Vol 511, No 1 (2023)

Within the Sikhote-Alin orogenic belt, a new promising type of mineral resources has been identified – complex ores and placers spatially and genetically related to Late Mesozoic ultramafic intrusions. An example of this is the Ariadne massif of ultramafic rocks, in the center of which there is a manifestation of gold-titanium mineralization, and in the exocontact – gold-antimony. The main features of the mineralogy and geochemistry of gold-copper formations in its near-intrusive zone are determined. To reconstruct the conditions for the formation of these ores, the isotopic composition of sulfur in sulfide minerals was studied. The obtained materials testify to the significant metal-bearing potential of the ultramafic rocks of the Sikhote-Alin.

Within the northern part of the Tagil paleo-island-arc structure in the Northern Urals, the Sosva-Lozva graben is identified. The graben is filled mainly with terrigenous and volcanic strata of the Devonian and Lower Carboniferous. The location of the graben to the west (in modern coordinates) of the supra-subduction magmatic complexes and the composition of volcanic rocks, which combines signs of igneous formations of convergent and divergent settings, suggest that this structure formed under extensional conditions in the rear of the active continental margin.

During hydrogeochemical testing of the Mogoisky thermal spring in Northern Transbaikalia, 5 samples of modern mineral sediments were taken, in two of which opal is the main component of geyserite, and in the other three carbonates, fluorides and sodium sulfates predominated. Calculations of deep temperatures showed that the formation of geyserite is associated with low-temperature hydrotherms and is explained by a decrease in their temperatures during discharge. Deposits of easily soluble salt minerals occur on the evaporation barrier, during rainy periods they can completely dissolve and disappear.

The article is devoted to the study of diamonds of the I and IV varieties (according to the classification of Y.L. Orlov) from Snap Lake kimberlites. Based on the study of the morphology, the impurity defects of nitrogen and the internal structure of these diamonds, it was found that the uncoated crystals and the cores of coated diamonds were formed under similar conditions. It is assumed that the coats were formed on a significant part of the formed diamonds under mantle conditions, and their etching occurred at the hypogenic stage of the development of the kimberlite body.

Melt inclusions in the minerals of a sample from a dolerite dike of the Vilyui-Markha dike swarm, located on the northwestern shoulder of the Vilyui paleorift, have been studied. Data on the composition of homogeneous glasses of melt inclusions in minerals made it possible to establish the PT-parameters of mantle sources of initial deep melts responsible for the formation of gabbro-dolerites of the Vilyui paleorift. Two levels of generation of initial melts for dolerites have been established: in the intervals of 95–65 km at 1480–1400°C and 55–45 km at 1360–1320°C. The presence of two intermediate chambers in the crust, where melts crystallized, was identified at depths of about 12 and 9–4 km with a decrease in temperature to 1175–1125°С. The two-level arrangement of magma generation centers, as well as the heterogeneity of the chemical composition of the studied minerals, makes it possible to explain the presence of two pulses of Devonian basic magmatism.

Geochemical study of volcaniclastic material and radiocarbon dating of charred plant debris from Holcene deposits of the Guram site, which is located in vicinity of Vetrovoy Isthmus at Iturup Island, demonstrate that explosive eruption (VEI 4-5) occurred there by 2000 years ago. Geochemical and age similarity with the tephra of marker layer CKr that was distinguished at Iturup, Urup, Simushir, Rasshua, and Matua islands of the Kuril Island Arc led to the conclusion that this eruption is supposedly a source of this tephra. The data presented are proposed as a motivation for revision of volcanic hazard at Iturup Island.

A vertical sequence of brachiopods was revealed at the base of the Verkhoyanian terrigenous complex of the Tit-Ary section in the northern part of the Tuorasis uplift of the lower reaches of the Lena River. As a result of the study of these brachiopods, it was established that in the indicated section, the Upper Cambrian dolomites are overlain by Gzhelian and Asselian deposits, characterized by brachiopods of the Jakutoproductus protoverkhoyanicus and Jakutoproductus verkhoyanicus biostratigraphic zones. This is the first proven fact of the presence of Upper Carboniferous deposits in the area. It is concluded that within the Tuorasis uplift from south to north, the upper age limit of the unconformity between the Cambrian and the Upper Paleozoic is growing older, while the base of the Verkhoyanian terrigenous complex is built up by the Permian basal beds and the Gzhelian deposits of the Upper Pennsylvanian. The Tit-Ary section is the first of those established in the lower reaches of the Lena River, with exposed boundary Carboniferous-Permian beds.

