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The early stages of basic-ultrabasic magmatism in Sarmatia are characterized by the appearance of ultrabasic rocks formed from the mantle with an abnormally high iron content. Therefore, it is important to study them as the source of information about the stages and causes of the activity of the mantle and its possible composition. This magmatism has been recorded in Sarmatia since the beginning of the Eoarchean. The relics of Eo- and Paleoarchean basic and ultrabasic rocks were found in the Dniester-Bug, Kursk, and Azov provinces, which underwent tectonic reconstruction in the Mesoarchean and Paleoproterozoic. Mesoarchean basic-ultrabasic magmatism is manifested in all provinces of Sarmatia and is represented by effusive and intrusive facies. The Mesoarchean greenstone belts composed of komatiites and basalts have been well preserved in the Middle Dnieper province; in other provinces, they are strongly deformed and form narrow linear structures. The Paleoproterozoic endogenous activity in Sarmatia differs from that in other regions in the almost complete absence of magmatism in the period 2.5-2.3 Ga and its significant manifestation 2.1-2.0 Ga. The magmatism in Sarmatia at this stage is similar in the ratios of basic-ultrabasic and granitoid complexes to the magmatism in South Africa but differs from that in Fennoscandia and Canada: The volume of granitoids coeval with basic rocks is larger than the volume of mantle magmatism. The igneous complexes formed 2.1-2.0 Ga in Sarmatia and South Africa are also similar in the presence of norites, the enrichment in Ni and platinum group elements, and the ratio of granitoids and basic-ultrabasic rocks. Magmatic activity (first of all, basic-ultrabasic magmatism in ancient cratons) is not a synchronous phenomenon on a planetary scale and varies greatly in the volume of produced material within the same time intervals. Early Precambrian basic-ultrabasic rocks (volcanics of greenstone belts, intrusions of large igneous provinces, and layered massifs) resulted from plumes, whose derivates formed within the lower and upper mantle and/or the upper mantle and crust, which determined the heterogeneous composition of igneous rocks. The spatial heterogeneity and nonsynchronic occurrence of basic-ultrabasic magmatism might have been due to impact events serving as the triggers of plumes.

The paper considers the geologic structure of the region and the current problems and prospects for the development of its energy potential and environmental safety. We provide grounds for the necessity of integrated projects aimed at studying the deep structure of the Caspian region as a single object by its five coastal states: Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan. The proposed Geokhazar project is aimed at obtaining the lacking parametric geological and geophysical information about the deep subsurface structure of the water area of a sedimentary basin in the unique intracontinental catchment of the Earth. The project provides for the development of a universal prospecting concept taking into account the emplacement and conservation of hydrocarbon fields under severe thermobaric conditions at great depths and the absence of regionally consistent drainage systems; the determination of the factors influencing the nature of long- and medium-frequency eustatic fluctuations in the Caspian Sea level; and the assessment of the energy (geothermal and hydrocarbon) resources of the deep subsurface in the Caspian, cis-Caucasian-Mangyshlak, and South Caspian oil and gas provinces.

The Hercynian mobile belts in Central Asia include the proper Hercynian and Late Hercynian (Indo-Sinian) belts, whose formation is associated with the evolution of the South and Inner Mongolian basins with oceanic crust. Within the South Altai metamorphic belt (SAMB), rock complexes compose tectonic slivers of different ranks. At the early stages, their metamorphic alteration occurred under conditions of the high-temperature subfacies of the amphibolite and, in places, granulite facies. Structurally, the band of the outcrop of these complexes is confined to the Caledonian North Asian continental margin and stretches along the southern slope of the Gobi-Mongolian-Chinese Altay Mountains from southeast to northwest (East Kazakhstan), where they occur in the Irtysh strike-slip zone. We assign these complexes to the Hercynian SAMB, running for more than 1500 km. The latter comprises poly- and monometamorphic complexes. Late metamorphic granitoids of the Tseel tectonic plate (Gobi Altay) in the southeast of the SAMB have been dated at 374 ± 2 and 360 ± 5 Ma. The previous data and these results show that the early (~390-385 Ma) low-pressure and late (375-360 Ma) high-pressure metamorphism proceeded almost along the entire belt. The interval between them was a short tectonic lull. These processes took place during the closure of a Tethyan basin of the South Mongolian Ocean (Paleo-Tethys I). The spatial position of the SAMB was controlled by the structural asymmetry of the basin, with an active continental margin at its northern edge and a passive one at the southern edge (in the present-day coordinates).

