Home – Home – Jornals – Russian Geology and Geophysics 2025 number 9

Nemakit-Daldynian Stage was originally introduced as a regional stage, embracing the lowermost Cambrian strata with the oldest small shelly fossils, for the Anabar uplift sections in the 1960s. In subsequent years, it became widespread in the works of Soviet researchers as the terminal stage of the Upper Vendian series. Almost at the same time, the concept of the Manykaian stage appeared, which is close in its volume and geological meaning to the Nemakit-Daldynian Stage. Although this unit plays a crucial role for our understanding of the chronology of biotic turnovers at the Vendian-Cambrian transition, its status, age, and correlation with the Manykaian stage and units of the International Chronostratigraphic Chart (ICC) remain unclear. This study reveals the development of concepts regarding the stratigraphic volume and rank of the Nemakit-Daldynian Stage. The integrated biostratigraphic, stable isotope and geochronological data shows this unit belongs to the Upper Vendian series and spans the interval from the first appearance of unequivocal anabaritids (~539 Ma) to the first appearance of the Tommotian small shelly fossils (~530 Ma). In this interpretation, the Nemakit-Daldynian Stage corresponds to the Fortunian stage of the Cambrian System in the ICC. The base of this unit is coeval to the base of the Rovno regional stage of Baltica.

Results of an analysis of the geographical distribution and taxonomic diversity of dinoflagellate cysts in the Campanian age of the Northern Hemisphere are presented. Three types of dinocyst assemblages are established on the basis of the qualitative and quantitative assessment of their generic composition. Some stratigraphically important genera and species, previously having narrower habitats, have been widely distributed due to transgressive events, expansion of interbasin connections, and the presence of multidirectional meridional currents. This study reveals the possibility of comparing the North Siberian dinocyst assemblages with those from the stratotypes containing the orthostratigraphic faunal groups of the West European and North American Campanian deposits through the ecotone sections of the Subpolar Cis-Urals and the south of Western Siberia.

A continuous record of paleogeographic events of the Holocene has been reconstructed based on biostratigraphic study and radiocarbon dating of the coastal peat bog in Nerpichy Bay, the Sea of Okhotsk. Development of zonal landscapes since the end of the late Pleistocene began from shrub forest-tundra to birch elfin forest with the first appearance of broadleaved trees in the early Holocene (about 10 cal ka BP), dominance of dark coniferous taiga with maximum participation of broadleaved trees in the middle Holocene, their further decrease in the late Holocene and almost complete disappearance at present. On the coast peat began to accumulate when temperature increased, about 10.2 cal ka BP. A rapid change of the swampy larch forest, after large-scale fires, to a community dominated by true mosses, and then to subshrub-grass-sphagnum phytocenoses was a peculiar feature of the bog ecosystem evolution. Further successions occurred with a gradual replacement of eutrophic-mesotrophic sphagnum mosses by oligotrophic Sphagnum fuscum ; for the latter the highest rates of peat accumulation were noted to be at 7.2-6.1 cal ka BP. At that time the average annual temperature was approximately 2 °C higher than the present, and the long-term average annual precipitation was approximately 40 mm higher than at present. The most pronounced cooling periods in the Holocene occurred at 10.6-10.2, 9.2-8.9, 8.3-8.0, 5.2-4.8, 4.3-4.0, 3.5-3.3, 2.8-2.5, 1.5-1.0 and 0.6-0.4 cal ka BP. The cooling events identified in the southwestern coast of the Sea of Okhotsk are consistent with the sequence of cold events of the Holocene both in the region and in the Northern Hemisphere.

