All Russian Research Institute of Geology and Mineral Resources of the World Ocean

A layer (260–270 cm) of soft carbonate nodules containing numerous valves of ancient diatoms was discovered in bottom sediments of the Bolshaya Zelenovskaya oil-methane seep (Central Baikal). Various methods confirmed the presence of a siderite phase in the carbonate; their enrichment in the heavy isotope δ13C (+14‰ VPDB) and the light isotope δ18O (−8.43‰ VPDB) also has been detected. Carbonate precipitation could have been facilitated by the high organic matter content of ancient diatoms, dissolved inorganic carbon, or CO2, supplied by the flow of mineralized fluids and formed during methanogenesis. High-throughput sequencing of the variable region of the 16S rRNA gene revealed the dominance of archaea of the family Methanoregulaceae (11–35%) and of the class Bathyarchaeia (16–54%) with a significant contribution of representatives of Nitrososphaeria (18%) and Woesearchaeales (10%) in the surface sample, as well as of Hadarchaeota (12%) in the deep carbonate-containing sediment. Bacterial dominants were represented by the phyla Chloroflexota (14–30%) and Acidobacteriota (5.8–11%), as well as representatives of Pseudomonadota (32%) in the surface sample and of Artibacterota (28.5%) in the carbonate-containing sediment. Based on the isotopic composition of δ18O and δ13C, chemical composition of pore waters, and microbial diversity, the manuscript discusses the possible scenario of carbonate precipitation process.

The research into a difficult-to-reach region of Antarctica in a mountain frame of the Denman Glacier has revealed the presence of Paleoarchean and Neoarchean granite-gneiss blocks comparable to other protocratons of East Antarctica and the Earth as a whole, which is particularly relevant in the context of problems of Archean geodynamics and determining the evolutionary stages of the early continental crust. The results of U–Pb geochronological dating and Sm–Nd isotope systematics of a wide range of rocks of two Archean domains and tectonically framing fragments of the mobile belts are presented. The Paleoarchean age (3276.6 ± 29 Ma) of tonalitic gneiss protoliths in the Davis Terrane has been confirmed. For the first time, sillimanite-garnet paragneisses were identified within the terrane on Cape Charcot, with the maximum sedimentation age of their protolith dated to 3166 ± 21 Ma. Rifting of the crust in the range of 2960–2800 Ma is confirmed by metamorphic rims of zircons in gneisses and crystalline schists aged 2956 ± 21, 2870 ± 21 Ma, respectively. The consolidation of the Davis Protocraton occurred at the Mesoarchean-Neoarchean boundary, and the final stage of formation reflected in Pan-African thermal processes 545–487 Ma ago. The early stage of the Obruchev Neoarchean Terrane formation, first recorded on the Cape Jones, is associated with the crystallization of orthogneiss protoliths 2711 ± 8.9 Ma ago. Tectono-thermal events of the accretionary-collisional regime are constrained to the interval of 1190–1140 Ma, corresponding to the development of the Wilkes Mobile Belt, which correlates with the Albany-Fraser Orogeny in Australia. The ancient Davis and Obruchev protocratons developed independently of each other at the Archean-Mesoproterozoic stage of geodynamic evolution. The amalgamation of the Davis and Obruchev domains into a collage was associated with the final stage of the Rayner orogeny and the integration of Antarctica into the Rodinia supercontinent 1150–900 Ma ago.

The paper presents a review of the studies carried out in the area of the subglacial Lake Vostok (East Antarctica) to date. They include geophysical, glaciological, geodesic, and geological investigations. The most important geophysical investigations were carried out by the Polar Marine Geosurvey Expedition. They included reflection and refraction seismic, and also radio-echo sounding. The major contribution to the study of this region was made by American researchers, who in the 2000/01 field season performed a complex airborne geophysical survey on a regular network. Their work included magnetometric, gravimetric, and radio-echo sounding measurements. All the research conducted found that the water surface area is 15 790 km², and its altitudinal height changes from –600 to –150 m. The average depth of Lake Vostok is 400 m, and the maximum marks reach 1 200 m. The water body volume is estimated at 6 100 km³. There are 11 islands in the lake, and their total area is 365 km². In addition, 56 isolated subglacial water bodies were found around the lake. A special section is devoted to a review of mathematical models of heat and mass transfer processes in the glacier and water movement in Lake Vostok.

