Doklady Rossijskoj akademii nauk. Nauki o Zemle

The Zabaikalian parametric borehole drilled out a metamorphic core complex on the reference geological and geophysical profile within the Central Asian fold belt, south of the Mongol-Okhotsk suture zone. In the section of the borehole drilled to a depth of 2600 m, a set of geophysical, geological and laboratory-analytical studies identified three main structural elements of metamorphic core complexes: the upper plate, detachment, and the lower plate. The upper plate (weakly metamorphosed rocks) is represented by serpentinite melange, which is separated from the underlying rocks of the lower plate by a zone of chlorite breccias (detachment). The lower plate, which is part of the crystalline basement complex, includes rocks of granite-schist and granite-plagiogneiss subcomplexes. The granite-schist subcomplex is composed of mafic and intermediate schist with amphibolites and quartzites. Biotite granite is widespread in the section; it forms layered veins with signs of synkinematic formations. According to preliminary estimates, the age of biotite granite is about 130 Ma. The schist is characterized by mylonite structure at intervals of interbedding with biotite granite veins. In accordance with data of geophysical surveys in the borehole and the petrophysical characteristics of cored rocks, the mylonite zone is the provenance of a series of inclined reflectors on the seismic reflection-CDP section, which can be traced to a depth of at least 10 km. The granite-plagiogneiss subcomplex is represented by plagiogneiss, leucogranites, and gneissic granites. In the Zabaikalian parametric borehole, a detailed section of the orshchovochny metamorphic core complex, fully characterized by core samples, of the was obtained, which should be considered as a reference for studying these structures. The investigation of this section will answer later many questions about the formation and evolution of the Central Asian fold belt.

Paleontological evidence of the presence Wordian bivalves in the Middle Permian deposits of the Omolon massif, originally described by N. Newell from the Wordian Formation of the Glass Mountains (West Texas), is presented for the first time. In the Kolymia multiformis bivalve Zone of the Bocharian Regional Horizon, pectinids of the genus Heteropecten – H. gyrtyi (Newell) and H. gryphus (Newell), were found, which allow this Zone to be confidently correlated with the Wordian Stage of the International Stratigraphic Scale (ISS) of the Permian and indicate the relationship of the Kolyma-Omolon basins with the North American basins.

Work has been carried out to assess the rare-earth potential of the main ore minerals -loparite, eudialyte and apatite of the Lovozersky and Khibinsky deposits. Super-large deposits of loparite and eudialyte are associated with the giant Lovozero intrusion (Eastern Fennoscandia, Kola Peninsula). There are a number of apatite deposits in the Khibiny complex. All these ores occupy a leading place in the structure of the raw material of Russia. The highest contents of the sum of rare earth metals are characteristic of loparite ores (the content of ΣREE in loparites is about 28 wt%), and light rare earths sharply prevail over heavy ones, the Ce/Yb ratio is about 78 000. The amount of REE in eudialites is about 2 by mass%. A remarkable feature of eudialyte ores is the high concentrations of the heavy REE group, the Ce/Yb ratio is about 14. The apatites of the Khibiny deposits occupy an intermediate position: the Ce/Yb ratio is 680, and the average concentration of the REE sum is 0.9 wt%. The conditions of formation of apatite, loparite and eudialyte ores are considered.

Composition of basalts collected from the slopes of a single seamount (guyot) located south of the eastern flank of the Charlie Gibbs FZ in the North Atlantic, was studied. High-titanium and low-titanium groups related respectively to E-MORB and T-MORB oceanic tholeites, were singled out. Basalts of the first group are characterized by higher concentrations of TiO₂, Na₂O, K₂O, P₂O₅, Fe₂O₃ and incoherent trace-elements. Basalts of both groups were melted from a mantle substrate of similar composition, which is a mixture of DM and HIMU mantle material and to a lesser extent – EM-2. Their difference in composition is due to the fact that high-titanic melts were formed deeper at a level between the spinel and garnet facies. Basalts similar in petro-geochemical and isotopic parameters were found in the axial zone of the Mid-Atlantic Ridge between the Charlie Gibbs and Maxwell FZ, where they compose large neovolcanic edifices formed with a sharp increase in the intensity of axial magmatism as a result of microplumes rise. Our studies give grounds to believe that the studied seamount was also formed as a large neovolcanic structure 64–67 million years ago under the influence of a microplume, which was branch of the Milne plume of the deep mantle.

