Gas composition of bottom sediments of the Laptev-Siberian Sea geostructural zone (LSZ) was determined to include: helium and hydrogen in concentrations of 0.0028-0.2092 and 0.0012-0.8727 cm3/kg, hydrogen sulfide - 0.0006-0.0072, carbon monoxide - 0.0016-0.0577, carbon dioxide - 0.1482-21.1602, methane - 0.0017-8.3047 and its homologues (in total) - 0.00001-0.0355 cm3/kg. It was found that the values of average concentrations of gases in bottom sediments increase with the depth of their occurrence and exceed the anomaly criteria identified for the East Arctic shelf by 2.6-27.7 times, including: CO2, CO and H2S - by 2.6, 3.0 and 3.4 times, Sigma C2-C5 and He - by 9.3 and 10.8 times, CH4 - by 27.7 times; this actually indicates a high degree of gas saturation of bottom sediments of the region. The formation of CO2, CO, H2S, H2, CH4 and Sigma C2-C5 anomalies in sediments of the upper and the base of the middle sampling horizon is determined by relatively high contents of sapropelic and humic organic matter and gas influx from the lower horizon. Distribution of anomalies with maximum concentrations of natural gases and He in sediments of the lower horizon, with minimum contents of Corg, is associated with zones of faults, large dislocations, tectono-magmatic and seismic activity, which are the main routes of diffusion-migration of gas transfer to bottom sediments. Formation of concentrations of gases and their anomalies in sediments of the LSZ follows the rules of additivity, i.e. successive accumulation of migratory natural gases of different genesis with prevalence of gas phase and isotopic indicators of more gas-saturated parental source, epigenetic and syngenetic to sediments. It was found that maximum values of average gas saturation with CH4, Sigma & Scy;2-& Scy;5, He and H2 in LSZ are typical for bottom sediments of the flanks of troughs, CO and CO2 - for the arch parts of uplifts. In sediments of monoclinal folds (structural terraces), minimal values of average gas saturation are observed, with the exception of the South Anyui Fault Zone. In general, gas saturation of LSZ sediments is determined by the complex impact of geological factors, with the major ones being: gas content of rock complexes and gas saturation of underlying sediments, fault and fold tectonics, a high degree of tectono-magmatic and seismic activity, a geostructural position, coal content, oil and gas content, as well as the depth of occurrence, organic saturation and material composition of OM in bottom sediments. The influence of the latter predetermined the formation and distribution of five geochemical fields of CH4, three of CO, Sigma & Scy;2-& Scy;5, He and one of CO2, and one of H2 in LSZ.

This work presents new data on the composition and concentrations of hydrocarbon gases in the upper horizons of bottom sediments of Avacha Bay and the adjacent zone of the Pacific Ocean. The established concentrations of methane and the sums of its homologues are highly variable, from 0.0003 to 120.9385 and from 0.00005 to 0.00753 cm3/kg. Gas anomalies are formed in the sediments of the shallow shelf (Avacha Bay, Russkaya Bay, Vilyuchinskaya Bay and Listvennichnaya Bay) and in the outer shelf and the continental slope at sea depths of 14–800 m and sampling depths of 3–50 cm. The data on the isotopic composition of carbon δ13C–CH4 from –78.1 to –33.4‰ and δ13C–CO2 from –19.8 to –11.1‰ indicate the formation of natural gases of various polygenetic (mixed) origin in the bottom sediments of the region and, with a high probability, their significant influx from the underlying sediments.

The results of the generalization and scientific analysis of gas-geochemical studies of hydrocarbon gases in the bottom sediments of the eastern sector of the Laptev and the East Siberian Seas are presented. In the course of studies, methane and the sum of its homologs were found in the sediments of the region in the concentrations of 0.0010–12.1502 and 0.000002–0.03626 cm3/kg. In general, the distribution of hydrocarbon gases in the bottom sediments is characterized by significant variability and the formation of local, linear and areal hydrocarbon anomalies. This fact is explained by the presence of underlying gas-saturated indigenous sources, tectonic conditions, seismic activity, geostructural position, sediment occurrence depth, and the influence of other geological factors. Based on the generalization and analysis of the authors’ data, a map of the distribution of hydrocarbon gases in the bottom sediments of the central part of the East Arctic shelf was compiled for the first time.