Using the data of magnetic observations performed at the INTERMAGNET network observatories during the period of the double earthquake on March 16, 2022 (Japan), the global nature of the induced geomagnetic variations was demonstrated. Their synchronism and comparable amplitude over a wide range of distances from 210 km to ~10 000 km, the delay time relative to the considered seismic events (~55 min) and the predominant period of variations ~30 min indicate that the source is a geodynamo perturbed by the action of seismic waves propagating deep into the earth.

Satellite radar interferometry data made it possible to clearly map two faults, shear displacements along which caused catastrophic earthquakes on February 06, 2023 in Turkey. According to satellite data, the relative displacements of the sides of the East Anatolian Fault Zone (EAFZ), to which the first event with a magnitude of Mw 7.8 was associated, exceeded 5 m in the central segment. The rupture surface extends from the area of the Doğanyol-Sivris of 24.01.2020 Mw 6.7 earthquake in the north to the Mediterranean coast in the south, where the earthquake Mw 6.3 occurred on 20.02.2023. The second event of Mw 7.5 is associated with the Surgü-Çardak fault, and the relative displacements of its sides, according to satellite data, exceeded 7 m. The obtained displacement fields of the Earth’s surface were used to construct a model of the seismic rupture. The model is based on the solution [5], which defines displacements on the surface of a spherically stratified planet as a result of dip and strike displacements on a rectangular rupture located inside the sphere. Ignoring the spherical stratification of the planet leads to errors of up to 20%, especially in the presence of a large shear component [5]. Also, an error is introduced by ignoring sphericity when using the solution obtained for an elastic homogeneous half-space [6], as the US Geological Survey (USGS) did when building seismic rupture models for earthquakes in Turkey in 2023. The difference of our model is the detailed consideration of the fault geometry. For this purpose, the faults were approximated by 19 planes along the strike, divided into two levels along the dip. In the built model, shear displacements in the central segment of the EAFZ reached 12.7 m. In the southern segment of this rupture, the displacements are substantially smaller. It should be emphasized that we registered the displacements for the period from January 29 to February 10, 2023, i.e. together with coseismic ones, they also include postseismic displacements for 4 days after the main seismic events. The displacements on the rupture surface along the Surgü-Çardak fault, where an Mw 7.5 earthquake occurred, reached 10 m. The obtained results demonstrate, in particular, the efficiency of application of satellite radar interferometry in the operative study of catastrophic geodynamic phenomena and processes.

It is shown that the area of winter Siberian polynya in the Laptev Sea has a negative correlation with the Arctic oscillation index (AO) for the winter period. Using this, a transfer function has been developed that connects the variations of winter polynya (the time series of the winter AO) and the geochemical time series of bottom sediments accumulated during the instrumental period (1898–2018) in the zone of distribution of the Lena polynya. The influence of winter polynya on sedimentation is determined by the formation of highly saline and cold waters entering to the bottom horizons. During the summer and in subsequent seasons, they determine the stratification of the water column of the shelf and make it difficult to convection. As a result, an oxygen deficit is formed in the bottom horizons, and the bottom sediments are enriched with redox-sensitive elements of anoxic environments and depleted of redox-sensitive elements of oxide environments. Reconstructions using the developed transfer function of the polynya during the last three centuries showed that its active development increases the average annual air temperature in the adjacent areas, but multidirectional affects the duration of the ice-free period.

A new decomposition method (decomposition into N and U-waves) of infrasonic signals corresponding to partial reflection of N-wave sounding pulses from anisotropic atmospheric layers and recorded in areas of geometric shadow at large distances from explosions and volcanic eruptions is presented. The decomposition method makes it possible to determine the vertical gradients of the effective sound speed (sound speed plus wind speed in the direction of propagation) that are not available for determination by other methods.