For the large Svetlinsk gold deposit (South Urals) evidences of partial melting of minerals and possible participation of polymetallic melts in the concentration and redistribution of gold and other metals are given. Finding of bismuth and antimony minerals in ores, among which there are gold minerals new to the deposit (pampaloite, montbrayite and aurostibite), specific mineral intergrowths (polymineral Sb–Bi–Pb–Te–Ag–Au drop inclusions), enrichment of early sulphides with Low-Melting-point Chalcophile Elements (LMCE), high formation temperatures for ore assemblages (up to 400°C), as well as the occurring metamorphism of amphibolite facies indicate the possibility of the formation of such melts. Polymetallic melts at the deposit could be formed both by partial melting of early sulphides and directly from hydrothermal fluids. The signs of melting also include simplectites of calaverite and native gold in the marginal parts of the large montbrayite grain.

We present new data on manifestations of mud volcanism accompanied by gas emissions in Lake Baikal. Brittle deformations of the bottom with traces of erupted liquefied sediments were found in the Malaya Kosa Bay and the Goryachinskaya Bay in the North Baikal depression at depths of 105–163.6 m. The deposits outcropping in the extended scarps and mud craters are mainly represented by highly-porous clays. In places there are ledges of boulder-pebble sediments. The areas of the mud volcanism distribution are confined to the damage North Baikal fault zone, indicating its current activity. Disturbance of the clays and soft sediments covering them indicates the recent eruption of gas-saturated fluid and mud. At depths of 157–162 m in the Goryachinskaya Bay, cone-shaped structures ∼5 × 5 cm in size with a crater in the top part were found in them. Similar griffons were revealed in the Solontsovaya Bay along rectilinear faults opposite the paleoseismic rupture of the same name. It is necessary to continue studying the revealed shallow-water manifestations of mud volcanism and rupture deformations of the bottom by staging complex geological and geophysical studies.

The results of the analysis of focal mechanisms and the general distribution of earthquake epicenters in the Laptev Sea region were presented. For four groups of clusters of events with known focal mechanisms, the directions of the principal stress axes were calculated by the formal stress inversion method. The distributions of earthquake epicenters and crustal thickness were compared. It has been revealed that, according to seismological data, the prolongation of the extension axis of the Gakkel Ridge on the Laptev Sea shelf is currently located in the vicinity of the group of extension detachments, which is extended along the eastern boundary of the Anisin, Zarya, and Belkovsko-Svyatonossky rift chains. The older extension axis, located along the group detachments marking the eastern boundary of the Ust-Lena and Omoloy rift systems, and continuing the axis of the Gakkel Ridge, is currently much less active, realizing residual stresses near its intersection with the Khatanga-Lomonosov fault zone in the northwestern parts of the shelf and with the Lena-Taimyr zone of boundary uplifts – in the southwestern. Near the Lena delta extension axes are oriented along the Olenekskaya and Bykovskaya channels and the border of the Siberian Platform, forming the extension conditions in the eastern part and the strike-slip regime in the western part of the vicinity of the Lena delta.