-In bottom sediments of the New Siberian sedimentary basin and adjacent geostructures of the East Siberian Sea, we identified & Scy;& Ncy;4, as well as its limit and unsaturated homologues (up to and including C5H12), CO2, CO, H2, He, H2S, O2, N2, and Ar. Isotope-gas-geochemical parameters delta 13 & Scy; & Scy;& Ocy;2, & Scy;& Ncy;4 and & Scy;2 & Ncy;6, of the molecular mass of hydrocarbon fraction and genetic coefficients indicate the presence of both syngenetic and epigenetic gases of various gas sources in sediments, including recent sediments, peatlands, coal-bearing and gas-bearing formations, solid bitumen, igneous formations, accumulations of gas hydrates and prognostic condensate-gas, condensate, oil-and-gas and gas-and-oil reservoirs. Concentrations of CO2 and CO reach 29.25 and 0.06 cm3/kg, CH4 and the sum of its homologues - 5.93 and 0.031, & Ncy;2 and He - 0.78 and 0.318, H2S - 0.092 cm3/kg; this indicates that gas-geochemical anomalies, exceeding the anomaly criteria by 6-124 times, form in bottom sediments. The formation and distribution of abnormal concentrations of natural gases depend on the complex influence of gas-controlling factors - geological structure, fold and fault tectonics, magmatism, coal-oil-gas content, bituminous content, organic saturation, lithological composition, water-physical and reservoir properties of sediments, hydrogeological, geocryological and other conditions for accumulation of natural gases or their degassing.

В донных отложениях Новосибирского осадочного бассейна и прилегающих геоструктур Восточно-Сибирского моря установлены СН4, а также его предельные и непредельные гомологи (до С5Н12 включительно), СО2, СО, Н2, Не, Н2S, О2, N2 и Ar. Изотопно-газогеохимические показатели δ13С СО2, СН4и С2Н6, молекулярной массы углеводородной фракции и генетических коэффициентов свидетельствуют о наличии в осадках как сингенетических, так и эпигенетических газов различных газоматеринских источни­ков, в том числе современных осадков, торфяников, углегазоносных и газоносных формаций, твердых битумов, магматических образований, скоплений газогидратов и предполагаемых конденсатно-газовых, конденсатных, нефтегазовых и газонефтяных залежей. Концентрации СО2и СО достигают 29.25 и 0.06 см3/кг, СН4 и суммы его гомологов — 5.93 и 0.031, Н2 и Не — 0.78 и 0.318, H2S — 0.092 см3/кг, что указывает на формирование в донных осадках газогеохимических аномалий, превышающих критерии аномальности в 6—124 раза. Формирование и распределение аномальных концентраций природных газов зависит от комплексного влияния газоконтролирующих факторов — геологического строения, складчатой и разрывной тектоники, магматизма, угленефтегазоносности, битуминозности, органической насыщенности, литологического состава, водно-физических и коллекторских свойств отложений, гидрогеологических, геокриологических и других условий накопления и аккумуляции природных газов или их дегазации. In bottom sediments of the New Siberian sedimentary basin and adjacent geostructures of the East Siberian Sea, we identified СН4, as well as its limit and unsaturated homologues (up to and including C5H12), CO2, CO, H2, He, H2S, O2, N2, and Ar. Isotope-gas-geochemical parameters δ13С СО2, СН4and С2Н6, of the molecular mass of hydrocarbon fraction and genetic coefficients indicate the presence of both syngenetic and epigenetic gases of various gas sources in sediments, including recent sediments, peatlands, coal-bearing and gas-bearing formations, solid bitumen, igneous formations, accumulations of gas hydrates and prognostic condensate-gas, condensate, oil-and-gas and gas-and-oil reservoirs. Concentrations of CO2 and CO reach 29.25 and 0.06 cm3/kg, CH4 and the sum of its homologues – 5.93 and 0.031, Н2and He – 0.78 and 0.318, H2S – 0.092 cm3/kg; this indicates that gas-geochemical anomalies, exceeding the anomaly criteria by 6–124 times, form in bottom sediments. The formation and distribution of abnormal concentrations of natural gases depend on the complex influence of gas-controlling factors – geological structure, fold and fault tectonics, magmatism, coal-oil-gas content, bituminous content, organic saturation, lithological composition, water-physical and reservoir properties of sediments, hydrogeological, geocryological and other conditions for accumulation of natural gases or their degassing.

