Vol 521, No 2 (2025)

The first statistically significant results of U-Pb isotopic dating of dZr grains from sandstones of the Urlesh Fm., which composes a basal level of the Paleozoic succession of the Bechasyn zone of the northern slope of the Greater Caucasus, are presented. Analysis of the obtained results has shown that the accumulation time of the Urlesh Fm. is not older than the Late Tremadocian. Among the ages of dZr, the Early Neoproterozoic and older values are completely absent, so the Urlesh Fm. had not been formed on the margin of the East European Platform (Baltica). The presence of a bright Peri-Gondwana provenance signal in the sandstones of the Urleshs Fm. allows us to consider it and the underlying formations of the Khasaut metamorphic complex as a fragment of the Kadom-Avalonian margin of Gondwana.

Sviatonossites (andradite-bearing syenites) were discovered on the Sviatoy Noss Peninsula (Transbaikalia) in the early 20th century. One of the debatable issues is their age, which is not reliably established by isotope methods. Accessory zircon U-Pb isotopic data from sviatonossites and leucosyenite showed a late Paleozoic age for the Markov (310-297 Ma) and Eskola (317-312 Ma) massifs of the Sviatoy Noss Peninsula, synchronous with the formation of granitoids of the Barguzin complex (330-290 Ma). Zircons from leucosyenite of the Markov massif have a typical magmatic structure, which is consistent with the Th/U ratio > 0.3. Anhedral zircons from sviatonossites in combination with the lower Th/U ratio < 0.1 indicate recrystallization processes at the formation stage of the Markov and Eskola massifs. The older ⁴⁰Ar/³⁹Ar isotopic ages for amphibole from the Markov massif sviatonossite  (360-336 Ma) are associated with the presence of excess ⁴⁰Ar, the source of which could be Early Paleozoic metamorphic rocks.

Macroscopic fossils as composite molds and casts of Ediacara-type soft-bodied organisms were found in the Katchergat Formation of the Upper Precambrian Baikal Group of the Western Cisbaikalia for the first time. Among them, species of Palaeopascichnus delicatus and P. linearis of the group palaeopascichnida, and Arumberia-type microbially induced sedimentary structures were identified. This discovery significantly clarifies the age limits of the deposition of the Katchergat Formation, the stratigraphic position of which in the Upper Precambrian section of Western Cisbaikalia was controversial

Gold-bearing large quartz veins occur in Neoproterozoic metasedimentary hosted rocks of the Bolshoi Karatau. The Karatau ridge is a northwestern part of the Tien Shan Range, southern Kazakstan.  The oldest Neoproterozoic sedimentary rocks are exposed in the axial structural-formation zone, which is confined by the Main Karatau Fault. Native gold was characterized for the first time for this region. The fineness of native gold is 858–956‰. Native gold from quartz veins contains inclusions of bismuth minerals. The low-sulfide quartz gold type mineralization in quartz veins genetically associated with the small granite intrusions and was referred to intrusion-related gold systems. This conclusion based on geological settings of the area, internal structure of native gold and Bi-Te-Cu-Pb-S association of mineral inclusions in native gold grains.

The value of the scattering intensity in the dynamic light scattering (DLS) method is proportional to the mass concentration of polymethylmethacrylate (PMMA) particles in water suspensions containing 1-100 mg/l of particles with a size of 0.08-2.0 μm determined gravimetrically, confirms this possibility. A significant correlation between the intensity of scattering of DLS in filtrates and the concentration of chemical elements Fe, Al, Ti, Th, and REEs in them, which are prone to migration in the coarse colloidal forms, is another proof of the dependence of the intensity of DRS filtrates on the content of large colloids in them. This makes it possible to characterize the initial concentration of large colloids and their losses during the clogging of filters, as well as to assess the role of large colloids in the balance of chemical elements in river waters.

In the northern part of the Rybinsk-Panimbinsk volcanic belt, the first Rb-Sr and 147Sm-143Nd results on early Mesoproterozoic rift picrite- picrobasalt volcanism and metamorphism were obtained. Petrogeochemical data indicate the sedimentary-terrigenous nature of most of the samples of the Mikhailovsky site taken from the section of the Kordinsky formation. The presence of a noticeable admixture of basitic matter in them in the form of tuffs or washed volcanomictic material is confirmed by an increased content of MgO and CaO, reduced REE, Zr, Hf and Nb. The results of geothermobarometry and analysis of the metamorphism features of volcanogenic-sedimentary rocks of the reference sites show the heterogeneous nature of the initial rock transformation conditions: 4.8-4.9 kbar/527-549°C - picrobasalt metatuffites; 5.0–5.8 kbar/543-612°C – metabasites; 3.5-4.6 kbar/522-636°C – metapelites. The established age of riftogenic picrite-picrobasalt volcanism and related somewhat late metamorphism processes in the Precambrian of the central part of the Yenisei Ridge correlates with the time of formation of plagiogranites of the Nemtikhinsky complex and with the reference Mashak plume magmatism in the South. In the Urals, manifested in the geodynamic environment of stretching during the collapse of the supercontinent Nuna.

