The article examines the structure and conditions for the formation of oil and gas bearing Triassic strata in the Caspian region. It has been established that the Scythian and West Turanian plates in the Triassic were located on the active margin of the East European continent. Here a single thick (up to 3–5 km) cover of sedimentary and sedimentary-volcanogenic (mainly tuffaceous) rocks without the characteristic features of rifting was formed. In the north and east of the region, the Triassic is composed of variegated continental terrigenous rocks. In the eastern and southern parts of the Caspian basin, in the Eastern Ciscaucasia, on Mangyshlak, in the Middle Caspian, the Lower Triassic (Olenek) and Middle Triassic are represented by marine terrigenous-carbonate formations. The structural features of the Triassic strata in the Caspian basin are associated with salt tectonics. The maximum thickness (up to 4.5–5 km) of Triassic deposits is developed in the zone of the Paleozoic Donbass-Tuarkyr rift and is caused by the Pre-Jurassic erosion of neighboring territories. The formation of graben-like troughs here is associated with later shear deformations, which is confirmed by their discrepancy with the facies zonation of Triassic deposits. Currently, the Permian and Triassic deposits represent a folded complex, unconformably overlying the pre-Kungurian deposits. Triassic deposits of the Scythian and West Turanian plates are disturbed by faults with an amplitude of up to 2 km, and are dislocated in areas. Folding with faults and strike-slip faults is especially intense on the Karpinsky Ridge. Increased dislocation and Late Triassic magmatism on the Scythian and West Turanian plates are associated with collision processes during the closure of the Paleotethys ocean. Oil and gas prospects are assessed positively.

Both tectonic settings and sedimentary environments of the oil- and gas-bearing Triassic sequences in the Caspian region are examined. It is shown that the Scythian and West Turanian plates were located at an active margin of the East European continent in Triassic. A unified thick (up to 3–5 km) cover of sedimentary and volcanosedimentary (mainly tuffaceous) rocks without the characteristic features of rifting was formed. In the northern and eastern parts of the region, the Triassic is composed of variegated continental terrigenous rocks. In many areas of the region (eastern and southern parts of the Pre-Caspian Basin, Eastern Ciscaucasia, Mangyshlak, and Middle Caspian), the Lower Triassic (Olenekian) and Middle Triassic are represented by marine terrigenous–carbonate rocks. The structural features of sequences in the Pre-Caspian Basin are associated with salt tectonics. The maximum thickness (up to 4.5–5 km) of Triassic rocks within the Scythian Plate is recorded in the southwestern part of the Middle Caspian and southeastern part of the Karpinsky Ridge, where they fill up a series of NW-extending graben-shaped troughs. Their absence in the northwestern part of the region is related to the latest shear deformations, as confirmed by their discrepancy with the facies zonation of Triassic deposits. Currently, the Permian and Triassic deposits represent a pre-platform geodynamic seismic sequence unconformably overlying the pre-Kungurian deposits. Triassic deposits of the Scythian and West Turanian plates are disturbed by faults (amplitude up to 2 km) and dislocated in some areas. Folding with faults and strike-slip faults is especially intense on the Karpinsky Ridge. Increased dislocation and Late Triassic magmatism on the Scythian and West Turanian plates are associated with the processes of collision during the closure of the Paleotethys Ocean. Oil and gas prospects of the region are assessed positively.

The composition and stratigraphy of the evaporite formation in the salt-producing province of the Caspian region are discussed. A seismostratigraphic approach is used for correlation of geological sections in the lateral areas of the salt-producing province with the halokinetically deformed sections in the central areas of the Preсaspian depression. As a result of this research, a new local stratigraphic scheme of the Permian evaporite formation of the Central Subprovince is proposed and the principles of its construction using the results of the seismostratigraphic analysis of the Asselian-Tatarian seismogeological substage and the accepted serial legends of three groups of sheets of geological maps (scale 1 : 1 000 000; Scyphian (South-European), Central-European, and Uralian) are outlined. The results obtained significantly precise the existing schemes of the oil and geological zoning of the Pricaspian oil and gas province and contribute to the development of the resources of the deep (subsalt) horizons of its sedimentary cover.