On the basis of lithological and gas geochemical studies and a comprehensive interpretation of the available materials, the main factors of the formation and distribution of grain size distribution, water-physical properties, organic saturation, concentrations and geochemical parameters of hydrocarbon gases in seafloor sediments of geostructures of the western part of the East Siberian Sea are summarized and analyzed. It has been established that the sediments of the northern and central parts of the study area are represented by aleurite-pelites, the southern ‒ by aleurite-pelite-psamites with variations in Corg values ‒ 0.6–2.0%, natural humidity and density ‒ 18–43% and 1.5–2.0 g/cm3, open porosity ‒ 17–33%, the concentrations of methane and its homologues are 0.001–5.934 and 0.00003–0.0312 cm3/kg, the molecular mass of the hydrocarbons fraction, the “wetness”, “dryness” coefficients, and the coefficients of the transformation are 16.05–22.6 g/mol, 0.2–51%, 1–1999, 0.2–50.8 and δ13С‒СН4 (–82.7…–38.4‰). Based on the values of gas geochemical parameters, eleven types of gas sources were identified in bottom sediments. In the process of research, it was found that the formation of hydrocarbon anomalies in sediments is mainly associated with their reservoir properties, Corg content and depths of their sampling, as well as with the complex influence of geological factors, the main of which are the gas saturation of the underlying sediments and the type of gas sources, discontinuous and plicative tectonics, geostructures position, thickness of Quaternary deposits, coal and gas content and age of the folded base. To a lesser extent, anomalies of hydrocarbon gases are associated with the lithological composition and density parameters of sediments.

The paper is devoted to comparative analysis of detailed gas-geochemical studies carried out in the Alekseev Bay (Peter the Great Gulf, Japan Sea) in 1989 and 2022. The distribution of methane and carbon dioxide in water is given in details. CTD measurements were made to determine water temperature and salinity. The main regularities in the distribution of gas geochemical fields in the Alekseev Bay (Peter the Great Gulf) are shown basing on the available geological information, taking into account the materials of the predecessors. The results obtained are in demand both in theoretical studies of the gas geochemical fields distribution on the Earth’s surface in connection with the seismotectonic and geological features of the region, and in the practice of developing methods and technologies for measuring the balance flows of the main greenhouse gases, emission and absorption. The results are also relevant for the implementation of research programs within the “climate agenda.”

Geochemical data are presented on the Pleistocene sediments from the central part of the outer shelf of the East Siberian Sea, the continental slope and Podvodnikov Basin of the Arctic Ocean. The studied sediments of the outer shelf and continental slope belong to the aleuropelitic type, while those of the shelf edge and the Podvodnikov Basin, to the pelitoaleuritic type. The contents of the psammitic fraction and stone material do not exceed 10 and 1%, respectively. These features predetermine the distribution of the maximum sediment density and median diameters in the sediments of the outer shelf, and the minimum values in the Podvodnikov Basin. The distribution of Corg and Сcarb contents in the studied sediments is characterized by a similar variability. The average wetness content in the bottom sediments in the study area systematically increases in the “shelf–pelagial” direction. The study of the chemical and gas composition of the bottom sediments in the same direction made it possible to distinguish four main groups of geochemical associations in the Pleistocene sediments of the study area. The bottom sediments of the outer shelf are characterized by the maximum concentrations of the first group of chemical elements (Si, Sr, Ba) and methane (up to 0.102 cm3/kg), those of the shelf edge, by the maximum concentrations of the second group (Cd, Hg, U, K, Ca) and the minimum content of methane (up to 0.002 cm3/kg). The sediments of the continental slope have the maximum concentrations of the third group (Cu, Zn, Ti, Be, Nb, Ag, Tl, Pb, Lu, Tm, Tb, Ho, Eu, Yb, Er, Dy), while those of the Podvodnikov Basin, the fourth group (Mn, Fe, Al, Cr, P, Mg, Mo, Ni, Sb, Sn, As, Th, Co, Ga, W, Hf, Rb, V, Cs, Sc, Li, Gd, Sm, Pr, Nd, La, and Ce) and intermediate contents of methane (up to 0.051 cm3/kg). The maximum total concentration of methane homologues (up to С5 including, 0.006 cm3/kg), δ13С-СН4 (up to –36.0‰), δ13С-С2Н6 (up to –17.2‰), molecular mass of the hydrocarbon fraction (up to 27.5 g/mol), coefficient of transformation and “wetness” of the hydrocarbon fraction were found in the Pleistocene sediments of the continental slope and the foot of the Podvodnikov Basin, while the lowest concentrations of these parameters were determined in the outer shelf. The established isotope-gas-geochemical indicators point to the predominance of epigenetic hydrocarbon gases from various gas sources in the studied sediments. The positive and negative correlations between geochemical and isotopic-gas-geochemical indicators have been established. Obtained data were used to estimate the oil and gas prospects of the study area.

