Volume 512, Nº 2 (2023)

The sedimentation interval (530–520 Ma) of the Teregtig Formation deposits in southern Tuva is estimated based on U–Pb dating of detrital zircons from terrigenous deposits and Sr-chemostratigraphy of carbonate rocks. The main source area for clastic material, containing a large amount of detrital zircon grains, were rocks with an age of 580 Ma. The presence of a wide diversity of Precambrian detrital zircons indicates that sedimentation of the Teregtig Formation took place within a block of continental crust with a long evolutionary history. The presence of numerous chromites in their matrix indicates that the rocks of the Agardag ophiolite complex were also part of the eroded land during the accumulation of conglomerates of the Teregtig Formation.

The paper presents new isotopic U–Pb zircon data (LA–ICP–MS method) on the intrusive rocks from the Chinorsai massif, which is spatially and probably genetically related to the large Jilau tungsten-gold deposit. This deposit, together with the other large Au deposits (Muruntau, Zarmitan, Kumtor, etc.) is part of the largest Au (Au–W) metallogenic belt of Tien Shan. The deposit is represented by small zones of scheelite-bearing skarn and later (overprinting) large stockwork of veins and veinlets with scheelite-gold mineralization that occurs within and near the intrusion. The concordant isotopic zircon U-Pb data (301.0 ± 2.6 Ma; MSWD = 2.6) are older than the isotopic zircon U–Pb data previously reported (about 288 Ma). This indicates a substantial extent of the magma emplacement and crystallization process that probably corresponded to several intrusive events or phases, which is a prerequisite for the formation of associated intrusive-related Au deposits. Also, the isotopic age determined highlights the earlier formation of gold-polymetallic-tungsten deposits as compared to Mo–W and Sn-W deposits in the region, which are related to the later Early Permian intrusions. In addition, zircon xenocrysts with much older age (from ca. 970 Ma to ca. 2200 Ma) have been identified; they probably represent the age of the orogenic basement including that of the basement terranes of the Tarim and Karakum cratons.

Laboratory model experiments have shown that peat, brown coal and its constituent organomineral components, as well as microscopic fungi isolated from brown coal, are characterized by a high potential for the extraction of all lanthanides from aqueous solutions. The processes of sorption of rare-earth elements by the components of organic matter proceed through the mechanisms of physical sorption, ion-exchange reactions involving carboxyl and hydroxyl groups, and complex formation involving –OH, –CO, and –COOH groups. SEM-EDS analysis revealed REE-containing mineral phases on fungal biomass, which are formed due to interaction with phosphorus- and nitrogen-containing functional groups of cell wall proteins. This indicates the participation of the biotic component in the formation of rare earth mineralization in brown coal deposits.

For the first time the δ¹⁸O values both in carbonate and non-carbonate (Ol, Phl, Mt) components of the rocks (calcite carbonatites, phoscorites, ijolites, turyaites) of the Kovdor massif were studied to clarify the role of contamination processes, retrograde exchange, and high-temperature fractionation in the igneous system. It has been established that the processes of crustal contamination are not recorded in the isotopic characteristics of the silicate part of the rocks, and the δ¹⁸О values of olivine, phlogopite, and magnetite are lowered compare to the compositions attributed to equilibrium with mantle peridotite. At the same time, the carbonate component of the rocks shows complementary enrichment in the ¹⁸O isotope with respect to the composition of derivatives of mantle melts. Estimates of the δ¹⁸О closure temperature of the olivine and the rates of rock cooling do not support the hypothesis of retrograde isotopic exchange. A hypothesis is proposed about the presence of a stage of redistribution of oxygen isotopes between the silicate and carbonate components of melts in the magmatic system, which took place before the formation of the Kovdor massif and its cooling. According to oxygen isotope data, the carbonate component could sharply predominate (1.5–4.5 times) over the silicate component during the equilibration.

The article describes the first find of authigenic carbonates on the southern flank of the Gakkel Ridge in the zone of its junction with the Laptev Sea continental margin of the Russian Federation. The samples are represented by dense magnesian calcites and aragonites, including rounded and angular fragments of terrigenous material, as well as microphytoplankton of different ages, spores and pollen of terrestrial and aquatic plants. Elemental and organochemical characteristics indicate the predominance of oxidizing or intermediate between oxidizing and reducing conditions of carbonate crystallization, which may be a consequence of their formation near the bottom surface. The isotopic composition of O, C, and Sr allows us to conclude that the diagenetic carbonates of the Gakkel Ridge were deposited mainly in isotopic equilibrium with bottom water at a temperature of about 0°C, which corresponds to measurements from the ship. A wide range of δ¹³С (–23.5 до –37.3) indicates that methane was an important, but not the only source of carbon in carbonates. The wide variations in the ⁸⁷Sr/⁸⁶Sr (0.70906–0.70933), which correlate with the δ¹³С values, show that the carbonate-forming fluid was not only modern sea water, but also diagenetic solutions coming from the sedimentary cover together with methane and the products of methane and organic matter oxidation. Intense discharge of heterogeneous methane-bearing fluids may be related to the high modern tectonic activity of the studied region.