We substantiate certain ideas concerning the key role of fluid-geodynamic processes in the evolvement of hydrocarbon accumulations at great depths in the Earth’s crust. The presented geodynamic model of oil and gas accumulation is based on updated ideas of the structure of the Earth’s tectosphere, which includes plate, preplate, and folded complexes. The model makes clearer the spatial scale of the organic-matter transformation into hydrocarbons of the oil series. In the bottom layers of the Earth’s crust, we predict the existence of a special stagnation type of water drive systems with the following distinguishing features: (a) different scales of manifestation, from local to regional; (b) a limited water exchange with the external environment; (c) the absence of persistent drainage horizons (beds and interbeds); (d) alignment of hydrodynamic potentials in terms of depths and laterals; (e) certain growth in the role of lithohydrochemical and organic chemical factors in the development of the void space of the fluid-host medium. In their inner space, systems with difficult water exchange can control the evolvement and preservation of autoclave hydrocarbon systems for a long time, the key feature of the autoclave systems being spatial coincidence (localization) of the processes of oil and gas generation and accumulation. We assume that in the settings of all-round compression, hydrodynamic instability, and no drainage, the position of productive zones must be controlled by foci of low pore (reservoir) pressures rather than local hypsometric highs. We present results of the prediction for the development of water drive stagnation systems in the subsalt deposits of the Caspian depression. A prediction for reservoir pressures was made for the sedimentary cover at great (and supergreat) depths. It can be regarded as a necessary component of prediction of oil and gas potential because it makes it possible to delineate new (previously unknown) commercial zones of hydrocarbon accumulation.

The Vendian deposits of the Siberian Platform are represented by four regional horizons (from bottom to top): Nepa, Vilyuchan, Tira, and Danilovka. The TDS of brines in the Nepa and Vilyuchan horizons varies from 170.3 to 470.1 g/L³, and the TDS in the overlying Tira and Danilovka horizons, from 84.6 to 583.1 g/L³. Brines of Cl Na, ClNa-Ca, Cl Ca-Na, Cl Ca, and Cl Ca-Mg types have been identified. The pH values of the brines vary from 3.0 to 7.0; acidic and weakly acidic brines (pH = 3.0-5.5) prevail. The redox potential Eh varies from -440 mV (highly reducing conditions) to +130 mV (oxidizing conditions), averaging -176 mV. Areal regional hydrogeochemical zoning is controlled by the outer (on the periphery of the Siberian Platform, where infiltration of meteoric waters took place) and inner feeding areas. The outer feeding areas bear infiltrogenic brines of different ages (group I), mostly of Cl-Na composition. They are characterized by TDS ≤ 280 g/L³, r Na/ r Cl ≤ 1.55, Cl/Br ≤ 2512, and average Ca/Cl = 0.3. The average values of the integrated brine metamorphization index S (according to S.L. Shvartsev) range from 50 to 200. In the intraplatform feeding areas, there are several phases of brines that underwent gravitational sinking into the Vendian horizons in the periods when Cambrian salt-bearing basins existed on the platform. These brines were metamorphosed during filtration along the fracture and fault zones. The intrusion of traps in the late Permian-early Triassic was accompanied by hydrothermal activity. The waters of the enclosing Cambrian dolomite horizons were heated to 800-1000 ºC; their subsequent interaction with carbonate rocks and evaporites (in particular, chlorides) resulted in extrastrong saturated brines. These brines were also subjected to gravitational sinking into the Vendian reservoirs, which was the main cause of the inverse vertical hydrogeochemical zoning in the hydrogeologic subsalt formation. The brine metamorphism processes and temperature changes in the rock horizons during the intrusion of traps and their subsequent cooling led to a significant alteration of the enclosing rocks under interaction with brines and to salinization of the reservoirs, an increase in the total salinity of the brines, and catagenetic changes in their composition. The brines closest to the maximum saturation with halite were found in reservoir zones with the highest salinization and near faults and boundaries of intrusive bodies. During the pre-Vilyuchan, pre-Dnieper, pre-Tira, and pre-Danilovka sedimentation breaks, infiltrogenic waters penetrated into the Vendian sediments. Geochemically, the sedimentogenic, infiltrogenic, and metamorphic strong brines (group II) have a predominantly Cl-Ca or Cl-Ca-Mg composition with TDS > 350 g/L³. They are characterized by low r Na/ r Cl ratios (on average, 0.3), Cl/Br ≤ 100, high Ca/Cl values (on average, 0.4), and S > 250.

