Research subject. Problematic issues of general stratigraphy are considered, including the Karpinsky principle, the unification of autonomous zonal biochronological scales (BCS), the basics of stratigraphic classification, the relation of zonal biostratigraphic and chronostratigraphic units. Materials and methods. The existing standard solutions to the above issues are analyzed. An attempt is made to reveal the logical sources of contradictions and to pave ways for a consistent synthesis. Results. The necessity for a successful solution of these issues to abandon the identification of the biochronological scale and the geological section is shown. From the recognition of the zone as the smallest subdivision of the biochronological scale, the linearity of the zonal subdivisions of the scale follows, which makes it a correct tool for performing basic stratigraphic operations – section subdivision and correlation of the boundaries of stratigraphic units. Strict differentiation of the scale from a section studied using this scale makes it possible to fulfill all the requirements of the Karpinsky principle regarding dividing horizons with mixed fauna. The same condition underlies the creation of a stratigraphic classification, which must be preceded by a clear separation of the material (“mapped”) stratigraphic units of the Earth’s crust and units of chronological scales, which are used for their correlation. Placing them in a single “dualistic” stratigraphic classification cannot give a satisfactory result. The creation of autonomous zonal scales should be preceded by the definition of the biozones of the species used to build these scales, according to the normative (standard) zonal scale for a given stratigraphic interval. Taking into account the minimum dimension of the zonal subdivisions of the standard scale, the zones of autonomous scales distinguished by this method correspond to a whole number of normative zones, and, therefore, the boundaries of the stratozones established on the autonomous scales, in this case, will certainly coincide with any boundaries of the stratozones, distinguished on the normative scale. This procedure makes it possible to perform the unification of autonomous zonal BCSs based on different groups of fossils. Zonal BCS performs correlation functions, zonal units are a tool for chronological identification of remote geological objects, including the boundaries of chronostratigraphic units, although not being included in their hierarchy. Conclusions. A biochronological scale is a model of the biochronological calculation of geological time and cannot be identical to what it models. Differentiation of the scale from a section studied using this scale is an indispensable condition that precedes and ensures the successful solution of long-living problems of general stratigraphy.

Research subject. Pragian conodonts from the Mindigulovo section on the western slope of the South Urals. Aim. Conodont-based biostratigraphy of the Pragian deposits. Materials and methods. This study is based on the biostratigraphic method: identification of conodonts using conventional techniques, recognition of Pragian conodont associations, zonal scale proposal and correlation. Results. The Pragian beds in the Mindigulovo Section in the latitudinal flow of the Belaya River are characterized using conodonts for the first time. The following conodont-based subdivisions at the rank of beds with fauna are recognized (from bottom to top): Beds with Gondwania irregularis, Latericriodus steinachensis, Beds with Pelekysgnathus serratus, Beds with Gondwania profunda, Pseudogondwania kindlei and Beds with Polygnathus cf. pireneae. Conclusions. The recognized conodont-based units can be directly correlated with the standard zonal scale of the Pragian. The conodont assemblage studied contains taxa characterizing the Gondwania irregularis–Gondwania profunda, Pseudogondwania kindlei–Eognathodus zeravshanicus, Polygnathus pireneae lineage, also known in the Pragian successions of Australia and the South Tien Shan. The co-occurrence of the deep-water family Eognathodidae and the shallow-water Icriodontidae in the Mindigulovo Section enables the correlation of different facies sections.

Research subject. Spores of higher plants from the Early Frasnian deposits of the Main Devonian Field. Material and methods. The work is based on the biostratigraphic method with the following stages: determination of the taxonomic composition of palynospectra, substantiation of the host rocks age, and data correlation. Palynological analysis was conducted using an improved technique by I.Kh. Shumilov and O.P. Telnova, which produced positive results. Results. For the first time, spores of higher plants were found in the sections of the Amatsky and Plavinsky Horizons of the Main Devonian Field. The palynospectra of the Podsnetogorsk layers of the Amat and Snetogorsk layers of the Plyavinsky Horizons were described. The palynospectra of the Podsnetogorsk layers are correlated with the palynoassemblage from the upper part of the Timan, and the Snetogorsk layers are correlated with the palynoassembly of the Sargaev Horizons, established in the Timan-Pechora province. The identified palynospectra complement the associations of vertebrate and invertebrate fauna, as well as rare macroflora, previously studied in these sections. The palynospectra from the Snetogorsk beds are correlated with the palynoassemblage of the Cristatisporites deliquescens – Archaeoperisaccus mennerii regional zone of the Timan-Pechora province. The palynozone characterizes the stratigraphic interval corresponding to the rugosa–transitans conodont zones (middle–upper part of the Sargaev Horizon). Conclusions. The established palynoassemblage from the Snetogorsk layers corresponds to the middle part of the Sargaev Horizon – the stratigraphic interval of the rugosa conodont zone. For the first time, the conducted palynological studies established a binding between the regional stratigraphic unit of the Main Devonian Field and the standard conodont zone.

