Volume 519, Nº 1 (2024)

Data on the absolute value of the geomagnetic field intensity at the beginning of the Cretaceous Normal Superchron (C34n) was obtained from basalts of Hooker Island of the Franz Josef Land archipelago (FJL). These basalts are considered as one of the manifestations of the High Arctic Large Igneous Province. The record of the ancient geomagnetic field in the studied Early Cretaceous basalts was preserved well due to the presence of pseudo-single domain grains of primary magmatic titanomagnetite. The paleointensity, obtained by the Thellier–Coe method, satisfies the generally accepted reliability criteria, taking into consideration other necessary evidence. This information indicates that 125 Ma, during the formation of the FJL traps, the intensity of the geomagnetic field was four times lower than today. Our estimates show that the mean value of the virtual dipole moment was 1.7 × 10²² Am². These results support the views about the low paleointensity at the Barremian–Aptian boundary and indicate a correlation between the intensity of the geomagnetic field, the frequency of reversals, and the formation of mantle plumes.

New isotopic data presented in this paper have made it possible to determine the stratigraphic position of the Talinskaya Formation in the regional stratigraphic scale of the Early Precambrian. The U-Th-Pb age of 1926±7 Ma obtained for metariodacites of the Talinskaya Formation for the first time () indicates that this formation is coeval to the Kaskamakaya Formation, which, together with a similar isotope-geochemical composition of the type varieties of the Kaskamskaya and Talinskaya formations (komatiite basalts, aluminous metabasalts, and metariodacites), significantly expands the understanding of the size of the area which is composed of the Paleoproterozoic Kalevian Superhorizon in the Kola-Norwegian region of the Fennoscandian shield.

The Rb–Sr age of gluconite and the U–Pb LA–ICP–MS age of detrital zircon from sandstones of the Riphean Okos Formation and the Vendian Ust-Pinega Formation were determined in the Keltmen-1 parametric borehole, drilled in the Vychegda trough of the Mezen syneclise in the European north of Russia. The model Rb–Sr age of glauconite (870–820 Ma) and the U–Pb age of the youngest detrital zircon (1005 ± 14 Ma) limit the time of accumulation of the Okos Formation to the first half of the Late Riphean, which is in good agreement with biostratigraphic data. The U–Pb age of the youngest detrital zircon obtained from the lower part of the Ust-Pinega Formation suggests that sedimentation of Late Vendian sandstones into the Mezen Basin began about 575 Ma. Thus, the duration of the stratigraphic break between the Riphean and Vendian is about 250–300 million years. In the Late Riphean and Late Vendian times, the Mezen basin was filled with terrigenous material of Archean–Late Proterozoic age (from 3.25 to 1.02 billion years), the sources of which were rocks of the Baltic Shield. In the lower part of the Ust-Pinega Formation, a population of detrital zircon of Vendian age (730–575 Ma) was discovered, a possible source of which could be rocks of the Proto-Ural-Timan Orogen.

A thermodynamic model of the ternary fluid system H₂O-LiCl-NaCl is proposed for the temperature range from –77 to +300°C. This model incorporates low-temperature phase transitions of freezing products of water-salt inclusions. The model is based on the Pitzer equations using new interaction parameters of Na, Cl and the corresponding equilibrium constants of reactions involving the solid and liquid phases. Based on microthermometry data of fluid inclusions (T of phase transitions during heating after freezing), the model allows determine the salt concentrations. Characteristics (T, wt% LiCl and NaCl) of triple points with solid phases including the eutectic E''(ice + LiCl·5H₂O + NaCl·2H₂O), peritectic ${\text{P}}_1^{\text{''}}$ (LiCl·5H₂O + + NaCl·2H₂O + NaCl) and ${\text{P}}_2^{\text{''}}$ (LiCl·5H₂O + LiCl·3H₂O + NaCl) and cotectic, peritectic curves separating the phase fields (ice + L, NaCl·2H₂O + L, NaCl + L), as well as solubility isotherms of ice, hydrohalite and halite calculated by the model showed good agreement with experimental data. As an example of the application of the model to the natural object, we determined the salt contents in lithium-bearing brine inclusions in late quartz veins of the Bolshie Keivy area (Fennoscandian Shield).

The paper characterizes specific gabbro, the main rock-forming mineral of which is fassaite – alumina-rich (up to 12% Al₂O₃) calcium pyroxene, typical for high-temperature metasomatic rocks. In terms of geochemical characteristics, the fassaite gabbro are close to the subalkaline monzogabbro of the Ust-Krestovsky complex, which are widely distributed within the Krestovsky subterrane of the Olkhon terrane (Western Baikal region). At the same time, they differ sharply from the latter in terms of higher content of CaO and MgO and lower content of SiO₂ and Al₂O₃. Fassaite gabbro form several small massifs framed by the Ust-Krestovsky monzogabbro massif, without contacting the latter. A model of the formation of fassaite gabbros due to the assimilation of carbonate material (crustal carbonate melting) by subalkaline mafic magma is proposed.

