Isotopic studies are currently among the most prioritized methods for addressing critical challenges in petroleum geology, particularly in determining the nature and sources of organic matter. This paper briefly presents the results of utilizing isotopic markers in addressing issues related to: stratigraphic correlation, geochemical characterization of organic matter, and fluid dynamic reconstruction. The isotopic effects (δ18О, δ13С) observed in the study of Meso-Cenozoic sections in Crimea and the Western Pre-Caucasus have enabled the identification of global events, facilitating detailed stratigraphic correlation. Analysis of the isotopic-geochemical characteristics (δ13С) of fluids from sedimentary formations of varying ages allowed for the determination of formation conditions, the genesis of organic matter, and its geochemical classification for a group of fields at Kamennaya Vershina (Western Siberia). By integrating geochemical vertical zonality, evidence of hydrocarbon mixing from different origins, and the detection of localized thermal anomalies based on isotopic parameters, a comprehensive fluid dynamic model was developed, incorporating previously acquired geological and geophysical data.

An integrated approach to the study of the Maastrichtian deposits of the Darya River (North Caucasus) section served as a basis for reconstructing the sedimentation conditions. As a result of our research, we have made conclusions about the biotic and abiotic events of that time. The stratigraphic position of the section has been clarified and its zonal subdivision by foraminifers has been defined. The paleogeographic and paleoclimatic environments have been reconstructed. It has been revealed that there was a warm-water basin (from shallow-sea to moderately deep-water one) with a normal salinity and an irregular sedimentation rate in the region in the Maastrichtian.

In 2023, comprehensive studies of shallow-water methane gas emissions were conducted during expeditionary work in the coastal area of Laspi Bay (southwestern coast of Crimea). The research included determining the component and isotopic composition of bubble gas, measuring methane concentration in the gas emission area, estimating bubble flux rates, and measuring hydrophysical parameters above the seep site. The obtained results of the carbon isotopic composition of methane and ethane in the studied samples corresponded to (δ13Cmean = –36.0 ± 0.8‰, δ13Cmean = –37.5 ± 0.2‰, respectively) and indicate the presence of thermocatalytic methane migration along fault systems. It was found that the methane seeps of the Crimean coast are relatively low-flow, with a specific flux ranging from 5 to 10 m3 year-1 from an individual seep. The presented temporal dynamics of dissolved СН4 concentration above the seep and changes in the isotopic ratio of δ13C-СН4 in bubble gas indicate the constancy of the process over time and the absence of connection with external hydrological changes in the water area. The obtained ratios of the carbon isotopic composition of methane and ethane demonstrate that the gas mixture was most likely generated from source organic matter of marine origin, and one of the main sources of hydrocarbon fluids is the Upper Eocene and Oligocene deposits in the Western Black Sea basin.

This research quantifies the gas release rate from a natural shallow methane seep site in the Laspi Bay (Black Sea), whose origin is thermocatalytic. An adaptive single bubble identification technique was applied to analyze gas volume and release rates from passive acoustic data. Gas from the seafloor was emitted by single bubbles that occurred in clusters. The frequency of an individual bubble (830 Hz) was proportional to the bubble's radius (0.4 cm), which coincides with the optical method. The active seepage phases lasted longer than the pauses between bubble clusters. Distribution of bubble clusters and pauses duration for all seasons deviated significantly from a normal distribution. The daily and interseasonal periodicities of gas emissions were quite similar. The bubble gas flow rate ranged from 26 to 37 liters per day. Short-term water pressure fluctuations (up to a Δp of 46 mbar) caused by sea swell can impact gas flow variability. Continuous recording of hydrological parameters showed that average dissolved oxygen concentrations and salinity at the background station were slightly higher than those above the seep site. However, the data did not demonstrate significant environmental effects, such as hypoxia or submarine freshwater inflow, which was observed in other seepages areas.

A method of sample decompounding and silver sulfide precipitation for determination of the sulfur isotope composition using mass-spectrometry has been tested and improved. The analytics and methodology of preparing test samples for analysis are described and task variations are indicated. The validity of the developed method of sample preparation was verified by a comparative analysis of various methods in three laboratories using internationally certified rock standards.

