Vol 519, No 2 (2024)

In the central part of the Bashkir meganticlinorium, mafic intrusive rocks of the Low-Titanium (LTi) type (< 1 wt. % TiO₂) represented by picrites, picrodolerites and metasomatic metapicrite rocks. Carbonate-talc, chlorite-quartz rocks with phlogopite, calcite and dolomite are formed after picrites. Phlogopite has been separates from the metasomatites. According to ⁴⁰Ar/³⁹Ar step-heating dating of phlogopite, a plateau age of 1356±16 Ma was obtained. Picrites presumably have undergone metasomatism associated with early post-magmatic processes. Metasomatic processes are not divorced in time from the intrusion of picrites. Similar age values are known for a number of mafic HTi-type intrusive in the north of the Bashkir meganticlinorium. The obtained data suggest that these two types formed synchronously, at least at the late stage of Mesoproterozoic magmatic activity.

We report new estimates of the intensity of the geomagnetic field strength for the Permian–Triassic boundary. Amid predominantly low virtual dipole moment values for that time in the Global Paleointensity Database, episodes of increased VDM up to 8.9 × 10²² Am² were recorded in the sections of the trap formation of the Kuznetsk depression, which do not conform to the Mesozoic Dipole Low concept. Analysis of data on changes in the value of the virtual dipole moment during the formation of the Siberian Large Igneous Province within the framework of modern magnetostratigraphic correlations indicates a persistently weak geomagnetic field only at the initial stage, when most of its Norilsk area was formed. A change in the geomagnetic mode is noted after ~800 thousand years at the level of subchron LT1n.1r (251.2–251.1 Ma) of the General Magnetostratigraphic Scale and was recorded in the basaltic andesite lava sheets of the Kuznetsk area. Low virtual dipole moment values from this time correspond to episodes of reversals, while the overall intensity was on average only slightly lower than today. Thus, the drop in paleointensity at the very beginning of the Triassic period was not caused by a major long-term change in the geodynamo, but was short-term and related to plume activity.

The isotopic age of rocks from the clinopyroxenite-wehrlite Porya Guba Complex hosting the Kolvitsa Fe-Ti-V deposit was determined for the first time. Sm–Nd age of the barren clinopyroxenites prevailing in a studied massif is 1858 ± 34 Ma (ε_Nd(T) = –1.5) and is considered as the emplacement time of the Porya Guba Complex, occurred after the peak of granulite metamorphism (1925–1915 Ma). Quenching zones found around xenoliths of granulites in clinopyroxenites indicate the emplacement of the complex into the cooled rocks of the Lapland-Kola orogen, which is consistent with the estimated time of its cooling (1880–1870 Ma, 450°, by rutile). Mineralized rocks, as inferred from active assimilation of granulite xenoliths, are formed at a late stage of the complex development: the age of mineralized pyroxenites enriched in platinum and palladium (0.8 g/t) is 1832±35 Ma (ε_Nd(T) = –2.0), while the age of titanomagnetite ore is 1823 ± 19 Ma (ε_Nd(T) = –2.5). Thus, the obtained isotopic data indicate that the emplacement of small ultramafic intrusions developed in the Kandalaksha-Kolvitsa granulites (Kolvitsa Melange) took place during the cooling stage of the Lapland-Kola orogen.

Physico-chemical factors favoring formation of greisen tin deposits are evaluated based on the original data on composition of melt and fluid inclusions in magmatic and ore-forming minerals from Tigrinoe tin-tungsten deposit, Russian Far-East, and on the literature. We show that for the granitoid-related deposits the factors include: relatively low-temperature and low-pressure (720–770 °C/0.7–2 kbar, 3–6 km) granites formed under reducing oxygen fugacity (fO₂ below fayalite-magnetite-quartz, QFM buffer), that is indicated by absence of magnetite/presence of ilmenite, and by reduced positive Ce-anomaly in magmatic zircon (1); low-salinity fluid inclusions in magmatic quartz (2); fluid inclusions with the СН₄/СО₂ ratio of 0.1–0.3 in the ore-vein minerals (3). A number of problems related to the origin of tin-tungsten deposit need further studies. In the first place, it concerns the role of fluorine in magmatic accumulation and hydrothermal transport of Sn. Partitioning of Sn and W between granite melt and fluids under reducing fO₂ below QFM buffer also has to be experimentally evaluated.