We present research results for the geologic structure of the De Long, Aion, and Pegtymel sedimentary basins of the East Siberian Sea. The materials of geological surveys and drilling in their land area and island surroundings, the data obtained from geophysical surveys conducted by Dal'morneftegeofizika, MAGE, and Sevmorgeologiya, and the seismic and deep-drilling data on the U.S. sector of the Chukchi Sea are summarized and analyzed. Pre-Paleozoic strata and the sedimentary cover have been identified throughout the sections of the sedimentary basins, which suggests the existence of a geologic "cover-basement" boundary rather than an arbitrary called "acoustic basement" horizon. The data on the geologic structure and gas saturation of the upper parts of the sedimentary sections were obtained during the study and gas-geochemical testing of core samples and bottom sediments from coastal shallow wells and corers. Gas contained in the rocks and bottom sediments in the study area includes hydrocarbon gases (HCGs) (CH4, C-2-C-5, and their unsaturated homologues), CO2, H-2, He, N-2, Ar, and, seldom, CO and H2S. The data on gas saturation of bottom sediments and the geochemical parameters of their syngenetic and epigenetic gases are presented. Areas of abnormal saturation of sediments with CO2, CH4, other HCGs, H-2, and He (>5, 0.05, 0.001, 0.005, and 0.005 cm(3)/kg, respectively) have been identified, and maps of the gas saturation patterns in bottom sediments have been compiled. It is established that both gas saturation and distribution are determined mainly by the geologic evolution, tectonics, magmatism, geocryologic conditions, lithologic composition, catagenesis, coal content, bituminosity of sedimentary rocks, and oil and gas potential of the study area.

This paper reports new data on the composition of hydrocarbon gases in bottom sediments of the Laptev–East Siberian marginal shelf transition zone, the continental slope of the Lomonosov Ridge, and Podvodnikov Basin of the Arctic Ocean. Anomalous concentrations of methane and hydrocarbon gases (up to C5 inclusive) have been established. Gas-geochemical indicators of eight genetic groups of hydrocarbon gases have been determined. The oil-and-gas content of the study area has been predicted based on the data obtained.

New data on the gas and chemical composition of bottom sediments of the marginal-shelf part of the East Siberian Sea, continental slope, and Podvodnikov Basin of the Arctic Ocean are presented. The genetic parameters of seven groups of epigenetic hydrocarbon gases are determined. The distribution areas of the potential oil–gas, gas–oil, and oil deposits have been revealed. Three groups of chemical elements have been specified in bottom sediments. Their maximum concentrations are related to particular geostructures of the area studied.

The results of gas-geochemical studies of the Chaun Depression and the Ayon sedimentary basin of the East Siberian Sea are presented. The natural gas composition in rocks, gas manifestations, and bottom sediments is determined. The indicators of the molecular mass of hydrocarbon fractions and weight concentrations of individual hydrocarbons, in which ratios are of correlation-genetic significance for hydrocarbon gases of the geological formations, are identified. The geochemical classification of hydrocarbon gases from bottom sediments and a schematic map of gas geochemical zoning of the study area are presented. The oil and gas potential of the Chaun Depression and the Ayon sedimentary basin is evaluated.

We report methane concentrations in the bottom water layer and the upper layer of bottom sediments and the results of acoustic explorations of methane seeps on the shelf bordering the continental slope of the Sea of Japan region, in which electromagnetic Schumann’s resonance oscillations were earlier recorded at continental-slope water depths of 500, 1000, and 2000 m. The occurrence of Schumann’s resonances at such great depths is explained by an increase (a factor of more than 25) in the electrical resistivity of a ~2000 m thick sediment layer with the pore space largely filled with free methane. A new method is proposed for determining the depth of the sources of anomalous concentrations of methane in bottom sediments or in the bottom water layer on a deep shelf. The method is based on recording Schumann’s resonances during measurements of the natural electric field at a series of increasing depths in areas bordering the continental slope.

Anomalous concentrations of dissolved gases, exceeding their background values by an order of magnitude or more, are recorded in the surface and ground waters of the Birofeld Graben of the Middle Amur sedimentary basin. The main geological factors that influence the formation of the gas composition and gas saturation of waters are determined. The gas-geochemical indicators for the dissolved hydrocarbon gases, which make it possible to estimate their genesis and prospects for the oil-and-gas contents of the Birofeld graben, are specified.

The work reports on the results of geochemical studies of the bottom sediments on the shelf of the East Siberian Sea. The sediments’ gas content, gas composition, and gas geochemical and isotopic characteristics are determined. Abnormal zones of distribution of methane, hydrocarbon gases, and carbon dioxide are revealed within the studied areas, along with the general geological factors affecting gas formation. Areas of distribution of hydrocarbon gases of varying origins are distinguished. The potential for oil-and-gas content is estimated.