There is no consensus on the role of different source rocks (SRs) in the formation of the Krasnoleninskoe field. The main Upper Jurassic-Early Cretaceous SR of Western Siberia is represented on the Krasnoleninsky arch by the Tutleim formation (fm) (J3tt–K1v). It is overlain by argillaceous rocks of the Frolov fm (K1v–K1a), underlain by the Abalak (J2cl–J3km), Tyumen (J2a-b), Sherkalin (J1) formations and folded pre-Jurassic basement. All these formations potentially contain SR layers. The purpose of the article is to determine the sources of oil in the Krasnoleninskoe field by comparing oils with SRs and to determine of the history of oil composition formation. Based on a review of known geochemical parameters and the results of statistical analysis new molecular parameters for determining the type of organic matter (OM) and its maturity are proposed. A secondary processes of the oils of the Vikulov fm of the Kamennaya crest has been established, which is associated with the migration of hydrocarbons from the Vikulov fm to the overlying deposits. It is shown that the oils of the Vikulov fm of Kamennaya crest were formed from the SR, which was at the MC2 substage during the generation of hydrocarbons, and the oils of the Jurassic and pre-Jurassic deposits were formed on the end of MC2-beginning of MC3 substages. It was determined that the oils of Kamennaya crest have aquatic initial OM, aquatic OM was found in the Tutleim and Tyumen SRs. According to the criteria of OM type and its maturity, the source of Kamennaya crest oils cannot be determined; therefore, genetic features of the difference between the aquatic OM of the Tyumen and Tutleim formations were found. These features made it possible to estimate the source of oils for different parts of the Krasnoleninskoe field: for Kamennaya crest the Tutleim fm, for the Talinskaya area the Tyumen fm, for the Em-Egovskaya area, the Tyumen and Tutleim formations. Estimation of the contribution of the Sherkalin and Abalak SRs to the formation of hydrocarbon accumulations is beyond the scope of current work.

The active development of the Crimean region requires the provision of an independent energy system.Currently, there are 36 hydrocarbon fields in Crimea: 12 with natural gas, 9 with oil, 4 with oil and gas, 2 with oil and gascondensate and 9 gascondensate fields (according to www.mygeomap.ru portal by February 10, 2023). Despite the fact that the vast majority of fields are small and some of them werealready under the development it is necessary to consider their potential and production possibility at least for selling products on the domestic market within Crimea peninsula.In the second half of the last century, extensive exploration work was almost completely stopped because small deposits in the drilled structures have been found. Most of the traps of the Mezocenozoic section are complicated bythe faults.The possibility of discovering unexplored yet hydrocarbon resources especially in the lower stratigraphic complexes can be solved due to modern technologies distribution in the area. The contribution of deeper Permian-Triassic and Jurassic complexesto of modern hydrocarbon accumulations formation is poore evaluated and need to be analyzed in more details. Proper setting of geological exploration tasks and conducting modern regional and local seismic surveys will significantly increase the possibility of discovering new hydrocarbon deposits.

— Gas seep and fluid flows from the seabed are an environment-forming factor of the aquatic environment, mainly due to their influence on the dissolved gases in the water, including dissolved oxygen. During the summer seasons from 2019 to 2021 in the area of shallow water gas emission site off the southern coast of the Heracles Peninsula, series of vertical probing profiles were carried out to determine hydrological parameters of the water: dissolved oxygen concentration (O 2 ), temperature ( T ), salinity ( S ), and flow velocity ( U ). The study area is an underwater ledge with faults in the form of three canyons composed of dense limestones, two of which contained bubble gas emissions. Significant variability in O 2 was identified in canyons where gas emissions are observed: from 1 to 80% saturation in the bottom layer, in contrast to normoxia at the background sites. Hypoxia was observed in the bottom layer above the emission sites in the absence of turbulence at temperature stratification. The values S decreased with depth, and the maximum difference reached 0.4‰. The bubble gas was dominated by methane (68.5–75.5%), and the carbon isotope composition of the bubble methane gas varied from –67.9 to –59.8‰ VPDB in 2019 and 2020, respectively. This generally indicates that the CH 4 is of predominantly microbial genesis, was formed under different conditions, and matured in various periods of research during the monitoring period. Bacterial mats (mostly sulfur-oxidizing bacteria) were found in the areas of gas emissions.

Abyssal peridotite outcrops compose vast areas of the ocean floor in the Atlantic, Indian, and Arctic Oceans, where they are an indispensable part of the oceanic crust section formed in the slow-spreading oceanic ridges (Mid-Atlantic Ridge, Southwest Indian Ridge, and Gakkel Ridge). The final stage in the evolution of abyssal peridotites in the oceanic crust is their carbonation, which they experience on the ocean floor surface or near it. The main goal of this study was to reconstruct the geochemical trends accompanying the carbonation of abyssal peridotites using MAR ultramafic rocks as an example and to identify the main factors that determine their geochemical and mineralogical differences. The composition variations of rock-forming minerals and their characteristic assemblages indicate that the initial stages of carbonation of abyssal peridotites occurred in crustal conditions simultaneously with the serpentinization of these rocks. The final stage in the crustal evolution of the abyssal peridotites is their exhumation on the ocean floor where they were brought up along the detachment faults. On the ocean floor, the abyssal peridotites in close association with gabbro form oceanic core complexes, and the degree of their carbonation sharply increases with time of their exposure on the ocean floor. The presented data made it possible to qualitatively reconstruct the sequence of events that determined the mineralogical and geochemical features of carbonatized abyssal peridotites of the MAR.