Research subject. The Dodo and Puiva quartz crystal deposits in the Neroiskiy mineral province (Subpolar Urals) were studied. Although these deposits have received sufficient research attention, a number of issues remain to be elucidated, including the age of crystal-bearing mineralization and the age of host rocks. Aim. In this work, we aim to determine the age of the metasomatites that bear quartz crystal mineralization and to develop a model of the formation of the Dodo and Puiva deposits. Materials and Methods. ⁴⁰Ar/³⁹Ar dating was carried out according to the method described by A.V. Travin et al. The argon isotope composition was measured on a Micromass 5400 mass spectrometer (IGM SB RAS). Results. Microprobe studies of the mineralogy of the Dodo and Puiva quartz crystal deposits were carried out. The temperatures of meta-somtaite formation were determined to range within 339–364°C. Six main structural and morphological types of quartz veins were identified and described. The ⁴⁰Ar/³⁹Ar ages of mica of quartz crystal deposits and host metamorphic schists were determined. Reliable plateaus were obtained, the values of which ranged within 251–257 Ma and agreed with each other within the deviation (average for 4 dates is 255 ± 2 Ma). Conclusion. A new model for the formation of quartz crystal deposits in the Subpolar Urals is proposed. The obtained ⁴⁰Ar/³⁹Ar ages correspond to the period of the post-orogenic extension of the Urals. At that time, a system of meridional grabens and rifts was formed in the Urals and in the West Siberian Plate. At the same time, and as a result of the same stretching impulse, large blocks of the middle crust (granite, schist, etc.) were brought to the Earth’s surface in the Urals. During the rise of deep blocks, at a depth of 10 km, a sharp, approximately 3-fold drop in fluid pressures (from lithostatic to hydrostatic) and a strong decrease in temperatures due to adiabatic expansion and the throttling effect occurred. The obtained ⁴⁰Ar/³⁹Ar ages (255 Ma) reflect not only the age of the quartz crystal deposits of the Subpolar Urals, but also place the moment of rise of the entire Central Ural uplift above a depth of 10 km, i.e., to the level of the upper cortex.

Research subject. The Zhaman-Koitass granite-leucogranite massif of the Borovsk complex in Northern Kazakhstan. In the platform cover of the West Siberian plate, overlying granite-leucogranites, a large uranium deposit Semizbai of sandstone type is localized. Materials and methods. Geochemical, mineralogical, and geochronological studies of granite-leucogranites were conducted by X-ray fluorescence analysis, ICP-MS, electron probe microanalysis, scanning electron microscopy, and LA-ICP-MS (Analytical Center for multi-elemental and isotope research SB RAS). Results and conclusions. The Zhaman-Koitass massif is composed by A-type subalkaline leucogranites (SiO₂ = 72.8–75.4 wt %, Na₂O + K₂O = 7.5–8.8 wt %, K₂O/Na₂O = 1.11–1.25, ∑REE = 120–231 ppm, (La/Yb)n = 10–22, Eu/Eu* = 0.2–0.4), which are characterized by titanite-ilmenite-magnetite accessory specialization. U-Pb isotope dating confirms the silurian age of the Zhaman-Koitass granite-leucogranites (426–420 Ma). The obtained geochronological data, along with the similarity of the chemical composition of the rocks, confirm that the granite-leucogranites of the Zhaman-Koitass massif belong to the Borovsk complex. The significant age interval between the ordovician granitoids of the krykkuduk complex (448 ± 2 Ma) and the silurian granite-leucogranites of the karabulak and borovsk complexes considered in the article (431–426 Ma) suggests a change in the geodynamic situation from suprasubduction to transform marginal-continental.

Research subject. The geological profile of Sukadana Basalt Province as a large basalt outcrop in the back arc of Sumatra remains to be unclear. This also concerns the geological structures and their relationship with the Sundaland regional geology. Aim. To reveal the type and pattern of geological structures that controlled the Sukadana Basalt Province (SBP) to the surface, the distribution of Sukadana Basalt on subsurface and its relationship with Sundaland regional tectonics. Materials and Methods. A reprocessed bouguer anomaly map of Tanjungkarang quadrangle 1991 was used. Results. We found that the main eruption was located in the center of SBP. The forward modeling data show the thickness of SBP to reach 3,200 m. There are two Northwest-Southeast striking normal faults and one fissure controlling the development of SBP. These fractures served as the primary conduit for magma to ascend from the mantle to the Earth’s surface. We also found North-South striking normal faults and West-East dextral strike-slip fault that formed at Early Oligocene and indirectly supported the magma ascend to the surface. Conclusions. The North-South striking normal faults were correlated with the Sundaland oroclinal bending. These faults developed through the extrados zone, a large pull-apart area that caused the continental lithosphere to become thinner. Meanwhile, Quaternary-Northwest-Southeast striking fractures are correlated with the development of the Great Sumatra Fault. The formation of Northwest-Southeast striking fractures was affected by the Great Sumatra Fault movement, and the thinning of the back-arc crust affected by multi-extensional structures was implicated in the ascend of SBP’s magma to the surface.