Samples of siliceous rocks of the South Kambalny Central Thermal Field (SKC), containing unique ore mineralization, were studied. Optical microscopy, scanning electron microscopy, X-ray microanalysis, X-ray phase analysis, ICP-MS and Raman spectroscopy were used for the study. High concentrations and a wide range of rare and rare earth elements have been found in siliceous rocks. Silicaminerals (quartz, moganite, cristobalite tridymite opal), oxides (hematite, anatase), hydroxides (goethite), carbonates (calcite with Fe and Mn impurities), sulfates (barite with Sr impurities, gypsum), sulfides (pyrite, marcasite, chalcopyrite, chalcocite), phosphates (xenotime-Y, YPO₄ with impurities of lanthanides, S, Ca and As; aluminophosphate, AlPO₄ with impurities of V) and apatite have been identified. Structures of anatase replacement by quartz often in association with pyrite have been identified. The mineralization of siliceous rocks of the SKC reflects the physicochemical specificity of deep metal-bearing solutions.

The structures of two potassium richterite crystals with crystal chemical formulas (K_0.44Na_0.32□_0.24)_Σ=1(Ca_1.18Na_0.82) were studied by single-crystal X-ray diffraction analysis and Raman spectroscopy (RAMAN)_Σ=2Mg₅Si₈O₂₂OH₂ and (K_0.83Na_0.02□_0.15)_Σ=1(Ca_1.18Na_0.89)_Σ=2Mg₅Si₈O₂₂OH₂ synthesized at a pressure of 3 GPa and a temperature of 1000°C in the MgSiO₃+CaMgSi₂O₆+K₂CO₃+Na₂CO₃+CO₂+ +H₂O system. The parameters of monoclinic cells are obtained: a=10.0256(5) & 9.9748(11), b=17.9874(7) & 17.9879(16), c=5.2687(3) & 5.2746(6) Å, V_u.c. = 916.17(18) & 918.52(8) Å3, β = 104.520(12)^o & 104.821(5)^o, sp. gr. С2/m (12), Z = 2. It was found that positions M(1), M(2) and M(3) are inhabited by Mg²⁺, position M(4) is occupied simultaneously by Ca²⁺ and Na⁺. The Na⁺ cations that are not included in M(4) are located in position A, which also accommodates K⁺ cations. Raman spectroscopy showed the presence of vacancies in position A in both samples. The structure corresponds to the “ideal” structure of richterite group minerals. The unit cell volumes of the measured crystals are directly proportional to the content of K in position A. Based on the generalization of new and published data, an equation of dependence of V_u.c. fоr amphiboles of the richterite Na(NaCa)Mg₅Si₈O₂₂(OH)₂–K-richterite K(NaCa)Mg₅Si₈O₂₂(OH)₂ series with a low tremolite component on the K content in position A is proposed.

The existence of vegetation of open environments with a predominance of grass-forbs meadow associations and the participation of pine-oak forests was reconstructed on the basis of the study of microphytofossils from the Lower Pleistocene deposits of the Taurida cave in central Crimea. These results are consistent with data on the composition of land vertebrates from the Taurida locality. The studied spectrum demonstrates similarity with the spore-pollen assemblage of the Berezan horizon of Ukraine with a maximum age of about 1.8 Ma. Based on the abundance of trichomes and plant fibers similar to those of Ficus carica Linnaeus, 1753 in the coprolites, it is assumed that the extinct hyenas Pachycrocuta brevirostris (Gervais, 1850) ate fig fruits in certain seasons.

The article presents the results of the first high-precision route aerogravimetric survey, carried out in 2023 along the “cross” profile of Lake Baikal at a flight altitude of 5300 meters. The airborne gravimetric complex used in the measurements, based on the laboratory's AN-26BRL aircraft, is described. Directly above the lake water area, the largest negative value of the measured gravity field anomaly was -180.8 mGal, the horizontal gradient of the field measurement along the profile was up to 9 mGal/km in the area of the western and up to 5 mGal/km in the area of the eastern shores of Lake Baikal. The internal convergence of anomaly values on the route profile for a complex of three instruments was 0.74 mGal. For the Baikal Rift Basin, the resolution and reliability of the most current modern global models of the Earth's gravity field UGM-SGG-2, EGM2008, XGM2019 and Sandwell and Smith v32, based on satellite data, were assessed. It is shown that the standard deviations of the field along the entire profile between the values calculated from satellite models with the number of expansion coefficients of 2190 or more from airborne gravimetric observations are 9.5 - 17.9 mGal, and the maximum deviations at individual points of the route are 40-80 mGal. Using airborne gravity profile data, a comparison was made with marine gravity survey data at a scale of 1:500,000. Due to the high detail of the data along the airborne gravity profile, it was determined that the actual value of the main negative anomaly on the airborne profile is higher than that accepted for the analysis and integrated interpretation of geophysical data in the area of Lake Baikal.

