Doklady Rossijskoj akademii nauk. Nauki o Zemle

The composition of metadiabase dykes, metabasalt lavas and plagiogranite veins of ophiolite association in the upper reaches of the Koiard River of the Kurtushiba Ridge has been studied. The results of geochemical studies show that these ophiolites are characterized by N-MORB+IAB–like composition. The U-Pb age of the ophiolites is 569±6 Ma. The ophiolites of the Kurtushiba Ridge, along with the ophiolites of the Shatsky massif in Western Tuva and the island-arc complexes of the Ondum subzone, were formed simultaneously or close in time, ~578–569 Ma, at the early stage of evolution of the Tannuola-Khamsara paleo-island arc.

The rocks of the Ilin-Tass anticlinorium overlie the folded structures of the Moma Range and extend from the headwaters of the Kolyma River in the northwestern direction to the Indigirka River basin. The paper presents the first data on U–Pb dating of detrital zircons of volcanogenic- terrigenous rocks of the Bastakh series. It was found that the provenance for the rocks of the Bastakh series was located along the entire periphery from the area of accumulation of volcanogenic-sedimentary formations. It is shown that the age of the three lower formations of the Bastakh series, which was previously considered to be Tithonian, covers the Neocomian and is accepted as Tithonian-Barremian.

Geological and structural observations carried out within the Marinskoye gold deposit of the Allakh-Yun zone of the Okhotsk-Koryak belt showed the occurrence of several deformation events and associated early and late orogenic mineralization during the Late Jurassic – Aptian subduction. The Late Jurassic stage D1 is characterized by structures of plastic deformations, green-schist metamorphism and early orogenic gold mineralization. The structures of the second deformation stage D2 (folds of shale cleavage, crenulation cleavage) are developed locally. Fragile ore-controlling structures of the third stage D3 are superimposed on plastic deformations after their exhumation. The obtained dating of 119.4±4.7 million years (⁴⁰Ar/³⁹Ar, sericite) of late orogenic gold mineralization is close to the estimates of age of large granitoid massifs with crust-mantle sources of the Allakh-Yun zone. The Late orogenic Marinskoye gold deposit was formed under conditions of compression and western transport of rocks during a change in the tectonic setting on the eastern active continental margin of the Siberian craton, related to the change in plate dynamics in the northern part of the Paleopacific at the beginning of the Aptian century.

Granitoids associated with quartz vein mineralization of the gold-sulfide-telluride type in the Middle Urals were dated for the first time. The object of the study is albitized granites-porphyry of the Byngy stock. The quartz veins and near-ore metasomatites of the berezite-listvenite formation of the eponymous deposit are confined to the endo- and exocontact zones of this stock. Both native gold and tellurides of Au, Ag, Bi, Hg, Cu and other metals are widely distributed in quartz veins. The age of the least modified rocks of the Byngy stock is 394.7±3.1 million years (the end of the Emsian age of the Early Devonian) was determined by the U–Pb-method for zircon grains (SHRIMP-II, VSEGEI Isotope Research Center). The data obtained indicate that the formation of granites of the Byngy stock, as well as comagmatic host volcanites with it, was associated with the Devonian stage of island-arc magmatism, which took place on the territory of the eastern sector of the Middle Urals from the second half of the Emsian to the middle of the Frasnian age. In terms of time and geodynamic conditions of formation, quartz vein mineralization of the gold-sulfide-telluride type differs from gold-bearing quartz veins of the gold-sulfide type, for which telluride forms of metals are not characteristic. According to available data the formation of the last type of mineralization in the Middle Urals occurred from 315 to 300 million years ago, which corresponds to early episodes of collisional magmatism. The increased concentrations of tellurium in postmagmatic ore-bearing fluids generated in island-arc geodynamic conditions are most likely due to the conjugation of the generation of granitoid and co-aged melts of the basic composition with increased tellurium contents.

The results of the study of chloroform bitumen (CB), organic carbon (C_org), aliphatic (ACHs) and polycyclic aromatic hydrocarbons (PAHs) in the bottom sediments of the Kolyma estuary showed that the sediments of the pier for small vessels in the village of Chersky, as well as in the port of Zeleny Mys, are the most polluted with oil products (according to IR spectra, composition of alkanes and PAHs). In 2018, the concentrations varied in the range: AHCs – 35–318 μg/g, PAH – 37–970 ng/g, weathered petroleum hydrocarbons dominated in the alkanes. In the sediments of the river itself and the Ambarchik Bay of the East Siberian Sea, the hydrocarbon concentrations were significantly lower: AHCs 71–25 μg/g, and PAHs – 28–100 ng/g), and terrigenous compounds of natural origin prevailed in their composition, and the Kolyma marginal filter copes with incoming pollutants. In subsequent years, the concentrations of hydrocarbons in port waters changed depending on the emissions of petroleum products.

We present new data on the geology, geochemistry the age of alkaline magmatism in the South-West Khovsgol region. U–Pb (ID–TIMS) geochronological studies on titanite from the alkaline clinopyroxenite of the Shivleggol massif (part of the Beltesingol group of massifs) reveal an age estimate of 450±1 million years. This new age enables us to identify another stage of polychronous Early Paleozoic alkaline magmatism within the Tuva-Mongolian massif.

A new type of Pt-Pd mineralization has been established in the chrome ores of the Main Saranovskoye deposit. The palladium content in the studied chromitites reaches 7.7 ppm, platinum – 0.5 ppm. The minerals are represented by tellurides, arsenides and arsenido-antimonides Pt and Pd – kotulskite, temagamite, atheneite, sperrilite, isomertiite. Chromitites have a specific spotted structure and occur in the form of lenticular separations among the massive medium- and high grade ores of the eastern and western ore bodies of the deposit. As in other stratiform complexes, the formation of Pt-Pd mineralization is associated with the crystallization of residual melt, which penetrated into already crystallized chrome ores. The structural and textural features of chromitites suggest that the localization of platinum-palladium mineralization occurred under the influence of tectonic processes.

