Home – Home – Jornals – Russian Geology and Geophysics 2025 number 11

This paper presents new geochronological and paleomagnetic data that support the idea of later termination of magmatism in the Okhotsk-Chukotka Volcanic Belt (OCVB) within the East Chukotka flank zone than previously thought. It also allows the calculation of a new paleomagnetic pole (78.6°N, 212.2°E, A₉₅ = 4.7°, N = 104) with an age of ~72 Ma for the vicinity of the Valunistoe deposit. Combined with paleomagnetic data previously obtained by us for the Kupol deposit area, the new results lead to the following conclusions: 1) the studied areas (the Kupol and Valunistoe location) have experienced relatively small, but statistically significant, displacements relative to the North American plate during the time interval from the late Cretaceous to the present. 2) The Kupol location is rotated counterclockwise by several to a few tens of degrees relative to the North American plate, while the Valunistoe location is displaced relative to this plate in latitude by a distance of at least several hundred kilometers. 3) Based on the obtained data, we propose a model, building on the existing Bering Sea region model of Redfield and Fitzgerald [1993], according to which the Kupol and Valunistoe locations belong to the boundary area between the North American plate and the Bering plate, represented by a series of tectonic blocks. The tectonic block to which the Valunistoe location belongs is one of the westernmost blocks grouped into the Bering plate, while the Kupol location belongs to the easternmost regions of the Chukotka deformed margin of the North American plate. Deformations arising in the interaction of these tectonic blocks in the region under consideration are mainly diffuse. The Trans-Bering Seismic Belt appears to be a potential area where the discussed deformations may be most concentrated.

Results of deep seismic studies based on P- and S-wave data on a 500-km Sikhote-Alin fragment of the 8-DV reference geophysical profile are presented. Deep seismic sections of the upper crust (to depths of 15-20 km) with distributed longitudinal and transverse wave velocities are constructed. The P-wave velocity over most of the Middle Amur Basin and the East Sikhote-Alin volcanoplutonic belt varies from 4-5 km/s in the uppermost section to 5.8-6.3 km/s at depths of 7-15 km. The Sikhote-Alin orogenic belt in the section along the profile is represented by an anticlinal structure with high-velocity (up to 5.5-5.8 km/s) rocks uplifted in the center; at great depths of 10-20 km within its limits, the P-wave velocities reach 6.1-6.3 km/s. In the top of the section, the S-wave velocities within the profile as a whole are 2.7-2.9 km/s. Lower values (2.6-2.8 km/s) are observed in the center and east of the Middle Amur Depression and the eastern section of the East Sikhote-Alin volcanoplutonic belt. Higher velocities up to 3.35 km/s are observed in the central Sikhote-Alin orogenic complex. At depths of 5-15 km within the section, the S-wave velocities increase up to 3.4-3.65 km/s. The heterogeneous structure of the top of the Earth’s crust to depths of 15-20 km was identified using the P- and S-wave velocities, their ratio, and Poisson’s ratio. The profile section was used to analyze a relationship between the identified anomalies and the location of large mineragenic zones in Russian Manchuria. The correlations established earlier on the 2-DV, 3-DV, 1-SB, and East Stanovoy fragment of the 8-DV profile are confirmed using the confinement of many ore deposits to zones of lower P- and S-wave velocity ratios and Poisson’s ratio in the top of the Earth’s crust. We also substantiated the relationship between the identified surface seismic anomalies and deep (at depths of 5-20 km) roots (intermediate magmatic foci), which can be considered as ore-supplying.

Remains of calcareous cyanobacteria of the genera Garwoodia Wood, 1941, Ortonella Garwood, 1914 and Hedstroemia Rothpletz, 1913 (Garwoodiaceae family) were first identified in the late Darriwilian deposits of the Moyero River section (Eastern Siberia). Ortonella and Garwoodia were previously found on the Siberian Platform only in Silurian deposits, making this the earliest discovery of representatives of these genera in the region. Ortonella and Garwoodia dominate, whereas Hedstroemia occupy a subordinate position in stromatoporoid-cyanobacterial bioherms. Only Ortonella was found in biostromes and shell interlayers of the bivalve banks. The sediments in question accumulated in the shallow-water lagoonal environment. The latter determined the failure of skeletal metazoan organisms to become the main frame builders of biostromes and bioherms, despite the global increase in biodiversity during the Great Ordovician Biodiversification Event (GOBE). Their role was taken over by cyanobacterial communities, which proved more resistant to such environmental conditions. The increase in phosphorus content in bottom sediments apparently triggered the development of cyanobacteria; which probably caused a local paleoecological crisis of the benthic fauna in this part of the paleobasin. The latter is confirmed by the depleted ostracod assemblage in the Moyero River section (in contrast to coeval deposits of the Lena, Podkamennaya Tunguska, and Kulyumbe river sections). The decline in biodiversity of benthic fauna and, particularly, of skeletal metazoan frame builders during cyanobacterial “blooms” may be explained by the impact of cyanotoxins, which are destructive to marine life. The data obtained demonstrate that even in the age of global biotic expansion of the Ordovician period, local conditions could limit the contribution of skeletal metazoans to reef construction, maintaining the dominance of microbial communities.