Research subject. The Zhamanshin structure is located in the northern Aral Sea region and represents the outcrops of pre-Mesozoic rocks among Paleogene deposits. This structure has been known in the literature as a young meteorite crater for more than half a century. Aim. To consider all available geological and geophysical information on the structure and material composition of rocks and explain the development features of the Zhamanshin structure in relation to its position within the Late Paleozoic suture-collision zone of the Eastern-Uralian fold system. Materials and methods. The materials of geological surveys of various scales, as well as the interpretation of geophysical data, satellite images, data on the material composition of rock samples and paleotectonic reconstructions were analysed. In addition, the published literature on the meteorite origin of the Zhamanshin structure was analysed. Results. The main structural features of the Zhamanshin structure are rather associated with the accretion-subduction processes in the Paleozoic and strike-slip movements, especially active in the Pliocene, than with an impact event. The young age of glasses (from 10 thousand to 50 Ma) remains unproven due to unreliable methods used. The composition of the glasses allows them to be attributed to Paleozoic volcanic rocks, while some samples of slags and glasses may be of technogenic origin. Conclusions. Almost all arguments in favour of the meteorite origin of the Zhamanshin structure are questioned. A more realistic conclusion is that it has formed by deep tectonic and geological processes. The Zhamanshin structure is a dissected rounded upland with a ring of Paleozoic rocks along the edges and a hollow in the middle, which is associated with an eroded Carboniferous caldera. After the collision in the middle of the Carboniferous, the entire Northern Aral Sea remained an area of denudation until the beginning of the Cretaceous. After that, terrigenous lacustrine-alluvial strata up to 300 m thick had accumulated. During the Paleogene and Miocene, this upland with the remnants located along a circular rampart tens of meters high was covered by marine and continental sediments. In the Pliocene, the area was subjected to active strikeslip movements with the formation of the Tasaran mega-anticline with the Zhamanshin, North-Zhamanshin and Tasaran uplifts. The Irgiz-Tobolsk shear-thrust had limited and uplifted the western flank of the Zhamanshin structure, while feathering faults resulted in the formation and subsidence of a rounded depression around the Paleozoic caldera in the centre of Zhamanshin.

Research subject. The structure of the pre-Paleozoic deposits and different-age Precambrian basement of the East European platform based on geological and geophysical data. Aim. To trace the evolution of the area under study and to study the geodynamics of processes in order to reconstruct the paleostructure of the Baltica continent. Materials and methods. The current state of the consolidated crust was studied using a geological interpretation of seismic profiling data (transects: “EB-1”, “Tatseys”, “Magnit”) and materials of gravity and geomagnetic surveys. The material composition of the basement rock complexes was studied based on drilling data. Results. The Baltica continent forms the basement of the modern East European Platform. After the Sveconorwegian folding about 1000 Ma, Baltica had become part of the Rodinia supercontinent and merged with the North American platform. A passive continental margin with the Riphean-Vendian sedimentary cover was formed on the eastern Baltica edge. The Petrozavodsk-Khopersky orogen, which arose in the place of the Karelian (Early Proterozoic) Petrozavodsk-Khopersky paleoocean, was reconstructed. The submeridional suture was a result of this paleoocean closure. The orogen structure, as well as that of the paleocontinent Baltica, was disturbed and partially destroyed by subsequent tectonic processes, which continue at the present time with modern rifting. Conclusions. The closure of the Petrozavodsko-Khopersky paleoocean led to the formation of the Baltica continent, which included three microcontinents – Sarmatia, Fennoscandia and Volga- Uralia. Baltica became part of the Rodinia supercontinent during the Sveconorwegian orogeny. Volga-Uralia was located on the border with the PaleoPacific and had a Late Riphean sedimentary cover of the Rodinia supercontinent. This margin underwent destruction during a collision with the Timanides. The scale and extent of the reconstructed Petrozavodsk-Khopersky orogen is comparable to Paleozoic orogenic belts, such as Cadomides, Caledonides, Variscides, or Timanides.

