Home – Home – Jornals – Russian Geology and Geophysics 2025 number 2

Porphyritic amphibole-plagioclase andesites at the southern margin of the Utanak ultramafic massif (Stanovoi superterrane, Russian Far East) show low yttrium and ytterbium contents and high Sr/Y and La/Yb ratios typical of adakites. Microinclusions in these volcanic rocks are Cu-Ag-Au alloys, native silver, composites of gold and silver with Cu, Zn, In, Mn, Ni, and Mo minerals, as well as microparticles of platinum, silver sulfides and chlorides, pyrrothite, chalcopyrite, barite, tungsten oxide, crocoite, and cassiterite. The structural features of some microinclusions and their association with primary amphibole and plagioclase suggest their magmatic origin, while other microinclusions hosted in the quartz-chlorite- K-feldspar groundmass formed during later metasomatism. The Utanak adakites are characterized by elevated gold contents (up to 134 ppb) and, together with other manifestations of Mesozoic adakitic magmatism within the Stanovoi superterrane (Il’deus, Lucha, and Gabbrovyi massifs), are classified as ore-bearing (fertile) adakites according to geochemical criteria. We suggest that common association of adakitic magmatism with large porphyry, epithermal, and skarn deposits at convergent plate boundaries is related not only to the high water content and the oxidation state of adakitic magmas but also to the initial enrichment of the latter in various ore components.

The Russian sector of the Eastern Arctic is characterized by large basins with thick sedimentary filling, primarily on the shelf and continental slope of the seas of the Arctic Ocean. A number of geological, geophysical, and geochemical features point to a hydrocarbon potential. At the same time, the age and composition of the sedimentary infill of the shelf basins have been controversial until now due to the lack of wells drilled in the shelf area. Six stratigraphic wells were drilled with core sampling in the eastern Laptev Sea (Anisin-Novosibirsk block owned by Rosneft) with a depth of 100 to 199.5 m during the Rosneft Stratigraphic Drilling in Arctic (RoSDAr) project in 2021. The results of complex biostratigraphic studies of the core show that the oldest strata in the well sections are Upper Barremian - Lower Aptian deformed silty mudstones (folded basement assemblage) overlain with angular unconformity by sands, silts, and clays of the Paleocene. The wells also penetrate the Eocene, Oligocene, and Miocene-Quaternary clastic rocks. A comprehensive analysis of stratigraphic drilling and seismic data refines the geological models of the region and provides better understanding of its hydrocarbon potential. The data show that Cenozoic strata play a more significant role in the sedimentary cover of the Laptev Sea than was previously assumed.

This study contributes to the development of C, O, and Sr isotope chemostratigraphy of the upper Berriasian-Valanginian of Arctic Siberia and to the improvement of the Boreal-Tethyan correlation scheme based on it. Results of an isotope-geochemical study of belemnite carbonate material from the Anabar and Boyarka river sections and the Nordvik Peninsula section (Ryazanian-lower Hauterivian) are presented. The following three phases of the global Weissert event are identified: a rapid increase in δ¹³C at the turn of the early and late Valanginian, stabilization of δ¹³C in the late Valanginian, and a smooth decrease in δ¹³C since the end of the Valanginian to the earliest Hauterivian. It is suggested by the δ¹⁸О data from the Neocomian formations of Siberia that the climate cooling associated with the Weissert event is negligible. The resulting ⁸⁷Sr/⁸⁶Sr values for the Boyarka and Nordvik sections in combination with bio- and magnetostratigraphy indicate that the base of the upper Berriasian falls into the middle part of the Hectoroceras kochi ammonite Zone of the Ryazanian Stage. It is revealed that the top of the Ryazanian is located below the base of the Valanginian. The interval between these boundaries in Siberia corresponds to the lowermost part of the Neotollia klimovskiensis ammonite Zone. The age of the ammonite zones of the Boreal (Siberian) standard of the lower Valanginian is clarified. It is reliably determined that the Homolsomites bojarkensis ammonite Zone belongs to the lower Hauterivian rather than upper Valanginian, which resolves the issue that has been the subject of lengthy discussions.

The article discusses modern methods of quantitative assessment of the elements of hydrocarbon resource structure in large oil and gas (petroleum) basins. The assessment is based on the law of mass distribution of hydrocarbon accumulations, i.e., the truncated Pareto distribution. The procedure developed is used for: estimation of the truncated Pareto distribution parameters and cumulative hydrocarbon volumes concentrated in pools, prediction of their number and size distribution and total resources within each size-class interval; simulation of spatial distributions of hydrocarbon accumulations with transformation of a population of HC pools into a population of fields; prediction of the number and size-class distribution of total HC resources in pools and fields, and fields distribution by the number of HC pools. The involved analytical approach based on the simulation mathematical modeling is described.

Oil and bitumen shows with previously unknown hydrocarbon biomarkers - 9-methyl, 8-14-secohopanes - were encountered in the sections of hydrogeological wells on the northeastern slope of the Aldan anteclise. Shows of biodegraded asphaltites are confined to the cavernous horizon in the middle Cambrian limestones of the Tankhai Formation. The relatively high residual concentrations of the “new” biomarkers are due to their very high resistance to biologic oxidation processes. Geologic materials and geochemical data on the studied naphthides suggest that in the region under consideration there is a typical oil deposit sealed in the “head” of the cavernous horizon by highly viscous bitumens.