We analyzed the mineral and chemical compositions of water and bottom sediments of lakes as well as the isotopic compositions of carbon and oxygen in dissolved and precipitated carbonates and of elemental, sulfate, and hydrogen sulfide sulfur. It has been established that the groundwater and surface waters feeding saline sulfate lakes belong to the sulfate-hydrocarbonate or hydrocarbonate-sulfate types with pH < 9 The research shows predominantly soda and sulfate lakes in the study region. It has been revealed that the sulfate coefficient of the water in such lakes exceeds 1 and that it decreases with increasing salinity as a result of the precipitation of thenardite and sulfate reduction. Changes in the hydrochemical types of lakes lead to changes in the mineral composition of their bottom sediments. During low-water periods, autochthonous sedimentation prevails, and the portions of dolomite and clay minerals increase: in sulfate lakes, kaolinite and hydromica accumulate; in soda lakes, montmorillonite is additionally prominent. Concurrently, heavy oxygen isotope accumulates in carbonates. Further increase in water salinity is accompanied by the precipitation of gaylussite, trona, and anhydrite and by the ware transition from soda to sulfate types. The formation of thenardite changes the lake water from the sulfate to the chloride type. During the period of lake desalinization, allochthonous sedimentogenesis prevails, leading to the accumulation of clastic material in lacustrine sediments, primarily plagioclases and feldspars; in addition, carbonates with an isotopically lighter composition of oxygen accumulate.

The present study is aimed at the determination of organic compounds in thermal waters of the Belokurikha deposit (Altai Territory), which is important both for balneology and for regional ecology. The TOC concentration ranges from 0.42 to 0.55 mg/L. Using capillary gas chromatography-mass spectrometry and solid phase extraction, 69 organic compounds were identified, which form 16 homologous series. Normal and isoalkanes (25%), carboxylic acids and their esters (24%), and aromatic hydrocarbons (14%) are predominant in the thermal waters. The molecular-weight distribution of normal hydrocarbons (the odd/even ratio is 1.3-1.5, ACL = 16.6-17.5) and the presence of characteristic compounds indicate that the organic matter in the studied waters is of autochthonous, predominantly bacterial origin. Some of the identified components suggest a low degree of technogenic pollution of the waters (phthalates and compounds containing a tert-butyl group and chlorine). Oxygen-bearing compounds might exert a therapeutic effect on the human body. Comparison of the studied thermal waters with Far Eastern hot springs showed both a great similarity in the distribution of organic compounds and a difference because of the contribution of plant detritus to the formation of the organic component of Far Eastern thermal waters.

The article considers the issues of determining the characteristics of target horizons using methods capable of learning on large volumes of heterogeneous data and high prediction accuracy. The methods are used to solve problems of seismic facies analysis at oil and gas fields, the main purpose of which is to reconstruct the sedimentatry rocks and predict lithofacies in the study area. The object of the study was one of the fields in the Volga-Ural region. An improved Bayesian classifier was used as a tool. It was used to determine promising distribution zones of the productive B₂ formation reservoir of the Bobrikovian deposits of the Lower Carboniferous and to assess the hydrocarbon production potential. During the research, the effectiveness of the application of machine learning methods and the proposed improvements was analyzed.

Uniaxially compressed granite samples were subjected to pointed impact damage directed orthogonally to the compression. Generation of the impact-induced acoustic emission (AE) was recorded by a wide-band piezoelectric transducer made of high-sensitivity PZT ceramics. The AE time series were analyzed in the frequency ranges of 80-200 kHz (conventionally low-frequency range) and 300-500 kHz (high-frequency range). Energy distributions in AE time scans recorded in the lower frequency range follow the power law, which is characteristic of the cumulative process of microcrack formation, whereas distributions recorded in the high-frequency range are described by an exponential (Poisson-like) function characteristic of random, non-interacting AE-events. Concentration of microcracks in the low-frequency range was characterized by the Gutenberg-Richter b -value. At continuous impact energy, the b -value increased progressively with increasing uniaxial compression applied to the samples from zero to the highest subcritical value, which suggests lowered contribution of larger cracks. As the compression load approached (but without reaching) the ultimate strength, the impact-induced subthreshold macrofracture of the granite sample (trigger effect) occurred.

The paper describes the problem of distortion of stacking velocities estimated from CDP gathers caused by statics applied for compensation of the effect of near-surface (NSS) velocity anomalies. An analytical solution of the problem of stacking velocities correction for statics applied for NSS and deep velocity anomalies is presented. The results of numerical modeling demonstrate the high performance of the proposed solution. A comparative assessment of the accuracy of structural imaging with the proposed methodology and the option without velocity correction and other algorithms for solving the problem is provided.