The characteristics of the sea ice conditions in the Seas of the Russian Arctic during the period of satellite measurements were studied and quantitative estimates of their changes in the second half of the 21st century were made based on the results of the CMIP6 climate models’ ensemble using aggressive and moderate scenarios of anthropogenic forcing, SSP585 and SSP245 respectively. It has been revealed that the dates of closing (DOC) of the sea ice cover and the length of the open water season (LOWS) are in general successfully reproduced by the ensemble of models. It is shown that DOC on average over the studied Seas will be observed about forty days later under SSP245 scenario and two months later under SSP585 scenario in 2061–2080 compared to 1981–2020 period. At the same time, the increase of LOWS is more than two and a half months under SSP245 scenario and almost four months under SSP585 scenario. The most significant changes in DOC are expected in the north of the Barents and Kara Seas, as well as in the northwest of the Laptev Sea: 2–2.5 months and 2.5–3 months later for the SSP245 and SSP585 scenarios respectively.

In the work, the influence of water content in soil pastes on their viscosity was studied by the method of vibrational viscometry and changes in viscosity were explained from the standpoint of the structural organization of humic substances (HS) of soils. It was found that the viscosity of pastes prepared from sod-podzolic soil, with a decrease in their water content below 36%, increases to values of 4000–4200 MPa sec, and then practically does not change. This contradicted the existing ideas about the viscosity of suspensions, which should continuously increase with a decrease in the water content in them. This phenomenon was explained from the standpoint of the presence in the soil paste another component in addition to water and soil particles (aggregates and microaggregates) – supramolecular formations (SF) from soil HS, which can separate from soil gels and pass into a dispersion medium. According to the literature data, SF of HS exist in soils in the form of fractal clusters (F-clusters) consisting of particles-molecules. Due to the high stability of F-clusters, it is possible to assume that soil particles sliding along F-clusters in pastes, and a change in the thickness of the F-cluster layer through which sliding occurs may not significantly influence the viscosity of soil pastes. The data obtained during the study of the viscosity of soil pastes confirm the importance of F-clusters in the occurrence of soil properties.

On the example of the forests of the Oka basin, an experiment was carried out to numerically solve the dual task set by the Paris (2015) Agreement on climate change: to assess the absorption of CO₂ from the atmosphere by forest communities under current global warming and their adaptation to climate change. With the help of empirical-statistical modeling, the mechanisms of forest cover regulation of the carbon cycle are revealed, with the effect of mitigating the predicted warming. Assessments of the adaptive potential of forests and its role in carbon adsorption and conservation have been carried out. The proposed index of elastic-plastic functional stability of forest ecosystems was used as an indicator of adaptation. The role of forest sustainability as a direct environmental factor in the absorption of greenhouse gases has been statistically established. An unambiguous picture of a significant increase in the ecological resources of boreal and nemoral forests has been obtained – their adsorption capacity with an increase in adaptive potential. It has been established that during the predicted 100-year period, the overall elastic-plastic stability of forest formations in the region should increase, especially at the current rate of global warming. Due to this, a significant increase in the ability of boreal and, to a lesser extent, nemoral forests to absorb greenhouse gases should also be expected. The obtained results of regional predictive modeling demonstrate the effectiveness of the coupled study of the adsorption capacity of forest biomes and their adaptation to a changing climate.

New results of the analysis of methane distribution in the troposphere over the Arctic shelf of Eurasia using satellite methods are presented. The main trends in the variability of methane content (increase), temperature (fluctuations without a pronounced trend) and ice cover for the period 2010–2022 are shown. Conclusions are made about the difference in the distributions of atmospheric methane over the western and eastern Eurasian Arctic, divided by the zone of the seismically active lineament of the Gakkel Ridge. It is shown that hydrometeorological parameters, including temperature and ice formation, are probably not the main factors for increasing the methane content in the atmosphere of the Eurasian Arctic shelf. The increase in methane content is associated with regional factors that are widespread over vast areas, such are, first of all, geological structures: oil and gas basins and tectonic fragmentation of the lithosphere, which forms permeability zones.