The paper is based on additional studies of mineral inclusions in the accretion ice sampled by deep drilling at Vostok Station in central Antarctica. The studies include X-ray microtomography of two mineral inclusions with identification of their mineral composition; analysis of clay minerals in the soft aggregate of the largest inclusion; and geochronological study of zircon grains. X-ray microtomography shows intact morphology of the inclusions in the ice core and their internal texture. The soft aggregate of the largest inclusion is characterized by the dominance of illite, intermediate concentrations of chlorite and small amounts of kaolinite. A notable feature is the absence of mixed-layer minerals typical of Antarctic coastal areas. The most valuable information is derived from new geochronological data and their integration with previous dating data. The detrital zircon U-Pb ages show strong probability peaks between 900 and 1100 Ma, while the detrital monazite ages are clustered between 1250 and 1450 Ma. Both of these age intervals correspond to the Rayner Orogeny.

The conditions for the formation of gas hydrates associated to subsea permafrost in the Kara Sea are predicted based on numerical modeling. The forecast of the distribution of the relic submarine permafrost and related methane hydrate stability zone is given on the basis of solving the equation of thermal conductivity. According to modeling data, an extensive thermobaric relict submarine permafrost zone is predicted within the Kara Sea shelf. The greatest thickness (up to 600 m) of the permafrost is confined to the Taimyr shelf. Based on the results of the analysis of our model, drilling seismic data, the southwestern shelf of the Kara Sea is characterized by insular or sporadic permafrost. In the northeastern part, the nature of permafrost is also discontinuous, despite the greater thickness of the frozen strata. For the first time, accumulations of cryogenic gas hydrates on the Taimyr shelf have been characterized. The new drilling data obtained, seismic data reinterpretaion and numerical modeling have shown that the gas hydrate reservoir is confined to unconformably occurring Silurian‒Devonian and underlying Triassic-Jurassic strata. The thickness of the gas hydrate reservoir varies from 800 to 1100 m. Based on the interpretation of CDP data and their comparison with model calculations, frozen deposits and sub-permafrost traps of stratigraphic, anticline and anticline-stratigraphic types were identified for the first time. These pioneering studies allowed to characterize the thickness and morphology of the gas hydrate reservoir, giving a preliminary seismostratigraphic reference, and to identify the potentially gas-hydrate bearing structures. Due to favorable thermobaric and permafrost-geothermal conditions, most of the identified traps may turn out to be sub-permafrost accumulations of gas hydrates. In total, at least five potential accumulations of gas hydrates were discovered, confined to structural depressions ‒ Uedineniya Trough and its side included Egiazarov Step and North Mikhailovskaya Depression.

The article addresses issues related to the study of lithodynamic processes on the shelf as dangerous phenomena. On the example of the coastal zones of South Sakhalin where hazardous exogenous processes on the shelf are state-monitored, it is shown that an annual redistribution of bottom sediment accumulation and erosion zones occurs within the identified key areas. Other examples from the practice of similar works in the Gulf of Finland of the Baltic Sea indicate that lithodynamic processes in the coastal zone lead to a significant disturbance of the coast, which poses a specific danger to the population. It is concluded that lithodynamic processes should be studied via standard lithological and geophysical methods used in marine geological work.

An overview of Russian studies of deep-sea polymetallic sulfides (PМS) in the axial zone of the Mid-Atlantic Ridge (MAR) at the Russian Exploration Area (REA‒PMS) is presented. A brief geological description of the axial zone of the MAR and PMS sites discovered and studied for almost forty years before and after the signing of an exploration contract with the International Seabed Authority in 2012 is given. Information on methods for conducting searches and exploration of PMS, technical equipment, as well as on metallurgical processing of raw materials is presented.

Abstract The Alpha-Mendeleev Rise is located in the Amerasia Basin. The work is based on a synthesis of interpretation of regional 2D MCS seismic profiles and data from rock sampling using special underwater vehicles on the slopes of seamounts. The Rise is represented by alternation of highs (horsts) and half-grabens. At the base of the horst cover, bright reflectors are distinguished, which are interpreted as volcanics. Half-graben sections are wedge-shaped and are similar in geometry to seaward-dipping reflectors (SDRs) of continental passive volcanic margins. Rock sampling has shown that the horsts are composed of sedimentary rocks of Paleozoic age, penetrated by intrusions. Aptian-Albian sections with volcanics (basalts, trachybasalts, trachyandesites) were identified on the horsts. U/Pb dating of igneous rocks showed that typical age of rocks is 110-114 Ma. Magmatic Cretaceous rocks contain zircons with ages ranging from pre-Barremian Mesozoic to Precambrian. The presence of these ancient zircons indicates that the Alpha-Mendeleev Rise is composed of continental crust. A model of the crustal structure of the Alpha-Mendeleev Rise is proposed. The upper and lower crust is approximately 20-30% saturated with intrusions of basic composition. At the base of the crust, a high-velocity layer up to 5 km thick is distinguished.