Data are presented on the content and composition of hydrocarbons: aliphatic (AHCs) and polycyclic aromatic hydrocarbons (PAHs) in Holocene sediments (undisturbed cores 0–30 cm) collected in the southwestern region of the Kara Sea (I part of cruise 89 of the R/V Akademik Mstislav Keldysh”, September 2022). It has been established that the distribution of hydrocarbons, unlike C_org, does not depend on the lithotype of bottom sediments, since in the gas-saturated zone, along with methane, the formation of high molecular weight hydrocarbons occurs. This leads to an increase in the proportion of AHCs (>1%) and PAHs (>1×10^–3%) in the composition of TOC, as well as a change in their distribution and composition in the sedimentary sequence. In the lower horizons of the columns, the composition of hydrocarbons becomes more autochthonous. Changes in redox-potential in sedimentary strata also affect the concentrations and composition of hydrocarbons.

For the first time, poorly-rounded gold of ore habit was found in intergrowth with quartz, feldspar, ilmenite, zircon and other minerals, along with well-rounded placer gold, when studying the mineralogical and geochemical features of native gold from the Cretaceous conglomerates of the central part of the Aldan-Stanovoy shield. However, upon detailed study, it was found that gold of ore habit belongs to gold of the pseudo-ore habit. This gold is characterized by a pitted-tubercular surface, “intergrowths” of gold with minerals of the host deposits and through holes. Discovery of gold of the pseudo-ore habit in the Cretaceous conglomerates indicates the transformation of placer gold as a result of diagenesis processes, and not the superimposed later ore mineralization. Gold of the pseudo-ore habit was previously discovered in the Devonian conglomerates of the Timan Ridge, as well as in the Jurassic and Permian conglomerates of the east of the Siberian Platform. Presence of such gold was the reason for searching for ore sources in the studied territories, which did not lead to positive results. In general, identification of gold of pseudo-ore habit in conglomerates of various ages from the Archean to the Cenozoic makes it possible to more correctly predict the formation of gold deposits and select search methods.

The dominance of the voles Lagurodon arankae (Kretzoi, 1954) and Allophaiomys deucalion Kretzoi, 1969 in the Early Pleistocene small mammalian fauna from the main bone-bearing level of the Taurida cave (central Crimea) allows dating this faunal association to the beginning of the Calabrian (about 1.8–1.6 Ma), and correlating it to the Late Villafranchian and the MQ1 zone of the European mammal biochronological scale, the second half of the Psekupsian Faunal Assemblage, and the regional mammal zone MQR10 (Allophaiomys deucalion – Prolagurus ternopolitanus zone). The lower part of the cave deposits was found to contain components of the more ancient regional mammal zone MQR11 (Allophaiomys deucalion – Borsodia zone), which dates to the terminal Gelasian. Thus, the Early Pleistocene phase of the formation of the Taurida locality corresponds to the time interval of about 2.1–1.6 Ma. The cave deposits also yield remains of Middle Pleistocene small mammals dominated by the vole Microtus ex gr. arvalis (Pallas, 1778). The evolutionary level of these associations suggests an age of the mid Middle Pleistocene (about 0.5–0.3 Ma) and correlation with the regional mammal zone MQR3 (Arvicola mosbachensis – Lagurus transiens zone).

Palynological data obtained from sediments that include the first find of the tusk fragment – Trogontherii elephant (Mammuthus trogontherii) in the Primorsky krai allowed us to reconstruct its living environment in the Middle Pleistocene. The reconstructed plant formations indicate warmer and drier climatic conditions during the existence of Mammuthus trogontherii in the southern Russian Far East than the modern ones. The ecosystems of the region had a more complex structure. Nemoral plants were more widely represented in them. Mesophilic pine-spruce forests with broadleaf trees and larch-birch sparse forests are presented the main appearance of landscapes. Shrubby birch and alder thickets, sparse larch-birch forests and sphagnum mires occupied plains and lakeshores.

The fundamental criterion for selecting the models of viscoelasticity for theoretical reproduction of unstable behavior of geosystems is the appropriateness of such models (with regard for extremely high inherent viscosity of geomaterials) for description of real wave processes in the same geosystems prior to the onset of instability. In the case of high viscosity, it is substantiated the fundamental inappropriateness of models of the Voigt type and the fundamental appropriateness of models of the type of standard viscoelastic material (with the particular case of the Maxwell model). It is proven that in the case of instability of the elastic comparison system, the instability of corresponding viscoelastic system develops dynamically, and even faster than the instability of the elastic comparison system.

The paper presents the results of modeling of the stress-strain state of the epicentral zone of the strong crustal earthquake Aketao, which occurred near Muji (China) on November 25, 2016 with magnitude M_w 6.6. The finite element method was used to model the stress-strain state of the epicentral zone with subsequent construction of stress intensity maps before and after the earthquake. The possibility to determine the location of rupture origin, its extent, including estimation of scalar seismic moment and earthquake magnitude is shown. For the first time the possibility to calculate the time function of seismic moment M_o(t) (seismic moment rate) based on the model of stress-strain state of rupture (earthquake origin) is presented, which allows to obtain synthetic seismograms and accelerograms of possible earthquake in the future.

