Methane is a powerful greenhouse gas, and the abrupt degassing events that recently have formed large craters on the Russian Arctic Yamal and Gydan Peninsulas have caused major concern. Here we present field data on cover sediments and evolution of a gas-emission crater discovered in the Erkuta–Yakha River valley in the southern Yamal Peninsula in June 2017. The crater is located south of other similar craters discovered over the past decade in northern West Siberia. Data were collected during a field trip to the Erkuta crater in December 2017 which included field observations and sampling of permafrost soil and ground ice from the rim of the crater. All soil and ice samples were measured for contents of methane and its homologs (ethane and propane) and carbon dioxide. The contents of carbon dioxide in some samples are notably higher than methane. The strongly negative δ13С of methane from ground ice samples (−72‰) is typical of biogenic hydrocarbons. The ratio of methane to the total amount of its homologs indicate a component of gases that have migrated from a deeper, thermogenic source. Based on obtained results, a potential formation model for Erkuta gas-emission crater is proposed, which considers the combined effect of deep-seated (deep gas migration) and shallow (oxbow lake evolution and closed talik freezing) causes. This model includes several stages from geological prerequisites to the lake formation.

Gas accumulation and pressurized unfrozen rocks under lakes (sublake taliks) subject to freezing in shallow permafrost may lead to explosive gas emissions and the formation of craters. Gas inputs into taliks may have several sources: microbially-mediated recycling of organic matter, dissociation of intrapermafrost gas hydrates, and migration of subpermafrost and deep gases through permeable zones in a deformed crust. The cryogenic concentration of gas increases the pore pressure in the freezing gas-saturated talik. The gradual pressure buildup within the confined talik causes creep (ductile) deformation of the overlying permafrost and produces a mound on the surface. As the pore pressure in the freezing talik surpasses the permafrost strength, the gas-water-soil mixture of the talik erupts explosively and a crater forms where the mound was. The critical pressure in the confined gas-saturated talik (2–2.5 MPa for methane) corresponds to the onset of gas hydrate formation. The conditions of gas accumulation and excess pressure in freezing closed taliks in shallow permafrost, which may be responsible for explosive gas emissions and the formation of craters, are described by several models.

The study of organic matter content and composition in source rocks using the methods of organic geochemistry is an important part of unconventional reservoir characterization. The aim of this work was the structural group analysis of organic matter directly in the source rock in combination with a quantitative assessment and surface distribution analysis of the rock sample by FTIR spectroscopy and FTIR microscopy. We have developed new experimental procedures for semi-quantitative assessment of the organic matter content, composition and distribution in the source rocks and applied these procedures for the study of the samples from the Bazhenov shale formation (West Siberia, Russia). The results have been verified using the data from the study of organic matter obtained by Rock-Eval pyrolysis and differential thermal analysis. The obtained results demonstrate the prospects of FTIR spectroscopy and FTIR microscopy application for non-destructive and express analysis of the chemical structure and distribution of organic matter in rocks.

In this study, we identified the luminescent layers containing a significant amount of alginite in the Upper Jurassic–Lower Cretaceous Bazhenov Formation named “the alginite-rich layers”. Lithological and geochemical methods were used to determine distinctive features of these layers and to evaluate their impact on the total petroleum generation potential of the Bazhenov Formation. We have shown that the composition of the alginite-rich layers differs significantly from the organic-rich siliceous Bazhenov rocks. Rock-Eval pyrolysis, bulk kinetics of thermal decomposition, elemental analysis, and the composition of pyrolysis products indicate type I kerogen to be the predominant component of the organic matter (OM). Isotope composition of carbon, nitrogen, and sulfur was used to provide insights into their origin and formation pathways. The luminescent alginite-rich layers proved to be good regional stratigraphic markers of the Bazhenov Formation due to widespread distribution over the central part of Western Siberia. They can also be applied for maturity evaluation of the deposits from immature to middle of the oil window, since the luminescence of the layers changes the color and intensity during maturation.

