Home – Home – Jornals – Russian Geology and Geophysics 2026 number 5

This article presents a review of the results from a comprehensive study and dating of contourite deposits in the southwestern Atlantic. It focuses on identifying the sources and transport processes of sedimentary material in the context of Pliocene-Quaternary environmental and climatic changes. The primary emphasis is on research conducted by the Laboratory of Paleoceanography at the Shirshov Institute of Oceanology RAS in collaboration with colleagues over the past decade. The contourite systems examined include those on the continental slope of Argentinian Patagonia, the Santa Catarina and São Paulo plateaus, the Ioffe Drift, and the gravitite-contourite system at the base of São Tomé Seamount. The identification of these systems is based on a comprehensive set of seismoacoustic, lithological, and geochemical data, including variations in magnetic susceptibility. Diagnostic features that distinguish contourites from other types of bottom sediments are discussed. The age of the sediments is determined using biostratigraphy or oxygen isotope stratigraphy and corroborated by accelerator mass spectrometry radiocarbon dating for the last 50,000 years. It is demonstrated that the primary agent in the formation of these contourite systems is the erosional and depositional activity of bottom (along-slope) currents of Antarctic origin, which are a key component of the Atlantic meridional circulation and the global ocean conveyor belt. Consequently, contourite systems preserve a record of the geological and climatic history of the region. Among all the systems considered in this study, the Ioffe Drift contains the oldest sediments, which have accumulated over the last 3.2 Ma. This interval corresponds to the period of modern-type paleoceanographic variability that followed the closure of the Panama Seaway. For the other systems, the sediment cores characterize the glacial-interglacial stages of the Late Quaternary and the associated changes in sea level, climate, and bottom-water circulation.

We have conducted petrological, geochemical, and geochronological research on gabbro intrusions of the Utlyktash complex in the northern part of the West Magnitogorsk zone in the Southern Urals. The studied intrusions are confined to the wings of the Imangulovo syncline formed due to the syncollisional setting and to its surroundings. According to new LA-ICP-MS data, the age of the Uraz gabbro massif is 333 ± 3 Ma. The geochemical features and Nd-Sr isotopic composition of the Utlyktash complex indicate that a weakly depleted PM-type mantle is a source for gabbroids with subsequent significant magma fractionation and minor crustal assimilation (up to 6%). Thermodynamic modeling supports the fractionation model of a single parental melt from which all the studied gabbro bodies crystallized. The ID-TIMS and LA-ICP-MS U-Pb zircon dating (ranging from 0.44 to 2.73 Ga) has revealed the involvement of ancient continental crust and ophiolitic material from the Main Ural fault zone, along which the Magnitogorsk island-arc terrane was thrust onto the Laurussia paleomargin. The geological position of the Utlyktash complex and its geochemical correlation with basalts from the central part of the Magnitogorsk megazone suggest its formation during syncollisional rifting in the early Carboniferous, preceding the assembly of the Laurasia supercontinent.

Metasedimentary melange in the Mt. Sulu-Tyube area bears fine- and medium-grained eclogites, which are predominant within the Kokchetav subduction-collision zone (Kazakhstan), along with scarce porphyroblastic eclogites juxtaposed with rocks of the Zerenda Group. The assemblage of garnet cores ( X _Alm ≤ 0.59, X_Prp > 0.08) with epidote-clinozoisite ( X _Czo = 0.36-0.90), amphibole, ilmenite, titanite, and rutile and the prograde zoning of garnet suggest the nearly isothermal burial of rocks at 11.5-20.5 kbar and 535-570 °С. The growth of high-Mg garnet rims ( X _Prp ≤ 0.31) in paragenesis with omphacite ( X _Jd ≤ 0.35) marks the second stage with nearly isobaric heating up to 645 °С at 21.5 kbar and to 620-690 °С for some samples. Fine- and medium-grained eclogites with uniform structures and with weak zoning of garnet containing omphacite ( X _Jd = 0.20-0.40), rutile, and quartz inclusions formed during heating and limited pressure increase This article presents new data on ore mineral microinclusions and the ore element content of Kamchatka adakites associated with melting of oceanic lithosphere of varying ages in the transition zone from the Pacific Ocean to the Asian continent. Based on these data, hypotheses are made regarding the generation patterns of metalliferous adakites and their role in the formation of copper-gold-silver mineralization in the region. (580-660 °С and 16-19 kbar). Variations in equilibrium temperatures (620-730 °С) indicate their different positions within the subducted lithosphere. The eclogites are similar in signatures to MORB and correspond to low-Ti tholeiitic rocks, but the fine-grained rocks are depleted in Nb, Ta, and Eu and enriched in Th and are characterized by a radiogenic isotopic composition of Sr (⁸⁷Sr/⁸⁶Sr_i = 0.71181-0.72935) and moderately depleted Nd isotopes (ε_Nd(530) = 0.5-4.2), whereas porphyroblastic rocks rehydrated during exhumation show juvenile Nd-Sr signatures (⁸⁷Sr/⁸⁶Sr_i = 0.70212-0.70426, ε_Nd(530) = 6.6-7.2). The contrasting features of eclogites result from the subduction of the rift-related margin of the Kokchetav microcontinent or a more ancient continental structure including variably contaminated N-MORB- and E-MORB-type basites and from the involvement of oceanic or eroded Cambrian island arc rocks in the same process. The differences in the fluid regimes of subduction and exhumation were due to the proximity of a hydrated subduction channel for porphyroblastic eclogites and to the weak fluid permeability of continental lithosphere for fine- and medium-grained eclogites.