Most researchers associate the formation of large sedimentary basins on the continents with strong stretching of the lithospheric layer – rifting. The formation of the world's largest West Siberian basin is explained by post-rift subsidence of the crust after rifting at the Permian-Triassic transition. Post-rift subsidence is commonly described using the classical pure shear model. Analysis of seismic profiles with a total length of 2.500 km showed that this model is not applicable to the West Siberian basin. The rate of post-rift subsidence of the crust should decrease rapidle and smoothly over time. In the West Siberian Basin, the most rapid subsidence occurred, however, not in the Triassic, immediately after the supposed stretching, but in the Jurassic and Cretaceous, when the post-rift subsidence should have been practically completed. Moreover, in the Mesozoic and Cenozoic, the subsidence of the crust was very complex, and it was highly heterogeneous both in time and area. Far from the active boundaries between the plates, such a subsidence with the accumulation of up to 6–7 km of sediments could only be caused by significant contraction of rocks in the Earth's crust as a result of prograde metamorphism, catalyzed by the influx of surface-active fluids from the mantle into the crust. The strong heterogeneity of the subsidence indicates that the influx of these fluids into the crust was also heterogeneous in time, space, and possibly composition.

The described fragment of a pterosaur humerus (presumably from the Upper Jurassic deposits of the Volga Region) is one of the first finds of the Pterosauria in Russia. The humerus is characterized by a weak S-shaped curvature of the shaft, a distally tapering triangular deltopectoral crest, and a pneumatic foramen on the posterior side of the shaft. In terms of the shape of the deltopectoral ridge, this specimen is most similar to the humerus of the gallodactylid Cycnorhamphus suevicus (Quenstedt, 1855) from the Upper Jurassic of Western Europe. This feature, as well as the presence of a pneumatic foramen, allows us to attribute the studied form to Pterodactyloidea.

The third finding of ikaite in Holocene sediments of the Chukchi Sea is described. Based on the results of a comprehensive study (mineral, chemical, isotopic composition), a conclusion was made about the formation under low temperatures with the participation of carbon from the oxidation of organic matter and methane.

The rapid reduction of the Arctic Sea ice area in recent decades and the increase in the duration of ice-free navigation along the Northern Sea Route is one of the positive consequences of the global warming for Russia. At the same time, further retreat of the sea ice may lead to a prolonged seasonal open water period outside the Russian exclusive economic zone (REEZ) with significant economic and geopolitical risks. The paper provides estimates of possible changes of the sea ice concentration in the Arctic and the duration of open water period, including outside of REEZ in the 21st century, based on the CMIP6 climate model ensemble for moderate and aggressive scenarios of anthropogenic forcing. In particular, it is shown that already by the middle of the 21st century, the duration of ice-free navigation outside REEZ may exceed two and a half months.

The regionalization of Russian forest landscapes for spatial extrapolation of greenhouse gas fluxes at regional and national scales was performed. Using the method of simple linear iterative clustering based on 12 variables, the study area was divided into 78 ecoregions. The spatial data on climatic characteristics, surface topography, soil cover and vegetation were collected from open sources and resampled to a grid of 0.0025° × 0.0025°. The results of the clustering were compared with expert-defined geobotanical and physical-geographical regionalization schemes of the territory of the Russian Federation. The identified ecoregions can serve as a basis for establishing new greenhouse gas monitoring sites in forest ecosystems.

A detailed study of Devonian rock outcrops in western Spitsbergen (Dickson Land) was conducted during the expedition in the Pyramiden mine area to identify and select palaeosols. The studies of pre-Quaternary palaeosols on the Spitsbergen archipelago were initiated due to the completeness of the Devonian geological section and the abundance of palaeobotanical finds. Devonian palaeosols and pedocomplexes were discovered in the valleys of the Muninelva, Torelva and Hugindalen rivers, and palaeosol samples were collected over a wide geological interval (D₁–D₃). The palaeosols are characterized by a complete profile and the preservation of plant imprints and, in some cases, plant tissues. The studied objects represent palaeosols of various genesis. The obtained research results indicate that the continental formation is widely represented in the Devonian deposits of the archipelago. The analytical results allow us to reconstruct terrestrial ecosystems and climate on the Spitsbergen archipelago in the Devonian and, in the future, when accumulating information, to compare them with the palaeosol data accumulated over the last decade for the Central Devonian field (European part of the Russian Federation) and to expand our understanding of the Earth's soil cover and climatic zonality of the past.

Based on geostrophic current fields calculated from altimetry data for the period from January 1, 2013, to December 31, 2023, numerical modeling of the advection of potentially contaminated water from the Kashiwazaki-Kariwa Nuclear Power Plant to the shores of Primorsky Krai and the fishing zone around Southern Kuril Islands was carried out using a Lagrangian approach. Dasymetric maps representing probable pathways of surface ocean contamination were constructed. For the southern Primorye region, transport pathways and three corridors related to the local current structures and mesoscale eddies were identified. The minimum advection time for Lagrangian markers simulating potentially contaminated waters to reach the Primorsky Krai coast is 138–140 days. Two possible transport routes into the Southern Kuril fishing zone were revealed, with the potential for rapid advection of contaminated markers into this zone within 58–60 days. It was demonstrated that the advection of Lagrangian markers occurs in portions and within specific time windows.