Both sedimentological factors and secondary processes of lithogenesis influenced the formation of porosity and permeability properties of the reservoir rocks of the Vikulov suite of the Krasnoleninskoe field. The former includes the conditions of sedimentation of the deposits of the Vikulov suite, which at the initial stages of its formation were controlled by the development of a system of incised river valleys, the stages of filling of which, like their composition, have their own characteristics. Also, various genetic types of deposits were formed here. The formation of the upper part of the Vikulov suite took place in a shallow-marine setting, in conditions of storm and wave shallow water, which affected the thin-layered structure of the VK1-3 reservoir. On the other hand, in the sections of a number of wells, dense interlayers are noted, the formation of which is associated with both sedimentation and superimposed processes in lithogenesis, including the formation of hydrocarbon deposits. Therefore, the prediction of the distribution of productive reservoir rocks is the main task when creating a petrophysical model of the field, and to solve this problem, the methods of lithofacies and staged core analysis are used in the work.

The results of a comprehensive study of the boundaries of the Turonian–Coniacian in the Upper Cretaceous deposits of the Abinskii region of the Northwestern Caucasus, composed of rhythmically constructed carbonate strata of the hemipelagic type, are presented. Biostratigraphic analysis of foraminifera complexes made it possible to identify zones in the section that are comparable to those proposed for the Point of the Global Stratotype of the boundary of the Coniacian in Germany. On the basis of chemostratigraphic (isotope) studies, the levels of abiotic events traced in the section and other territories have been established. The Shapsug section, after further study, can be proposed as a possible Hypostratotype (Limitotype) of the Turonian–Coniacian boundary for the territory of the Russian Federation.

Authors used the paleogeographic approach to identify the different facies generation potential, mark out the areas with the highest organic matter and its types, analyse the reservoir quality for oil and gas potential assessment of the Pre-Caucasus basin Khadum formation. The greatest prospects in the Western and Central parts of the basin characterized by terrestrial and partly mixed organic matter types and are associated with the facies of the Sarpinsk-Armavir channel where discharge currents from the Volga-Don basin occurred. The same organic matter types can be related to clastic fans drawn from the north. In the Eastern part the main prospects are associated with unconventional black shale reservoirs with the predominantly aquatic organic matter, isolated on the top and base by the thick series of seal rock.

This article presents modern data on the chemical and gas compositions, as well as the contents of the stable isotopes of oxygen, hydrogen, carbon, and sulfur, in the natural mineral waters of the Essentuki field. A detailed study of the geological and hydrogeological features of the water circulation territory, their macro-component compositions, the contents of organic matter in the water, and the temperature conditions and values of δDSMOW, δ18ОSMOW, δ13СDIC, δ18ОDIC, δ34SVCDT, δ13CCO2, δ13CCH4, and δ15N revealed the genesis of the aqueous, gas, and salt components of the natural mineral waters of the Essentuki field. It was established that all natural mineral waters of the Essentuki field are infiltration meteoric waters. The heterogeneous component composition of the natural mineral waters circulating in various aquifers represents the features of the lithological composition of the water-bearing rocks, the degree of openness or closeness of faults, and the intensity of reactions in the water–rock–gas–organic matter system.

From 2019 to 2021, integrated studies of new shallow-water methane bubble gas seeps were carried out in the coastal zone near Cape Fiolent (Southwest Coast of Crimea). The studies included determination of the hydrocarbon and isotope composition of bubble gas, measurement of the methane and nutrient concentration in the water in the areas of gas seeps, estimation of the value of bubble flows, and measurement of the hydrophysical parameters over the seep sites compared to background areas. A seasonal type of Cape Fiolent methane seeps was noted, and the durations of its active gas emission phases differed in different years. The increased pore water silica concentration at the seep sites and their localization in the vicinity of freshwater slope springs may indicate its association with submarine freshwater discharge in the area. However, no significant desalination of either pore water or the bottom water layer above the seeps was recorded. Dissolved methane concentrations in pore water at seep sites were two orders of magnitude higher compared to the background areas, reaching 448 μmol/L. High values were also obtained for surface water directly above the bubble gas emission points (maximum 353 nmol/L). Multihour monitoring of the hydrophysical parameters above the active seeps showed a decrease in dissolved oxygen compared to the background sites. The maximum difference in O2 concentrations was 3 mg/L. The carbon isotope composition of bubble gas methane δ13C-CH4 (–62.84 to –38.27‰) and carbon dioxide δ13C-CO2 (–16.83 to –10.17‰) corresponded to a mixture of isotopically heavy gas and near-surface isotopically light gas of microbial origin. The question remains open: what are the reasons for the change in the summer active and cold season passive gas emission phases?