Despite the long history of geological exploration and scientific research in the Caspian region many issues of its oil and gas geological zoning remain controversial, including justification the boundaries of oil and gas provinces at the ancient and young platforms: Pre-Caspian, Ciscaucasia-Mangyshlak and North-Ustyurt. This paper discusses problems of the ancient and young platforms sedimentary cover’s oil and gas zoning using the example of Pre-Caspian region. It is proposed to carry out oil and gas geological zoning of these regions with taking into account the types of the Earth’s crust sections and sedimentary cover’s hydrocarbon systems types, as well as the types of the main oil and gas complexes’ structures. The type of the Earth’s crust section is crucial upon identification oil and gas provinces boundaries; the type of hydrocarbon systems is in the foreground when identifying sub provinces; and the boundaries of oil and gas regions are determined by the main types of oil and gas complexes’ sections and structures. In the Pre-Caspian province three sub-provinces are identified and their oil and gas potential is characterized. The proposed boundaries of the province closely coincide with the distribution contours of the Kungur saliferous strata with considerable thickness (hundreds of meters). Due to the lack of a clear structural boundary between the Paleozoic hydrocarbon systems the Pre-Caspian and Volga-Ural oil and gas provinces are proposed to be considered as a single marginal-continental oil and gas mega-province. The obtained materials and conclusions can serve as a basis for basin modeling and hydrocarbon resources forecast’s refinement.

— The geological and sedimentological interpretation of several time and deep seismic profiles within junction zone of the Volga‒Ural area of the East European Platform, Pre-Caspian Depression, Ural Foredeep, Bashkir Anticlinorium, and northern margin of the Scythian Platform allowed us to identify a number of previously unknown structural features of Later Precambrian and Early Paleozoic formation. On this basis, structural-facies maps were compiled for the Riphean and Vendian stages of development. It was shown that as a result of the collision of the southeastern passive margin of the continent Baltica with Scythia in the Early Vendian and with the Timanides of the Urals in the Later Vendian, a complex tectonic structure of the Orenburg tectonic node was formed, which forms the foundation of the Caspian oil and gas province. The results obtained substantially clarify the structure of the sedimentary cover of the East European Platform and the Pre-Caspian Basin, the stages of the formation and evolution of their structure, and the degree of influence on the sedimentation of structural changes in the adjacent territories of the folded Urals and the Scythian Platform.

The data on the known and assumed subsalt oil and gas prospective structures (traps) of the Pre-Caspian depression are analyzed taking into account the new investigations.Among the major traps are dominated by carbonate (buildups) and terrigenous (fan deep sea deposits) types.A new type of erosion-lithological traps formed during sea level falls was revealed.Large undiscovered traps are located mainly at depths of 6-8 km.The present forecasted resources of hydrocarbons are significantly higher than have been explored ones.

A structural-facies map of the Bashkir stage of the Caspian basin, the southeastern part of the East European platform and the Turan plate is compiled on the basis of drilling data generalization. The sequence of tectonic events and sedimentation processes in the early‒ late Bashkir century of the middle Carboniferous was reconstructed. It is shown that cessation of reef formation, appearance of erosion surfaces and partial destruction of the side ledges of Caspian depression occurred under the influence of Varis orogenesis and the global fall of the World Ocean level due to the glaciation of the Paleogondvana at the turn of early‒middle Carboniferous. It is assumed that oil and gas reservoirs in the rocks of Vise‒Bashkir age are confined to large bodies of carbonate-clastic rocks with clinoform structure that arose on the slopes of the depression due to destruction of its side ledges.

Составлена структурно-фациальная карта башкирского яруса Прикаспийской впадины, юго-восточной части Восточно-Европейской платформы и Туранской плиты на основе обобщения данных бурения. Реконструктуирована последовательность тектонических событий и седиментационных процессов в ранний– поздний башкирский век среднего карбона. Показано, что прекращение рифообразования, возникновение поверхностей размыва и частичное разрушение бортовых уступов Прикаспийской впадины произошло под влиянием варисского орогенеза и глобального падения уровня мирового океана из-за оледенения Палеогондваны на рубеже раннего и среднего карбона. Предполагается, что разервуары нефти и газа в породах визе-башкирского возраста приурочены к крупным телам карбонатно-обломочных пород клиноформного строения, возникших на склонах впадины за счет разрушения ее бортовых уступов.