Subject research. Hypabyssal intrusive gabbro-dolerite-monzonite-granodiorite complex from the northern part of the Tagil megazone. Material and methods. Intrusive rocks situated among the Devonian strata of the East Tagil structural-formation zone at the North Urals were studied. Petrographic studies, silicate (XRF) analyses and determination of rare elements by ICP-MS method, study of U-Pb isotopic systematics in zircons from monzonites and quartz diorites, processing and interpretation of the data obtained using discrimination and spider diagrams, as well as indicator geochemical parameters were carried out. Results. It was found that the age and structural position of the studied rocks can correlate with the well-known Late Devonian Ivdel complex, differing from the typical composition of the latter by a significant content of rocks of medium and moderately acidic composition. The geochemical parameters demonstrate values characteristic of both suprasubduction (island-arc) and oceanic volcanites, which may indicate the formation of rocks of the studied complex in an environment of termination of the subduction process and separation of the subducted slab. The presence of significant volumes of diorites and monsodiorites is probably stimulated by contamination of crustal matter by the mantle melts. Conclusions. The obtained geological, petrographic, isotope-geochronological, and geochemical data do not contradict the model of separation of the subducted slab and the arrival of mantle highly depleted matter (close to oceanic basalts N-MORB) after the termination of the subduction process.

Research subject. The relationship of sulfide interlayers in silt-pelitic rocks with the cleavage of the axial surface at the Golets Vysochaishii gold-ore black-shale deposit (Bodaibo ore district). Methods. The structure of rocks was studied in out-crops, borehole cores, sanded samples, transparent and polished sections. The chemical composition of minerals was determined. Results. It was established that sulfide and sulfide-containing interlayers undergo deformation and recrystallization together with the host silt-pelitic rocks during plastic dynamometamorphic transformations of rocks. Conclusions. Metamorphic transformations of rocks took place in two stages. During the folding-thrust deformations of the first stage, a cleavage of rocks is formed, which leads to the splintering of sulfide interlayers with the orientation of the lenses along the cleavage. Metamorphic transformations of the second stage are manifested in sulfide and sulfide-containing interlayers in the collective recrystallization of their composing minerals with the replacement of surrounding rocks deformed at the previous stage. The second stage is characterized by changes in the mineral composition of rocks, manifested in the substitution of pyrrhotite with pyrite, increase in the iron content of chlorites and carbonates.

Research subject. Spatial distribution of bioavailable strontium in the South Trans-Urals. Aim. Development and test of a methodology for obtaining a bioavailable strontium map suitable for studying migrations and mobility in the Bronze Age in the Southern Trans-Urals. Methods. Sampling was conducted in 73 loci located in a uniform network in a 25 ± 5 km grid and in 22 additional loci (transects along the intermediate lines in places of complex geological structure). The determination of strontium content was carried out by the ICP-MS method. The strontium isotope composition was measured using an inductively coupled plasma magneto-sector multi-collector mass spectrometer (MC-ICP-MS). Statistical methods included analysis with stem-and-leaf plots; Student’s t-test; ordinary kriging (the mean is unknown) with linear semivariogram; analysis of correlation according to Pearson’s test. Results. The surveyed area is 36 sq. km². The sample size is 357. Samples for different types have similar mean and median values; the differences occur in the fourth fractional digit. Criterion 1 (n ≥ 0.001) can be used to determine local variability, and Criterion 2 (0.706 < n < 0.716) can be used to assess the origin of ancient individuals, animals, and archaeological objects. The interpolated maps for each sample type were created. All bioavailable strontium maps show similar spatial patterns. Cross-validation revealed areas of the lowest accuracy. Conclusions. The similarity of the distribution of anomalies on the maps of different types suggests the feasibility of the sampling technique. There is a clear tendency for the zones of elevated ⁸⁷Sr/⁸⁶Sr values to be associated with the older lithology (0.7106, mean). The lower values (0.7091 ± 0.002) are associated with the younger lithology. Given the complex geological structure and a wide range of rocks in the study area, a positive result is the low differentiation of the zoning of the identified anomalies, which correspond to large structural-formation zones of the Urals. The presented method demonstrates its suitability for studying sublatitudinal migrations of the ancient population of the Southern Trans-Urals.

Research subject. Selenium mineralization in altered rocks of the Gaisky deposit. Aim. Determination of formation conditions of native selenium in altered rocks. Results. Selenium mineralization is established in three zones of altered rocks in the sides of the 3rd quarry and is confined to the upper part of the sulfur-quartz rocks. Layers with a high content of native selenium and tiemannite are distinguished by a carbon-black color against the general background of yellow-green sulfur-quartz rocks, forming subvertical trickle textures. The maximum propagation of selenium mineralization was found in the southwestern zone of the quarry. Here, selenium-containing rocks are traced vertically by 6 m, forming a lens with a diameter of up to 70 cm. The accumulation of selenium occurs due to its physical properties. Selenium is similar to sulfur in volatility, although it undergoes more intense condensation under decreased temperatures. The accumulation of selenium condensate is facilitated by a silicic acid gel, which prevents the removal of selenium by a hydrothermal flow. Conclusion. The native selenium of the Gaisky deposit is characterized by a hydrothermal genesis, which, along with the presence of monoclinic native sulfur in the rocks, indicates the hydrothermal formation of the entire complex of altered rocks.