carina denticles in the cusp neighborhood. Sinistral and dextral P1 elements of the species compose asymmetric pairs and differ by the position and number of rostral ridges (Class III of symmetry). The element outline remains constant in ontogeny. Rostral ridges appear at early ontogeny stages, when an element is of 0.4-0.5 mm in length, thus allowing reliable taxonomic diagnostics. Conclusions. Siphonodella belkai is known from the moderately deep-water deposits of the Central and Eastern Europe and South China. The base of the S. belkai zone, marked by the first appearance of the eponimic taxon, coincides with the base of the Upper duplicata zone. Distinguishing the S. belkai zone as a standard zone seems unreasonable due to the rarity, restricted area and specific ecology of S. belkai. This zone is of low correlation potential.

Research subject. Boundary Jurassic-Cretaceous sediments of the western part of the Yenisei-Khatanga Regional Trough. Materials and methods. The main correlation tools were seismostratigraphic, logging, and biostratigraphic methods. Litho- and biofacies methods were used to reconstruct the development conditions of the Yanovstan Formation and the NKh group of the Ryazanian Stage reservoirs. Results. The composition of macro- and microfauna complexes was defined, analogues of the ammonite and foraminiferal zones of the Upper Volgian substage and the Ryazanian stage of Siberia were established. The structure of the Upper Jurassic and Ryazanian complexes of the western part of the Yenisei-Khatanga Regional Trough was detailed. Conclusions were made about the formation conditions of the Volgian and Ryazanian deposits. Conclusions. The sediments were found to have been formed in a sea basin with stable salinity and low water energy, in relatively deep-water conditions. Mixed turbidite systems with multipoint supply sources were identified, in which the terrigenous material was supplied from southeast to northwest.

Research subject. Framboidal pyrites and sulfide micro-concretions in carbonaceous-siliceous and ore rocks of the Safyanovskoye deposit (Middle Urals). Aim. To identify the signs of vital activity of microbial communities in bottomhydrothermal deposits using the example of the Safyanovskoye sulfide deposit. The methods. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Results. TThe analyzed ore and carbonaceous-siliceous rock samples showed the presence of mineralized silicon dioxide films covering framboidal pyrites. Micro-concretions were found to consist of microfossils of filamentous organisms and framboids. Pyrite samples included the remains of tubular casts of sulfidized vestimentifera and polychaetes, associated with framboids. The possibility of using fossilized remains of microbial communities for distinguishing bottom-hydrothermal facies among pyrite deposits was confirmed. Conclusions. Hydrothermal-sedimentary deposits are characterized by the traces of specific microbial communities, since prokaryotic organisms were pioneers in hydrothermal oases. Their long active existence created a basis for the second trophic link, i.e. filter feeding macrofauna and endosymbiotrophs. These organisms, in turn, formed another level in the food chain of the trophic pyramid. It is believed that micro-concretions and framboidal pyrites are indicators of the vital activity of microbial communities.

Research subject. The geological structure, petro-geochem ical features of the ore-bearing rocks of the Voznesenskoe gold ore deposit (Southern Urals) and the geodynamic conditions of its formation. Methods. The content of petrogenic oxides was determined using silicate analysis; rare elements were determ ined using ICP-MS methods by an EIAH 9000 mass spectrometer and ICP-AES by an ICPE-9000 mass spectrometer. Results. The Voznesenskoe deposit is confined to a fragment of the crustal part of the section of harzburgite-type island-arc ophiolites. The ophiolite section is composed of taxite gabbroids, a sequence of dolerites, basalts, basaltic andesites and their tuffs, in places separated from gabbroids by lenses of serpentinites, and a package of subparallel dikes of porphyry gabbro-dolerites, gabbro-diorites, and diorites. Volcanics and dyke rocks with normal alkalinity and tholeiitic composition exhibit the geochemical characteristics of suprasubduction formations. In terms of chemical composition, they are comparable to the volcanic rocks of the pyritebearing complexes of the Baimak-Buribaevskaya Formation (D₁e₂). At the same time, the Voznesensky rocks have a number of distinct features, which are likely to be related to the geodynamic setting of their formation. In particular, ore-bearing effusive rocks and dykes differ from volcanic rocks of pyrite-bearing complexes in terms of a higher titanium content, the absence of boninite and silicic volcanic rocks, as well as the predominance of porphyry rock types. Conclusion. The conducted analysis of geochemical data using the V-Ti/1000 and La_N/Sm_N-TiO₂ diagrams suggests that the association of mafic volcanic rocks and ore-bearing dykes of gabbro-dolerites, gabbro-diorites and diorites of the Voznesensky deposit was formed in the back-arc basin of the Late Ems frontal island arc.