A new approach to obtaining U-Th-He thermochronologic information is proposed. The content and mobility of radiogenic helium in concentrates of pyrite, magnetite, hematite and amphibole from albitites and their host rocks from gold-bearing uranium ore occurrences in the Salla-Kuolayarvi belt (northern Karelia) were estimated based on the results of incremental heating of samples with simultaneous registration of helium flux. The values of apparent U-Th-He ages were calculated taking into account the contribution of the trapped component. Suitability of the mineral species for placing the age boundaries on the evolution of ore-bearing metasomatic rocks was considered on the basis of the calculated parameters of helium mobility in the lattice, as well as petrographic features of each individual sample

A mathematical model has been formulated for the degradation of saline permafrost rocks (MMP) containing ice, accumulations of metastable self-conserved gas hydrates and free gas due to climate warming and the influence of heat flow from below. In the simplest case, an analytical expression of the laws of reservoir degradation is obtained from the model from above due to an increase in temperature at the upper boundary, and from below due to the inclusion of an increased heat flow. It is shown that degradation from below occurs mainly according to a linear law in time, while degradation from above occurs more slowly, i.e. only according to the root law. The proposed model and the obtained simplest formulas can be used to study the degradation fronts of a frozen formation not only due to ice melting, but also earlier and faster decomposition fronts of metastable gas hydrates without ice melting. The corresponding thermodynamic points are close. As an application of the model, a specific numerical variant is considered and the curves of the degradation fronts are illustrated

An unprecedented increase in postseismic activity at the Punggye-ri test site,  DPRK, has been recorded by the International Monitoring System (IMS) stations over the past year and a half. The main parameters of the aftershock emission differ significantly from the well-known estimates made previously after numerous underground explosions in various seismotectonic settings. Essentially, a continuous sequence of seismic events after the sixth announced explosion in 2017 has been observed for more than 7 years. Since the second half of 2023, an increase in the frequency of seismic events has been recorded. Both observed processes are not consistent with the well-known Omori law. The number of events with relatively high magnitudes is increasing. The uniqueness of the aftershock sequence requires high sensitivity of the registration system and resolution of signal detection methods, as well as the accuracy of the source parameters for further study of the nature and mechanisms of postseismic activity.

New data on the composition and concentrations of hydrocarbon gases in the upper horizons of bottom sediments of Avacha Bay and the adjacent sector of the Pacific Ocean are presented. The established concentrations of methane and the sums of its homologues are characterized by high variability – 0.0003–120.9385 and 0.00005–0.00753 cm³/kg and the formation of gas anomalies in the sediments of the shallow shelf (Avacha Bay, Russkaya Bay, Vilyuchinskaya Bay and Listvennichnaya Bay), the outer shelf and the continental slope at sea depths and sampling of 14–800 m and 3–50 cm. The data on the isotopic composition of carbon δ¹³C-CH₄ from -78.1 to -33.4‰ and δ¹³C-CO₂ from -19.8 to -11.1‰ indicate the formation of natural gases of various polygenetic (mixed) genesis in the bottom sediments of the region and, with a high degree of probability, their significant influx from the underlying sediments.

This paper presents the results of the generalization and scientific analysis of gas-geochemical studies of hydrocarbon gases in the bottom sediments of the East Arctic shelf. As a result of the studies, methane and the sum of its homologues were found in the sediments of the region in concentrations of 0.0010–12.1502 and 0.000002–0.03626 cm³/kg. In general, the distribution of hydrocarbon gases in the bottom sediments is characterized by significant variability and the formation of local, linear and areal hydrocarbon anomalies. This fact is explained by the presence of underlying gas-saturated sources, tectonic conditions, seismic activity, geostructural position, sediment depth and the influence of other geological factors. Based on the generalization and analysis of the author's data, a map of the distribution of hydrocarbon gases in the bottom sediments of the central part of the East Arctic shelf was compiled for the first time.

The article presents a strategy for predictive empirical-statistical modeling of forest ecosystems as objects of terrestrial geosystem monitoring. Local mechanisms of global changes are revealed through an empirically established display of the background bioclimatic trend by a catenary system of biogeocoenoses. Regional structures of localized natural zonality capable of simulating the main directions and scales of geo(eco-)system restructurings are considered. Landscape-ecological forecast is described as a system of operations with ecological (hydrothermal) niches of the objects under study. Empirical imitation of forecasts is implemented as a reproduction of predicted scenarios of biogeocoenotic systems according to the laws of their basic spatial organization, with the replacement of spatial coordinates with time coordinates in the forecast procedure, in accordance with the fundamental properties of ergodicity of the natural environment.