The Karatau–Talas–Ferghana Fault (KTF) extending for 1500 km from Turgai to western Tarim is one of the world’s largest intracontinental strike-slip faults. This paper overviews the evolution of the KTF, providing insight into its relatively poorly studied northern segment in the Karatau Range and Turgai, known as the Main Karatau Fault (MKF). The right-lateral strike-slip along the KTF developed during three stages in the late Permian–Triassic, Early–Middle Jurassic, and late Cenozoic. The total strike-slip decreases northward from 200 km in the Ferghana Range to 100 km in the Karatau Range and decreases to zero in southern Turgai. Kinematic analysis of Jurassic grabens compensating the strike-slip in southern Turgai shows that strike slip along the KTF in the Jurassic, previously regarded as insignificant, actually measures tens of kilometers and 50% of the total strike slip in the northern segment of this fault.

ОСОБЕННОСТИ СТРОЕНИЯ ПАЛЕОЗОЙСКИХ ОТЛОЖЕНИЙ ТУРГАЙСКО-СЫРДАРЬИНСКОГО И УСТЮРТСКОГО РЕГИОНОВ (В СВЯЗИ С ПЕРСПЕКТИВАМИ НЕФТЕГАЗОНОСНОСТИ ГЛУБОКИХ ГОРИЗОНТОВ ОСАДОЧНОГО ЧЕХЛА

The correlation of geological events and structure-forming processes occurring contemporaneously in the inner parts of cratons and the adjacent paleooceanic basins is discussed in order to understand the effects of these processes on sedimentation and structural rearrangements. For this purpose, a series of paleodynamic reconstructions of the Riphean, Vendian, and Paleozoic epicontinental basins of the East European Platform and zones of their transition to marginal basins of the same age once situated in the Ural, Timan, Caucasus, Scandinavian fold regions and in the Scythian-Turan Plate have been performed on the basis of the available original and published data combined with interpretation of seismic profiles. As a result, a set of structural-facies maps of this territory have been compiled for several time intervals from the Late Riphean to Early Permian.

Статья посвящена корреляции геологических событий и структурообразующих процессов, происходящих одновременно во внутренних частях кратонов и смежных палеоокеанических бассейнах, оценке влияния этих процессов на осадконакопление и структурные преобразования. Для решения этой проблемы на основе обобщения имеющихся оригинальных и опубликованных данных и материалов сейсмопрофилирования выполнена серия палеогеодинамических реконструкций рифейских, вендских и палеозойских эпиконтинентальных бассейнов Восточно-Европейской платформы и зоны их перехода к окраинным бассейнам соответствующего возраста, некогда располагавшихся на месте Уральской, Тиманской, Кавказской и Скандинавской складчатых областей и Скифско-Туранской плиты. В результате составлена серия структурно-фациальных карт этой территории, охватывающих период времени с позднего рифея до ранней перми.

Analysis of available published geological-geophysical data by the new seismic data CDP and drilling allowed making a conclusion that there are two groups spatially separated salt dome structures within the Chu-Sarysu basin. Age of rocks in the cores of the Permian salt structures in the north-west and the Devonian in the southeast, and not only the Devonian as previously thought. The shear-thrust movements are the decisive role in the development history of the Permian salt domes in northwestern Chu-Sarysu basin.

Analysis of available published geological-geophysical data by the new seismic data CDP and drilling allowed making a conclusion that there are two groups spatially separated salt dome structures within the Chu-Sarysu basin. Age of rocks in the cores of the Permian salt structures in the north-west and the Devonian in the southeast, and not only the Devonian as previously thought. The shear-thrust movements are the decisive role in the development history of the Permian salt domes in northwestern Chu-Sarysu basin.

Seismostratigraphic analysis of Paleogene deposits in northeastern Ustyurt was carried out. Four seismostratigraphic complexes have been recognized: Paleocene–Ypresian, Lutetian–Bartonian (Tasaran unit), Bartonian–Priabonian (Saksaul’skaya–Chegan), and Oligocene. We have established for the first time the clinoform structure of the Tasaran and Saksaul’skaya–Chegan complexes, which explains various concepts of their age. Seismostratigraphic analysis must be an integral part of stratigraphic research, which will significantly increase the reliability of correlation between geological sequences.