A recent revision of the volume and the age of the Nemakit-Daldynian Stage of the Upper Vendian articulated its comprehensive (bio- and chemostratigraphic) characteristic. This stage includes strata ranging from the first appearance of unequivocal anabaritids (approximately 539 Ma) to the base of the Nochoroicyathus sunnaginicus Assemblage Zone of the Lower Cambrian Tommotian Stage (530 Ma). In addition to the characteristic assemblages of small shelly fossils (SSF), this stratigraphic interval is defined by specific changes in the trace fossil assembalges and by variations of carbon isotope composition in carbonates. Using the established criteria, this study evaluates the completeness of the Nemakit-Daldynian Stage in its type locality (western Anabar Uplift) and in other sections of the Siberian Platform (eastern Anabar Uplift, Olenek Uplift, Kharaulakh Uplift, Uchur-Maya Region, Patom Basin, Baikal area, Irkutsk Cis-Sayans Uplift, Biryusa Cis-Sayans Uplift, southern Yenisei Ridge, northern Yenisei Ridge, Turukhansk Uplift, Igarka Uplift, and inner regions of the Platform).

The impact facies are subdivided into coptogenic (primarily deposited) and coptomict (redeposited) units. The redeposited impact facies have been poorly studied. In this work, the deposits of the coptomict facies are characterized in detail for the first time by the example of the Kara astrobleme. The structures and textures of impactites are examined at the macrolevel, and the structural and compositional specifics of the components (lithoclasts, vitroclasts, and matrix) of lapilli and agglomerate suevites of the Sayakha River area have been described at the microlevel. The reconstruction of the past events has shown that the clastic impactites of the northwestern rim of the Kara astrobleme formed under conditions of landslide from the crater lip at the stage of the early modification of the astrobleme. The results obtained can be used to construct a model for the formation of the Kara impact structure and to improve the unified model for the formation of clastic impactites of the coptomict facies in a large meteorite crater.

The Anakit intrusion had a multistage effect on the host sediments, manifested as spurrite-merwinite metamorphism, early retrograde processes and associated formation of a uniquely diverse Cl-silicate mineralization (with a Cl content of up to 7-15 wt.%), skarn formation, and low-temperature hydrothermal processes. At the eastern contact of the Anakit massif, high-temperature spurrite-merwinite marbles were studied and characterized. The major and trace element and mineral composition of the rocks and the compositions of all rock-forming, accessory, and retrograde minerals has been determined. Under peak metamorphic conditions, the temperature in the near-contact zone (0.3-5 m) exceeded 900 °C, and X _CO2 reached 0.3. The δ¹³C-δ¹⁸O trend determined for the first time is similar to those at contacts with a minimum metasomatic influence. The small difference between the δ¹³C and δ¹⁸O values of the Anakit marbles and their protoliths (Δδ¹³C ≤ 2.0‰ and Δδ¹⁸O ≤ 4.0‰) proves the predominant contribution of metamorphic decarbonation to carbon and oxygen isotope fractionation. Along with mineral indicators, it testifies to the limited infiltration of magmatogenic fluids into the host strata.

We report the results of lithological and mineralogical studies of Holocene bottom sediments from the hypersaline Lake Bolshoe Yarovoe (salinity 150 g/L), located on the territory of the Kulunda steppe (south of Western Siberia). Research methods: X-ray diffractometry (XRD), IR spectroscopy, laser grain-size analysis, elemental analysis, and radiocarbon dating. The thickness of the uncovered sediments is 483 cm. Terrigenous minerals throughout the section are represented by quartz, plagioclase, and layered silicates (mica, chlorite, smectite, and kaolinite). The variable amounts of omnipresent authigenic minerals include halite, gypsum, carbonates, and traces of pyrite. We identified Mg-calcites with different Mg contents and aragonite using the mathematical modeling of X-ray diffraction patterns in the assemblage of carbonate minerals. The mineralogical and crystallochemical studies of sediments supplemented by the results of other analyses have provided information about the evolution of the climate of the Kulunda steppe in the Middle to Late Holocene. The comparatively arid regional climate of the Middle Holocene became more humid in the first half of the Subatlantic, but aridization signs reappeared in the section about 600 years ago (Little Ice Age).

Maxwell’s equations and the equations of two-velocity hydrodynamics of saturated porous media are consistently combined in the absence of local thermodynamic equilibrium. Equations describing relaxation of dielectric polarization vector are inferred. The law of dielectric permittivity dispersion is established in the presence of two interacting relaxation processes: relaxation of the difference in hydrodynamic velocities and relaxation of dielectric polarization. Relationship between kinetic coefficients and complex dielectric permittivity is shown, particularly relationship with hydrodynamic permeability of porous medium. A method for determining the hydrodynamic permeability of a porous medium, which does not take into account the relaxation time distribution function, based on knowledge of the dielectric spectrum was developed. Medium’s dielectric response to external inductive effect is examined for wells in saturated porous media.