Berlites of the Obnazhennaya pipe of the Kuoika kimberlite field (northeastern Siberian Platform, Olenyok uplift), a rostrum fragment of a representative of Toarcian–Early Aalenian (latest Early Jurassic–earliest Middle Jurassic) belemnites was found for the first time, namely Arcobelus cf. krimholzi (Sachs, 1970). It is shown that belemnite records previously known from here and dated to the Late Jurassic or Early Cretaceous, may be of Bajocian–Bathonian (Middle Jurassic) age. The stage of kimberlite magmatism of 177 ± 1.5 Ma, recently established in the northeastern part of the Siberian craton according to U–Pb geochronological data, falls on the time of the existence of belemnites of the genus Arcobelus. The estimated Late Bajocian–Early Bathonian age of the representative of the genus Pachyteuthis previously found in kimberlites of the Obnazhennaya pipe is consistent with the ⁴⁰Ar/³⁹Ar age (167 Ma) as well as with the age based on some paleomagnetic data (168 ± 11 Ma) reported for the pipe. In the paleogeographic schemes of the northeastern part of the Siberian Platform during the Toarcian–Early Bathonian interval, the inner part of the shelf should be extended to the territory of the Kuoika kimberlite field, taking into account the new data on belemnites.

Speleothems are unique archives of information about climate, geomagnetism, and ecological conditions of past epochs of the Earth, and over the past two decades have been successfully used for paleoclimatic and paleomagnetic studies. The uniqueness of these geological objects lies in the peculiarities of their formation and preservation in them of a wide range of geochemical, geological and geophysical proxies, and, most importantly, in the ability to obtain time series of these proxies in an unprecedentedly accurate resolution using ²³⁰Th/U, ¹⁴C and some other geochronological methods, as well as incremental chronology. This paper presents the first results of dating the Vor speleothem from the Vorontsovskaya Cave (Krasnodar region), which preserved a record of the geomagnetic excursion, obtained by ²³⁰Th/U α-spectrometry, ¹⁴C dating, and incremental chronology. Such studies have been carried out in Russia for the first time. Despite the limitations of using the methods of isotope geochronology, it was possible to obtain a limit on the age of the excursion, which probably occurred no earlier than 5500–6000 years ago. At the same time, the incremental chronology made it possible to determine with great accuracy the duration of the main phase of the excursion, which equals 871 ± 16 years, during which the virtual geomagnetic pole was in the southern hemisphere, and also to obtain the upper limit on the age of the excursion, which probably occurred no later than 5.5–6 thousand years ago.

During the passage of Typhoon Hinnamnor from September 5 to 6, 2022, typhoon-generated swell waves were discovered to arrive at the point of observation 20 hours before the typhoon itself entered the Sea of Japan. During the analysis of data obtained by laser instrument measuring fluid pressure variations, it was possible to determine the area of formation of the main group of swell waves generated by a passing typhoon, and to localize the area of generation of “forerunner” waves, as well as to describe the mechanisms of their formation and propagation.

The possibilities of detection and operational analysis of chemical elements in seawater using ultrasonic spark spectroscopy are demonstrated. The research was carried out with the help of a specially developed automated complex for spectral and hydrophysical studies, which was successfully tested for many days in expedition conditions Sea of Japan (cruise No. 81 of the R/V Professor Gagarinsky) and the Atlantic Ocean (cruise No. 52 of the R/V Academician Boris Petrov). New data have been obtained on the distribution of dissolved chemical elements and the state of seawater with high spatial resolution along long trails and at multi-day landfills in the Sea of Japan and in the Atlantic Ocean. The complex and the methods used can be recommended for in-situ studies of the state of natural water areas.

The paper presents the results of gas geochemical and lithogeochemical studies of bottom sediments in the Tatar Strait trough (Sea of Japan) based on cruise data from the R/V “Akademik M.A. Lavrentyev” (LV-81 and LV-85). Anomalies of hydrocarbon gases (HCG) and chemical elements in surface bottom sediments were determined. It has been established that sediments with anomalous methane contents are significantly enriched in Mn, Sc, V, Co, Ni, Cu, As, Se, Mo, Cd, Sb, Te, Tl, U, the concentration coefficients (K_k) of which are 1.3–5.9 times higher than their similar values at other stations. The data obtained allow us to assume the presence of gas sources of hydrocarbon migration, the continental slope and deep water area of the Tatar trough is promising for setting up detailed work on the assessment of oil and gas potential and gas hydrate content.