A new, unusual Fe-free and As⁵⁺-enriched variety of chladniite, a rare phosphate of the fillowite group was found in exhalations of the active Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. It belongs to the high-temperature (500–750°С) paragenesis with calciojohillerite, fluorapatite, metathénardite, diopside, enstatite, forsterite and hematite. This genetic type is novel for fillowite-group minerals. The crystal  structure of Tolbachik chladniite is solved, R1 = 4.32%. It is trigonal, R–3, a = 14.9831(2), c = 42.8050(7) Å, V = 8322.1(3) ų. The structural formula is: ^M13(Na_{0.56\(\square \)0.44})\(_{2}^{{M21}}\)(Na_0.81Ca_0.19)\(_{2}^{{M31}}\) (Na_{0.97\(\square \)0.03})\(_{6}^{{M12}}\)(Ca_0.64Na_0.36)\(_{6}^{{M1}}\)Mn^M2(Mg_0.54Ca_0.46)^M3–9Mg\(_{{30}}^{{M10}}\)(Mg_0.94Ca_0.06)\(_{6}^{{M11}}\)Mg₆(P_33.53As_2.47)O₁₄₄ (Z = 3). The crystal chemical features of chladniite and their correlation with mode of occurrence are discussed for all chladniite findings known in meteorites and terrestrial objects of different genetic types.

To provide new insights into evolution of the primary ultramafic alkaline melts, we present an investigation of the primary and secondary melt inclusions within olivine macrocrysts and groundmass minerals from the Victoria monticellite-nepheline damtjernite, Anabar diamondiferous province, Siberia craton. The primary melt inclusions within olivine macrocrysts shown that initial damtjernite melts were K–Na bearing carbonate-silicate melts by composition whereas the K and Na associated within only silicate phases like that phlogopite, nepheline, kalsilite. That distinguishes these inclusions from similar inclusions in olivines from aillikites and kimberlites and emphasizes a more alkaline character of the damtjernitic parental melts. Based on the composition of melt inclusions within spinel and monticellite from magmaclastic groundmass, under the further evolution of the damtjernitic melts, K and Na are not only included in silicate daughter phases, but they can also form alkaline phosphates, carbonates, sulfates, and halides. That led to form the alkaline carbonate and saline sulfate-phosphate-chloride-carbonate liquids. This composition of the evolved ultramafic alkaline melt is common for melt inclusions within different minerals from aillikite, kimberlite and some carbonatites highlighted uniform mechanism of evolution of alkaline-ultramafic melts. Further accumulation of the fluid phase led to its reaction interaction with olivine with the formation of monticellite and degassing processes.

Mechanism of formation of large sedimentary basins on the continents is among the main problems in geodynamics. The formation of such structures far from convergent plate boundaries is most often explained by intense stretching of the lithospheric layer - rifting. This should be followed by a large and prolonged crustal subsidence due to cooling of the stretched lithosphere. A characteristic feature of the post-rift subsidence is a decrease in its rate in time - several times over a hundred million years. Rifting in the West Siberian Basin was associated with the formation of Permian-Triassic graben-rifts. The subsequent (post-rift) subsidence is considered by many researchers as a cause of formation of a thick layer of Mesozoic and Cenozoic sediments in the basin. Over the 86 Ma that passed from the beginning of the Middle Triassic to the end of the Middle Jurassic, the rate of post-rift subsidence should have decreased by about a factor of three. In fact, the opposite trend took place. Judging by the data of the Tyumen (SG-6) and En-Yakhin (SG-7) superdeep wells drilled in the north of the basin, the rate of crustal subsidence increased several times during this period of time. Such a sharp difference between the expected post-rift subsidence and the actual subsidence of the crust indicates that lithospheric stretching was not the main subsidence mechanism, and it could provide only a small part of the subsidence. Under such circumstances, the main cause of the subsidence should be contraction of rocks in the Earth’s crust due to prograde metamorphism.

At the initiative of the Federal Agency on Mineral Resources (Rosnedra), in August 2022, a shallow well was drilled in the East Siberian Sea for the first time with a purpose of geological studying the suture zone of deep waters of the Arctic Ocean and marginal structures of the continental shelf. The well was drilled by VSEGEI and Rosgeologia with the assistance of NK Rosneft and linked to the Rosneft’s long-term stratigraphic drilling program. Drilling was accompanied by continuous seismoacoustic profiling and well thermometry. The maximum well depth was 472 m from the bottom surface; in it, 147.5 m of core was taken to a depth of 268 m. Two sedimentary sequences were identified in the section: the lower Jurassic-Lower Cretaceous gently deformed sequence and the upper Neogene-Quaternary horizontally lying sequence. The sequences are separated by a thick unsampled interval with horizons of ascending thermal water. The Jurassic-Lower Cretaceous sequence occurs as a northwestern-dipping monocline, broken by faults and probably belongs to the complex filling the Zhokhov marginal trough of the Verkhoyansk -Chukotka orogen on the Eastern Arctic shelf.