A rare phenomenon – the long-range atmospheric transport of dust from the arid and semiarid territories of the Caspian Sea region through the center of European part of Russia to its Arctic areas – was registered in December 2023 during field study of aerosol composition aerosol in Moscow air and the snow composition in the Arkhangelsk region. The trajectories of air mass transport, dynamics of spatial and temporal variability of mass PM_2.5 and PM₁₀ concentration values in the Moscow region, as well as numerical estimates and spatial distributions of near-surface aerosol concentration and atmospheric optical characteristics over the European part of Russia (according to the MERRA-2 reanalysis) confirm an increase in aerosol air pollution due to long-rang air transport from the territories of the Caspian Sea to the Arkhangelsk region. In the snow sample taken in the area of Pinega (Pinezhsky Nature Reserve), Arkhangelsk region in the spring of 2024, in the thickness of the snow cover at an altitude of 18–20 cm (with a total snow thickness of 65 cm), a layer of snow that fell in December 2023 having a yellowish color was found. Preliminary studies of the sample of this snow showed the presence of a large amount of organic suspension and plant residues, which in winter indicates atmospheric aerosol transport from the southern regions of Russia.

One of the methods to increase the water stability and erosion resistance of soils is the use of polymer-structors. It is believed that the mechanism of their action is based on strengthening the bonds between the particles of clay minerals. This approach ignores the existence of organomineral gels on the surface of mineral particles, which can affect the effectiveness of polymers. The purpose of the work was to investigate the interaction of a number of structor substances used to increase water stability and erosion resistance with soil components. In model experiments on the interaction of polymers with soil components, suspensions of humate and bentonite were used. Verification of the results was carried out on leached chernozem. The effectiveness of polymers was evaluated by the blade method used to determine the water stability of soils, and the interaction of particles in suspensions in model experiments was evaluated by laser diffractometry. It was found that in solutions of humates with polymers, the size of particles formed in solutions increases with increasing hydrophobicity of polymers. No such unambiguous relationship was found in bentonite suspensions with polymers. Verification of the results of model experiments on chernozem showed that the water stability of the aggregates increases with an increase in the hydrophobicity of the polymer used for processing. To further verify the role of organic matter in ensuring soil water stability, an assessment was made of the possibility of using variously charged humic substances and iron sol to increase soil water stability. Experiments have shown that the use of iron sol increases the water stability of chernozem. Moreover, with an increase in the pH of the iron sol solution from 1.7 to 6.1, the effect value increases from 11 to 59%. The results of the study allow us to conclude that the shift in emphasis from strengthening the adhesion between mineral particles to strengthening organic and organomineral interactions should be considered as a reserve for increasing the effectiveness of formulations to maintain soil structure.

The article considers the bioaccumulation of elements in the organs and tissues of whitefish (Coregonus lavaretus L.) from various reaches of Lake Imandra with anthropogenic influence during the period of toxic load reduction. It is shown that the accumulation of elements in the organs and tissues of whitefish depends less on the concentrations in water and is determined more by tolerance to higher concentrations of toxic elements and physiological state. Models of element redistribution in the liver and kidney of whitefish depending on the physiological state of fish are constructed. The strategy of adaptive responses is most clearly manifested in changes in iron and zinc metabolism.

Research was conducted in 2023–2024 on the defining areas of the Belgorod region. Our research technique is conventional within the agrochemical service. The goal of this project was to study the specific activity of ⁴⁰natural and artificial radionuclides in soils and plants of certain agroecosystems. Studies have shown that specific activity does not vary significantly between leached arable (539 Bq/kg), typical (544 Bq/kg) and ordinary (573 Bq/kg), while in residual carbonate chernozems the value of said measurement (207 Bq/kg) was 2.60–2.77 times lower. The average specific activity of ²²³Th in leached, typical and ordinary chernozems was 1.97–2.35 times higher than the other residual carbonat chernozems. The average specific activity of Ra in studied soils did not differ significantly, staying within 17.3–18.9 Bq/kg. In soils of the region’s western areas, specific activity of ¹⁷³Cs ranged from 5,9 to 19,6, southern – 16.3–87.2 Bq/kg, while eastern sections of the region varied from 15.3–87.2 Bq/kg. Specific activity of ⁹⁰Sr in western soils was below 3, whereas the south extended from 16.3 to 87.2 Bq/kg. An average of ⁴⁰K specific activity altered from 111 Bq/kg to 597 Bq/kg was recorded within studied crop production, while ²³²Th’s and ²²⁶Ra’s ranges did not exceed 6 and 8 Bq/kg respectively. ¹³⁶Cs’ specific activity was less than 3, while ⁹⁰Sr stayed at less than 2 Bq/kg, which is significantly lower than the established limit for said parameter.