We present a thermodynamic model of the interaction between surface water and the flotation tailings of PGE-Cu-Ni sulfide ores from the studied ore district in the Krasnoyarsk Territory. The urgency of the study is determined by the need to assess the long-term stability of mineral assemblages. The aim of the study is to elucidate the regularities of transformation of mineral assemblages during long-term storage. The mineral and chemical compositions of samples from two pits and the chemical composition of aqueous extracts served as initial data. Calculations were carried out in the solid-water-gas system with varying Eh values to simulate different degrees of the system openness to atmospheric oxygen (standard P - T conditions, pCO_{2 gas} = 10^-3.5 atm). Based on the modeling results, it has been established that pyrrhotite remains stable under extremely reducing conditions ( pO_{2 gas} = 10^-79 atm), in which the dissociation of water into atomic oxygen and hydrogen is possible. In general, the obtained models reflect the transition from sulfide to oxide-silicate assemblages, accompanied by a decrease in the number of mineral phases as oxidation progresses. The modeled assemblages are consistent with the parageneses observed in the polished sections. It is shown that the material largely retains its primary mineralogical features even after decades of storage, which is explained by the high content of rock-forming minerals within a dense clay matrix that prevents penetration of oxygen and moisture in amounts sufficient for intense oxidation. The results obtained can be used in the development of technological schemes for the recovery of potentially valuable metals from flotation tailings of PGE-Cu-Ni sulfide ores.

This paper analyzes published data and brachiopod collections available to the authors to determine the systematic composition of brachiopods of the subphylum Rhynchonelliformea from the Cambrian formations of the Siberian Platform. To date, 50 species and 1 taxon identified to the genus level ( Finkelnburgia sp.) have been described. These belong to 15 genera, 10 families (family assignment for two genera remains unclear), and 5 classes. Cambrian brachiopods of the subphylum Rhynchonelliformea from the Siberian Platform can be divided into six associations, each characterized by a specific taxonomic composition, paleogeographic distribution, and stratigraphic range. The most representative brachiopods belong to the class Obolellata. Specimens of this class have been found in North America and Greenland, allowing for relatively confident correlation of Lower Cambrian deposits between North America and the Siberian Platform. The class Strophomenata is also widely distributed. However, of the ten Siberian species of the genus Billingsella Hall & Clarke, eight are endemic. Thus, the occurrences of these brachiopods can be effectively used for genus-level correlation of transitional strata between the Middle and Upper Cambrian. Representatives of other classes (Chileata, Kutorginata, and Rhynchonellata) have lower potential for interregional correlation, although some of them have been found in other regions of the world and can serve as additional tools for correlating distant sections.

The Severo-Ketskaya parametric well was drilled by AO NPC Nedra to a depth of 5200 m in the period 2021-2023. The well is located in the southwestern part of the Pre-Yenisei sedimentary basin in the dome zone of the large anticlinal structure of the same name, buried under the Meso-Cenozoic cover. The well uncovered a new carbonate-terrigenous section of the Vendian and carbonate deposits, presumably of Riphean age, for the Pre-Yenisei sedimentary basin. The article substantiates the stratigraphic boundaries of the Vendian on the basis of geophysical correlations with typical sections of the south-west Siberian Platform, presents the general lithological characteristics of the Vendian section and the exposed part of the Riphean (?). According to the data of the preliminary core study, the results of geophysical studies and tests of objects, the deposits of the Upper and Middle Danilovsky subhorizons are the most promising for oil and gas accumulation in the Vendian rock formations in the borehole drilling area. The results of geochemical studies of sections of parametric wells do not allow us to associate high oil and gas potential with the Proterozoic deposits of the Pre-Yenisei sedimentary basin.

We present the fundamental principles of our technology - GeoArrhenius/SpectrOptim for the justification and reconstruction of compositional kinetic spectra. The advantage of this technology is the reliable separation of gaseous hydrocarbons on the chromatogram and the reconstruction of multicomponent (with an arbitrary number of components) kinetic spectra at the early catagenesis based on neural network modeling. Applying this technology in hydrocarbon system modeling provides the opportunity to accurately assess the volumes of hydrocarbons generated by a source rock and consequently enables the evaluation of hydrocarbon resources in an exploration area. This approach reduces the reliance on external and internal analogies during calculations, as well as the expert opinions of geological researchers.