Trace fossils and palaeopascichnids have been studied from the Basa Formation of the Vendian Asha Group of the South Urals (southwestern periphery of the Suleiman Anticline, Shubino quarry in the Ust’-Katav city, Chelyabinsk Region. The general morphology and preservation of ichnofossils was shown to be similar to the Late Vendian-Early Cambrian subhorizontal bilobate burrows of Didymaulichnus. The paleontological remains were found to be confined to extremely shallow depositional settings and located stratigraphically below the volcanic tuff layer, the zircon from which has a U–Pb isotopic age of 578 ± 7 Ma. Until now, the first occurrence of trace fossils and the associated “Agronomic Revolution” were thought to be timed to the interval of ~560–550 Ma. Our results show that mobile benthos and biological mixing of sediments may have occurred 20–30 Ma earlier and support the hypothesis that the onset of the first “Agronomic Revolution” and the “Cambrian Explosion” were not significantly coincident in time.

We present the data of instrumental observations made at the Mikhnevo geophysical observatory of the IDG RAS of magnetic field variations and the response of microbaric oscillations and the electric field in the Earth’s surface atmosphere to a strong magnetic storm on April 23, 2023 (Kp = 8). When determining the response of the ionosphere to a magnetic disturbance in the form of a change in the critical frequency of the F2 layer, we use the results of ionospheric sounding performed at the IAP (Leibniz-Institut Fur Atmospharen Physik). It is shown that during periods of maximum magnetic field variations, increased microbaric variations are recorded and increased electric field variations are noted. The magnetic storm was also accompanied by a change in the critical frequency f₀F2, as well as in the spectral characteristics of variations in the electric field strength.

The article discusses the results of seismoacoustic studies of the shelf of the southeastern part of Crimea, carried out in 2020–2023 by employees of the P.P. Shirshov Institute of Oceanology RAS an seismoacoustic profiler. The obtained data made it possible to refine the position of the paleovalleys, to perform a seismostratigraphic reference of the reflecting horizons with the identification of the main seismic complexes in the pleistocene-holocene part of the section. Seismic facies analysis of the wave field made it possible to clarify the paleogeographic conditions for the formation of paleovalleys.

The problem of far wave fields arising at the interface between ice and an infinitely deep homogeneous liquid in the flow around a localized source of perturbations is solved. An integral representation of the solution is obtained and, using the stationary phase method, an asymptotic representation of the solution is constructed for various modes of wave generation. Numerical calculations show that with a change in the flow velocities and ice thickness, a noticeable qualitative rearrangement of the phase patterns of the excited far wave fields at the interface between ice and liquid occurs.

Based on the analysis of the exist mechanisms of the hysteresis of soil water retention curve (WRC), as well as ideas about the nanostructural organization of soils, it is concluded that hysteresis can be caused either by stable (non-colloidal particles) or labile (gels) parts of the solid phase of soils. Due to the fact that until now the main attention has been paid to the study of the effect of stable solid phase of soils on the hysteresis of WRC, it was proposed to investigate the effect of soil gels on hysteresis. For this purpose, the effect of moisture content of soil samples prepared by drying and moistening on the initial viscosity of soil pastes was studied. It has been established that well-pronounced hysteresis is observed for samples of all studied soil types. To explain the hysteresis, two mechanisms based on changes in soil gels in the humidification-drying processes are proposed. One of them is based on the slowness of swelling and shrinkage of soil gels when they absorb and release water. The second is on the greater hydrophobicity of the surface of gels containing less water, and water slipping on hydrophobic areas of the surface with a decrease in the viscosity of pastes. Thus, the conducted studies have shown that hysteresis phenomena in soils are caused by soil gels and their changes during drying and moistening of soils.

Lack of water and regulation of the Don river runoff led to an irreversible transformation of natural hydrological and hydrochemical processes. At the end of 2022, despite of the shortage of river water, the region began laying a water pipeline to the Donbass, with a capacity of up to 300,000 cubic meters of water per day. Are there enough reserves of water resources for ever-increasing economic needs, throughout the year? The work is based on a targeted study of the chemical composition of water under different regimes and sea levels on the Taganrog coast of the Don Bay and Delta. The experiment covers the period from December 2, 2022 to January 30, 2023, and separate measurements, for comparison, on February 21; 30.03; 17.04.2023. Summary, three types of ionic composition were distinguished, which characterizes the Svinoe arm of the Don delta. Marine - with dominance (more than 80%) of summary amount of sodium and potassium ions, chlorides and salinity up to 7–9 g/L. The Don waters correspond to low mineralization (less than 2 g/l), an increased proportion of Na⁺ + K⁺ (50–60%), a close amount of SO\(_{4}^{{2 - }}\) and HCO\(_{3}^{ - }\) (30–40% each). Since 2018, the presence of ground waters has been regularly recorded when the level decreases. There are brackish waters with a salt content of more than 5 g/L. They typically have a high content of sodium and potassium (more than 60%) and sulfate ions (60–80%). Monitoring shows, that the shortage of fresh drinking water will increase, and as its withdrawal increases, it will accelerate in time. It will be replaced (up to 5–7‰) with mineralized ground and Black Sea water. In what proportions will be pumped (redistributed by seasons) weakly brackish (2–4 g/L) and brackish (4–8 g/L) water into water pipelines remains to be explored.