The role of thermal petrophysics in modelling basin and petroleum systems has been growing in recent years for at least three major reasons. First, the results of deep continental scientific drilling have led to dramatic changes in the understanding of the thermal regime at substantial depths in the interior of the Earth (Emmerman & Lauterjung, 1997; Popov, Popov, Chekhonin, Spasennykh, & Goncharov, 2019). Second, temperature is a key parameter for determining the transformation of kerogen into oil and gas, and its evaluation is impossible without reliable data on thermal properties. The most sophisticated and appropriate modelling techniques for analysing thermal histories and organic maturation levels may fail when applied to real basins if the thermal conductivity

Gas-emission craters discovered in northern West Siberia may arise under a specific combination of shallow and deep-seated permafrost conditions. A formation model for such craters is suggested based on cryological and geological data from the Yamal Peninsula, where shallow permafrost encloses thick ground ice and lenses of intra- and subpermafrost saline cold water (cryopegs). Additionally, the permafrost in the area is highly saturated with gas and stores large accumulations of hydrocarbons that release gas-water fluids rising to the surface through faulted and fractured crusts. Gas emission craters in the Arctic can form in the presence of gas-filled cavities in ground ice caused by climate warming, rich sources of gas that can migrate and accumulate under pressure in the cavities, intrapermafrost gas-water fluids that circulate more rapidly in degrading permafrost, or weak permafrost caps over gas pools.

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Physical chemical characteristics of the Solnechnoye tin deposit hydrothermal system have been stud ied. Ores of cassiterite-tourmaline type was formed in a vertically dipping fracture zone, extended up to 8 km in a metamorphosed mass of sandstone-shale rocks. This rock mass transfers in its root part to a granitoid massif (quartz diorites-monzonites).The evolution in composition of the mineral-forming solution was studied by gas-chromatographic analysis of gaseous phase of fluid inclusions. The analysis of aqueous extracts from fluid inclusions (AAS, potentiometry, ICP and ionic chromatography) was also performed. It was found that as the process proceeded from the preore quartz-tourmaline stage to productive quartz-cassiterite, the values of axco-' a(s11), C02/CH4, HCO3/Cl and pH increased. The value of foe corresponded to the F-Q-M buffer on thie preore stage and increased up to that of the Ni-NiO buffer during the formation of the main part of cassiterite ores.Study of organic compounds showed that a greater degree of oxidation in comparison to the preore stage is typical for the quartz-cassiterite and the main sulfide stages. It means that organic compounds participated in redox reactions which took place in the solutions during the precipitation of these mineral assemblages.The 8180 values of fluids calculated from the 8180 values obtained for the minerals show a distinct trend of decrease toward later stages. The 8D values for the waters from the inclusions are close to those found for contemporary meteoric waters (-120%o). A transport model of non-isothermal isotope exchange between water and arbitrary number of minerals along the fluid flow paths was used for the interpretation of these isotope data as well as of the data on the isotope composition of the wall-rocks. Descending flow of meteoric waters was found to interact with sandstone-shale rocks and with granitoids before entering into the discharge zone. Thus while studying reasons of ore formation in a given hydrothermal system it is necessary to answer subsequently several questions: a) what are the main changes in the physical chemical prop erties of fluid in the process of the ore formation; b) which of the factors plays the decisive role in the deposition of ore material; c) with which re actions these changes are coupled; and d) which properties of the hydrothermal system are respon sible for the changes of physical chemical condi tions in the solutions. Large economic tin deposit Solnechnoye was chosen for the main object of our study. This de posit is a typical representative of tourmaline type of cassiterite-silicate formation according to the classification (Lugov et al., 1976). Some ques tions of geological structure, chemical and miner alogical compositions of this deposit have been discussed by several authors (Gonevchuk et al., 1984). Many papers (Bannikova et al., 1984(Bannikova et al., , 1989Kokorina, 1982;Sushchevskaya et al., 1978Sushchevskaya et al., , 1984 are dedicated to the problems of physical chemi cal conditions of its for...