It is proposed in this paper to use the focal characteristics of small seismic events, in particular, the scaled energy and the rupture propagation velocity, as indicators of possible dynamic movements along a fault. The two sites selected for analysis underwent microseismic events induced by mining operations. The first site, the Korobkovskoe iron ore deposit of the Kursk Magnetic Anomaly, is located in the aseismic region. The second site, the apatite–nepheline deposit of the Khibiny massif, is characterized by relatively intensive natural and human-triggered seismicity. Based on the results of the analysis, the values of the scaled seismic energy and the rupture propagation velocity are drastically different at the deposits under consideration. At the apatite–nepheline ore deposit, the parameter values are close to the range of values characteristic for “normal” earthquakes. At the KMA deposit, the obtained anomalously low values of the scaled energy and the rupture propagation velocity correspond to “slow” earthquakes. The results obtained are indicative of the prospects for using the selected parameters as indicators of possible large dynamic events at the studied site of the fault zone.

Using statistical properties of the solution of the Fokker-Planck-Kolmogorov equation (FPC) for velocities and coordinates, and using the vortex identification method, quantitative estimates of the distributions of various characteristics of cyclones and anticyclones (including lifetime, wind speed, size, characteristic forcing, and kinetic energy) as a function of their intensity have been obtained. The calculations are based on ERA5 reanalysis data for the period 2010–2021. The vortex lifetimes estimated using the FPC correspond to the lifetimes obtained using the vortex identification method, and the theoretical distribution of cyclones by intensity practically coincides with the observed ones. The characteristics of vortices during their life cycle are also investigated. In general, all analysed characteristics of cyclones increase with their intensification. But for intense anticyclones the increase is not as pronounced as for cyclones.

Soil respiration (SR) is one of the largest fluxes in the global carbon cycle, exceeding anthropogenic CO₂ emissions by more than an order of magnitude. Estimation of the heterotrophic component of SR is necessary to assess the carbon balance at ecosystem, regional, national and global scales. Within the framework of the Most Important National Innovation Project “Development of the system of ground and remote monitoring of carbon pools and greenhouse gas fluxes on the territory of the Russian Federation” the first Russian national network of CO₂ emission from soils is organized. For the first time on the entire territory of Russia on the basis of methodologically unified SR field measurements were conducted. This study combines first measurements conducted in the summer period (June – August) of 2023 at 75 monitoring sites in different ecosystems in the main Russian bioclimatic zones from tundra to semi-desert. SR values and its relationship with the temperature of the upper 5–10-cm layer of soil (Ts) were analyzed. Positive effect of soil temperature on mean summer SR rate and maximum monthly SR values is observed in the interval of mean Ts from 10 to 20°C. Among the studied ecosystems, the lowest SR values were found in tundra and bog ecosystems, while the highest values were found in forest-steppe. Amongst forest ecosystems, the lowest SR rates are characteristic of larch forests, while the highest SR values were observed in broad-leaved forests of the forest-steppe zone. To clarify the obtained regularities, it is necessary to expand studies in all bioclimatic zones, but mainly in agrocenoses, tundra and steppe ecosystems.

Over the seventy-year period of the Don river valley flood control under conditions of a lack of water climatic cycle, irreversible geomorphological and biogeocenotic transformations occurred in the drainage basin. As a result of persistent avalanche sedimentation, the Don delta and the seaside of the Taganrog Bay became shallow. During strong easterly winds, the seabed near Taganrog, from Port Katon and from Zaimo-Obriv is sewed over a distance of 5–10 km or more. In the winter of 2023–2024, a unique phenomenon of activity and accumulation of carp and sazan in the Don River delta was noted. Clearly abnormal mass accumulations of valuable commercial species, their early maturation, can be associated with the action of a complex of factors that were provoked by increased water discharge from the Tsimlyansk reservoir. The flow of water with fish mass along the Krivoe and Svinoe arms, at an extreme water negative setup, came up against a sandbar, which reflects the effect of shallowing of the Don River after 1952.