The general Vendian stratigraphic scale of Siberia, with the uncertain age of the Vendian base ranging from 600 to 630-640 Ma in most of recent publications, remains worse constrained than the Cambrian scale, in which the boundaries of epochs and stages have been well defined. However, the imperfect classical stratigraphic division has been compensated by data on the cyclicity of the Vendian-Cambrian sedimentary section. The Vendian stratigraphy of the Siberian Platform and the related deposition history with cycles of sedimentation and gaps, as well as the hierarchy of sedimentation processes, can be inferred from the succession of alternating clastic, carbonate, and salt units. The cyclicity of geologic processes and their recurrence are attributed to periodic oscillatory motions of the crust. The ranks of these motions correlate with the cyclicity of sedimentary strata, including regocyclites, nexocyclites, and halcyclites separated by gaps. Each Vendian long-period oscillatory motion begins with a regocyclite and ends with a regional-scale gap. The Cambrian section includes one pre-Mayan regional gap at the end of the early Cambrian long-period cycle. Cambrian regocyclites are composed of carbonate subformations and formations in the lower part and alternating salt and carbonate beds in the upper part.

We present a model of the stratigraphic and lateral distribution of Cambrian deposits in the Vilyui hemisyneclise, based on an analysis of drilling data and interpretation of seismic data. The study shows a series of formations and sequences penetrated by wells (Syugdzher saddle, Khorgochum monocline, Ygyatta depression, Tyukyan-Chybyda monocline, Arbai-Sinyaya megaswell, etc.). In the areas where the Cambrian was not penetrated by wells, the distribution of Cambrian deposit was inferred based on the available seismic data. The distribution of the Kuonamka Horizon formed by Cambrian organic-rich rocks is characterized in detail. These are the Kumakh and Sinyaya-Kutorgina sequences and the Inikan and Kuonamka formations. It has been found that the Kuonamka Horizon was deposited during two stages, Botomian and Toyonian-early Mayan. The horizon is overlain by younger deposits of the Mayan Stage, with characteristic cross-bedding structures. Schemes of facies zoning of the Cambrian for Botomian, Toyonian-early Mayan, and middle Mayan times were constructed based on the most recent geological and geophysical understanding of the Vilyui hemisyneclise.

The paper considers the regularities in the structure and conditions of formation of Domanik carbonaceous carbonate-siliceous productive deposits. They are shown to occur in the stratigraphic interval from middle Frasnian to upper Famennian. The highly persistent structure of their sections for many kilometers within specific sedimentation zones and the drastic changes in the structure at the boundaries of the zones are justified. Lithological classification of rocks is considered. Methods and results of combined paleontological, lithological, geochemical, and petrophysical core studies are presented, as well as interpretation of well logging data and seismic-survey materials used in the assessment of oil resources and identification of oil- and gas-promising zones and areas. The conducted studies have proved significant oil resources in the Domanik productive sequence; their extraction might compensate for the decline in oil production from conventional pools.

The paper considers the seismogeologic, structural, and tectonic features of Neoproterozoic-Paleozoic and Mesozoic sedimentary complexes in the Arctic regions of the Siberian Platform. Based on the results of deep drilling, the geologic structure of the study area was analyzed, and the key sections of Neoproterozoic-Paleozoic deposits of the Anabar-Khatanga and Lena-Anabar oil and gas areas (OGA) were compiled. Analysis of geological and geophysical materials showed the existence of a sedimentary basin up to 14-16 km in thickness on the continental margin of the Siberian Platform, with five regional seismogeologic megacomplexes in its section: Riphean, Vendian, lower-middle Paleozoic, Permian, and Mesozoic. Based on the results of a complex interpretation of CDP seismic-survey and deep-drilling data, a structural and tectonic analysis was performed, structural maps were compiled for all reference stratigraphic levels, and a conclusion has been drawn about the similarity of the structural plans of the Riphean top and overlying sedimentary complexes. Using a structural map along the Permian top, a tectonic map of the study area was compiled, which corresponds to the current state of study. The results of numerical modeling of the salt diapir formation processes are presented, and the types of anticlinal structures, potential oil- and gas-promising objects, are considered.

The paper presents results of regional paleogeographic reconstructions of the West Siberian sedimentary basin in the Late Bajocian-Bathonian. Regional paleogeographic maps of the Yu₄, Yu₃ and upper part of the Yu₂ reservoir units were constructed and described for the first time ever. The implemented approach provided insights into the evolution of paleolandscapes and highlighted the deposition features of the Upper Tyumen Subformation and Malyshev Formation in the different parts of the West Siberian basin. The compilation of paleogeographic maps was based on the electrofacies analysis performed for individual parts of the Malyshev stratigraphic horizon, with regard to the core description materials, paleontological, sedimentological, geochemical data and other. The paleogeographic control of the reservoir’s formation in the Bathonian regional reservoir is discussed.