For the first time AMS radiocarbon dating was used to date microinclusions of organic material extracted directly from Holocene syngenetic ice wedges in the European North of Russia on the coast of the Baydarata Bay near the Yarynskaya village, 500 m south of the mouth of the Ngarka-Tambyakha River (68°51′20.27″ N, 66°52′6.51″ E). Dated ice wedges formed about 6.4, 5.0 and 1.9 ka BP. According to isotope oxygen data, the average January air paleotemperature in the Middle and Late Holocene at the coast of the Baydarata Bay was calculated. It is shown that the average January air temperature during this period here varied from about –20 to –25°C, however, during milder winters it could be about –18°C.

There is an opinion that water stability is provided by hydrophobic bonds between organic soil particles, however, there are works in which the main role in the occurrence of this property is assigned to the presence of hydrophilic organic substances in soils. The aim of the study was to clarify the nature of the bonds (hydrophilic or hydrophobic) that ensure the water stability of soils. The work used samples of sod-podzolic and gray forest soil, as well as leached chernozem. Experiments on the assessment of water stability were carried out by the method of “blades”. It is based on the dissection of linearly arranged aggregates, which were previously moistened in vacuum to values close to saturation. The energy of hydrophobic bonds depends on temperature, so the effect of temperature on the determined value of water stability was studied. Experiments have shown that with an increase in temperature, the water stability of aggregates stored in a wet state from the moment of selection increased, and with a decrease, it fell. This indicates the leading role of hydrophobic bonds in the formation of water stability. For samples dried to an air-dry state, moistened again and kept in a wet state for more than 2 weeks, no temperature dependence of water stability was found. Taking into account that the strength of hydrophobic bonds increases with increasing temperature, and hydrophilic bonds decreases, the data obtained on the immutability of water stability values can be explained if we assume the joint participation of both hydrophobic and hydrophilic bonds in the water stability of soil samples that have passed through the stage of drying to an air-dry state. In fact, these results indicate a strong change in the structural organization of soils during drying.

The article deals with modeling the dynamics of nickel concentration in soils, water and bottom sediments of lakes, caused by emissions into the atmosphere of the Pechenganickel plant (Kola Peninsula) during the entire period of its operation. The technology of balanced identification is used, which allows, based on a mathematical description of heterogeneous geochemical processes occurring in ecosystems, to combine heterogeneous experimental data and build a computer model with an optimal balance of complexity and closeness to data. The results are presented and discussed, including estimates of the retrospective state of the simulated objects (before the start of intensive studies) and a forecast of their dynamics until 2030. According to model calculations, the intensity of Ni accumulation in soil was 2.4 and 2 times higher in bottom sediments during maximum precipitation periods (1980–2005), while according to the model forecast, after the shutdown of the plant, Ni accumulation in bottom sediments will begin to decrease and Ni will slowly leach from the soil with an intensity of 0.2 mg/m2 year.

Phthalates are one of the most common pollutants, the concentrations of which in the environment in the near future, according to scientists, will only grow. High concentrations of these substances pose a serious threat to water bodies, especially for lake ecosystems, which are characterized by slow water exchange and accumulate pollutants faster, thereby reflecting anthropogenic load and environmental changes. The paper presents for the first time the results of determining the phthalate content in the bottom sediments of lakes Arangatui, Bormashovoe, Dukhovoe, Kotokel, Shchuchye. The total content of 6 phthalates varied from 51 to 2222 mkg/kg of dry weight, while the highest concentrations were noted for central stations. The distribution profile of phthalates in the bottom sediments of lakes is basically quite similar – DBP (average content of 213 mkg/kg) and DEHP (189 mkg/kg) prevailed. It is noted that the accumulation of the studied substances occurs mainly in silty sediments, which is indicated by medium and high positive correlations between phthalates, granulometric composition, the content of organic carbon and heavy metals. The high levels of individual phthalates in the sediments of the studied lakes indicate the need to study in detail the sources and distribution mechanisms in the system of “water-bottom sediments”.