This paper presents the results of constructing a model of the geoelectric structure of Northern Vietnam obtained by 3D inversion of magnetovariational tippers calculated for 13 values of variation periods in a range of 40-10047 s at 12 points where geomagnetic variations are recorded. Inversion is performed using the ModEM software, which makes it possible to construct a model in a 400 × 400 × 200-km spatial region with the center at the Hanoi Observatory (PHU). The resulting model of the geoelectric structure contains two regional blocks separated by the Red River fault region. A conductive block is located in the southwest of the fault region, and a high-resistivity block is located in the northeast. The boundary of the blocks, inclined to the northeast at an angle of about 45°, is visible to a depth of 150 km. The conductive block occupies the region between the Red River and Song Ma faults. Its western boundary could not be localized due to insufficient data in this region. Highly conductive local blocks stand out against the background of the regional conductive block. They usually gravitate toward the faults and are located in a depth range of 10-20 km with a slight inclination to the west on latitudinal profiles and to the south on meridional ones. In a depth range of 12-14 km, they merge into one highly conductive band extending in the northwest and marking the Red River fault system connected to the Gulf of Tonkin waters. Also, there are more massive highly conductive blocks in depth intervals of 20-50 km, which are often associated with upper crustal ones. There is a highly conductive block observed on the latitudinal profile, passing through the central region of the Hanoi Basin, and steeply dipping to the east (75°) to depths of more than 100 km. The deep geoelectric features of the Red River fault system are compared with the geoelectric section under their continuation in Southern Tibet in the adjacent territory in China.

The article presents a practical approach to the geological and geophysical spatial data collection and preliminary processing to use in machine learning models for geophysical applications. According to the established principles for estimating efforts in data analysis, which are confirmed by the results of surveys among specialists, this stage is viewed as major time and resource-consuming, amounting up to 80% in total volume of data analysis for a hypothesis testing project. The paper focuses on creating a consistent data set that integrates geological and geophysical information on a given region. We consider problems of different sources in the geodata representation to be related to their format (vector/raster), scale, type of attribute information (quantitative/qualitative) and their availability. The algorithm formalization and synthesis for combining geospatial data and converting them into quantitative vectors is a critical aspect. Combining various data draws on the concept of neighborhood fitting in with the data selection techniques and data consolidation strategy. The paper presents the general architecture of the software and hardware complex which includes a module for data collection and transformation in Python using the Pandas library, a data storage system based on the PostgreSQL DBMS (Database Management System) with the PostGIS extension. It is shown that for the considered class of problems in geophysics, it is sufficient to use a relational DBMS for data storing and processing. If the problem dimension increases, it is proposed to use the Big Data technology based on Apache Hadoop for scaling the system. A practical application of the proposed approach is demonstrated as results of data collection for the Caucasus region and eastern sector of the Russian Arctic. Based on the prepared data, experiments were carried out using machine learning models for recognition of locations of potential strong earthquakes and for sensitivity estimation of several geophysical features of these regions. The article presents the experimental results and evaluation of their efficiency.

Records obtained at seismological stations contain information not only about earthquakes, explosions, but also from various other sources of seismic waves. The sources of such waves can be various buildings and structures that vibrate with their own frequencies. Seismologists can understand the registered wave field, identify the waves from these sources and characterize them. It is possible to implement seismic methods of remote control over changes in the technical condition of various objects. Contemporary hydraulic structures were built a long time ago and aging processes in them lead to destruction of materials and formation of cracks, so these objects require continuous monitoring of their condition. The aim of this work is to investigate the possibility of determining the occurrence of cracks in the body of the dam of the Sayano-Shushenskaya hydroelectric power plant by analyzing its natural frequencies depending on the filling and drawdown of the reservoir. For this purpose, we placed a seismic station several kilometers away from the object of study. With the help of this station, as well as with the help of the seismological data obtained at the seismic station “Cheremushki”, located 4.5 km from the HPP, for 20 years, works were carried out to study the possibility of determining the natural frequencies of the dam with high accuracy when they change in time. The possibility of controlling the physical parameters of structures and operation of various units of the HPP for a long period of time was demonstrated. Examples of determination of frequencies of high- and low-quality signals are considered.

Teleseismic receiver functions (RF) were extracted from data collected at eight short-period, three-component seismic recording stations over the Guelma-Constantine Basin, northeastern Algeria, to improve the understanding of crustal structure and geodynamic processes. The H -κ stacking method was used to determine the Moho depths and average v_P/v_S ratios at each station. Careful linear inversion of RF was performed to determine the most appropriate average shear-wave and P -wave velocity profiles at each site. Both methods have yielded highly congruent results, with Moho depths showing robust correlations with previous seismological and geophysical studies. The previously observed pattern of the increasing Moho depth from north to south in the Tell Atlas has been confirmed. Furthermore, the identified transitional nature of the Moho in the Constantine Basin is consistent with a recent study. In addition, we identify a low-velocity zone (LVZ) at approximately 20 km depth within the southern Guelma Basin, confirming previous results in the Constantine Basin and suggesting an eastward elongation of the LVZ, at least into the southern periphery of the Guelma Basin. Examination of data from the northern tip of the Hammam Debbagh-Roknia NW-SE fault, the western boundary of the Guelma pull-apart basin, revealed a shallow Moho depth (22 km), less than the basin average depth of 25 km. The LVZ observed in the lower crust (12 km) suggests the presence of partial melts, consistent with gravimetric and chemical analyses of hydrothermal sources in the area. The extensional tectonic activity along this boundary, coupled with the low-viscosity zone and low average v_P/v_S ratio, is potentially associated with delamination processes. The effectiveness of our approach underscores its potential as a viable alternative or complementary method for investigating variations in the Moho depth.