The nature of Cretaceous-Eocene boundary is one of the outstanding questions of Crimea Geology. The new data are presented to show that the Cretaceous-Eocene boundary can be established in the Central Crimea very accurately by using the method of quantitative genetic analyses including the Isotope Geochemistry. Integrated lithostratigraphic investigations and Isotope composition of Carbon/Oxygen were conducted on the Cretaceous -Eocene section of the western slope of Ak-Kaya mount (Belogorsk, Crimea). Four layers of different types of rocks were investigated, where the layer 1 and 2 belong to the Maastrichtian, 3 and 4 to the Eocene.The top of the Maastrichtian layer is characterized by a differently oriented fracture system, including large paleoseismic dislocations or a seismogenic trench. The fracture networks are connected and filled with material similar to the Eocene basal horizon including fragments of various sizes of Maastrichtian rocks.Five microfacial types of the collected rock samples were distinguished as a result of microscopic examination. Also X-ray phase analysis, δ13С and δ18О isotopic analysis and X-ray fluorescence analysis were made to specify and compare the mineral composition of Maastrichtian and Eocene rocks. These analyzes allowed to specify paleogeographic conditions. In addition, measurements of fractures in the Cretaceous–Eocene boundary deposits were made to determine the stages of deformation of the whole structure.As a result of the research, it was obtained:1) throughout the entire studied geological interval, sedimentation occurred in a shallow sea of normal salinity. However, conditions were probably more humid in the Eocene, based on lower salinity values.2) Three major stages of deformation were identified: pre-Eocene, Eocene, and post-Eocene.3) The average temperature of the formation of Maastrichtian rocks is 19-22°C, and Eocene rocks is 24-27°C. The increase in temperature up to 38°C during the formation of the Eocene basal horizon may be associated with the global climatic event EECO (Early Eocene Climate Optimum). The synchronicity of the formation of steep submeridional fractures and the basal horizon of the Eocene has been proved. It is shown that the Eocene deformation stage corresponds to the formation of paleoseismic dislocations during the main phase of tectonic activity in the Pontids (Eastern Turkey).

The results of integrated study of the Turonian–Coniacian sediments from the Abinsky district (Northwest Caucasus), which are represented by a rhythmic terrigenous-carbonate sequence, are discussed. The use of microfacial, X-ray diffraction, isotope, and micropaleontological analyses allowed us to reveal important changes in abiotic and biotic evolution during this interval. The peculiarities of carbonate sedimentation, as well as changes in the composition of foraminiferal assemblages, helped to establish fluctuations in the relative sea level, whereas isotopic studies assisted in defining climatic fluctuations. During the periods of accumulation of carbonate and clayey material, the area was occupied by a relatively deep-water open-sea basin with normal salinity. In the background of high temperatures, cooling pulses are also recorded within the studied interval. The position of the Turonian–Coniacian boundary in the section is revised.

An important element in the reconstruction of the geodynamic evolution of the lithosphere in the northwestern Pacific Ocean is the Stalemate Ridge, which is located immediately south of the Aleutian island arc and stretches from southeast to northwest parallel to the Aleutian trench. The collection of our rock samples included rocks dredged along the entire strike of the Stalemate Ridge during cruises 201 and 249 of the German R/V Sonne. This study was focused on peridotites, gabbroids, dolerites, and basalts that fully represent the petrographic diversity of igneous rocks composing segments of the Stalemate Ridge located within a length of 500 km along its strike. The synthesis of all preexisting and newly acquired data on the structure of the Stalemate Ridge and the composition of its rocks led us to the following conclusions of principal importance for developing an adequate geodynamic models for the formation of magmatic complexes and their sources in this area of the northwestern Pacific Ocean: (1) the mafic-ultramafic rock association of the northwestern segment of the Stalemate Ridge was formed at a convergent boundary of lithospheric plates; (2) depleted and enriched sources participated in the formation of magmatic complexes of the Stalemate Ridge; (3) in the area at 170o E within the Stalemate Ridge, a large fault zone occurs, with outcrops of ultramafic rocks found only northwest of this zone and absent southeast of it; and (4) throughout the whole strike of the Stalemate Ridge, magmatic rocks that have no genetic relations to the oceanic lithosphere are sporadically widespread.

Unconventional oil and gas resource development and exploration is the one of the most prospective concept in petroleum geology. High carbon Khadum facies are investigated as unconventional resources in the Precaucas basin and contain gas, gas condensate and oil accumulations. Oligocene and Lower Miocene structure, prospectivity and fields distribution are the one of the most relevant subjects nowadays. This study is focused on the main stages Late Eocene and Early Oligocene deposits formation and the paleogeography of the Khadum formation in the Precaucas oil and gas basin. The new prospective zones are developed in Khadum formation based on the complex analysis of seismic, paleogeography and lithofacies analysis.