East European Platform Research Articles

ON THE TIME AND CONDITIONS OF FORMATION OF THE SHOKSHA QUARTZITE-SANDSTONES OF THE SOUTH ONEGA DEPRESSION BASED ON THE NEW DATA FROM ISOTOPE GEOCHRONOLOGY

The first results of U-Pb isotope dating of detrital zircons (dZr) from red-colored quartzitic-sandstones of the Shoksha formation (Shoksha horizon) are presented. The Shoksha formation completes the Vepsian sub-horizon (Vepsian) of the Lower Proterozoic of Karelia and is distributed within the South Onega trough. A sample (KL-555) of red-colored quartzitic sandstones was taken from the lower part of the section of the Shoksha formation in the same name deposit within the southwestern Cis-Onega Lake region. The 79 dZr grains isolated from this sample were analyzed by the staff of the Chemistry-Isotopic Analytic Laboratory of the GIN RAS using the equipment of the Shared Research Facilities of the GIN RAS. The weighted average of the three youngest U-Pb isotope dates for dZr grains is 1906±13 Ma. Taking into account the known isotopic dates of gabbro-dolerites from the Ropruchei sill, that cuts through the Shoksha formation, it makes possible to constrain the time of the Shoksha formation accumulation by ~1.90–1.75 Ga. A significant part of the carried out analyzes has yielded a high degree of discordance of the dates. The features of the distribution of the figurative points of these analyzes in the diagram with concordia suggest that the rocks of the studied section of the Shoksha formation were subjected to the alteration that disturbed the U-Pb isotope system of these zircon grains in the Phanerozoic.The set of obtained dates for dZr grains has been compared with the known ages of the crystalline complexes of the basement of the East European Platform. The age sets of dZr grains from sample KL-555 and rocks of the Ladoga group, developed along the margin of the Svecofennian accretionary orogen, are very similar (p similarity coefficient in Kolmogorov – Smirnov test is 0.27) and characterize mainly tectonic–magmatic events that had immediately preceded the manifestation of the Svecofennian orogeny (1.9–1.87 Ga). Therefore, the rocks of the Ladoga group could highly probably be a secondary source for the Shoksha quartzites. Based on a comparative analysis of ages and thorium-uranium ratios (Th/U) in dZr grains from sample KL-555, it was concluded that some of the studied dZr grains with high Th/U>1.5 originate from Ludicovian mafic rocks, but those with low Th/U<0.1 originate from ultra-high-pressure formations, such as eclogites known in the Salma, Kuru-Vaara and Gridino.A paleo-geographic scheme for the Late Vepsian is proposed, showing that the highly mature Shoksha sandstones were generated under continental conditions in a local basin due to the accumulation of clastic material carried by an extensive and branched

Fault systems in multiply deformed regions of Eurasia

We have studied the orogenic fragile deformation of the upper Earth's crust of several areas of the Eurasian continent, where deformations have occurred many times -- in the Tian Shan and Altai-Sayan regions of the Central Asian Paleozoic Fold Belt and in the Baltic region in the Fennoscandian Shield (East European Platform). Our processing of data on the trends of more than 4000 faults allows us to identify fault systems and relationships among these fault systems. Changes in the intensity and kinematics of the activity of fault systems in different epochs of deformation of regions are revealed. In the Tien Shan and Altai-Sayan regions, fault movements occurred during Early Paleozoic, Late Paleozoic and Late Cenozoic orogenies. No new fault systems appeared in the Late Cenozoic deformation in the Tien Shan, where only movement along Paleozoic faults that were suitably oriented occurred. In the Altai-Sayan region, we identify the Late Paleozoic associations of fault systems that activated in the recent epoch and the association of fault systems created in the Late Cenozoic. The Fennoscandian Shield shows different fault kinematics in four Early Proterozoic deformational periods. Our method of analysis of associations of fault systems contributes to a~systematization of data on multi-stage deformation in the upper crust of these regions.

The role of the Semiluky-Lipetsky Fault in the recent structure of the eastern slope of the Voronezh uplift

One of the discontinuous faults in the south of the East European Platform — the Semiluki-Lipetsk fault along the border of the Voronezh newest uplift and the Oka-Don trough. Detailed studies using the methods of engineering-geological, geophysical, geodesic, geochemical, structural-geomorphological, etc., accompanied by drilling and field studies, allowed us to determine the type of discontinuity as a extension with the participation of right-strike-slip (dextral shear) stresses. It is associated with fracturing of bedrock and Quaternary sediments, landslides and falls, including large gravitational-tectonic massifs, surface and underground karst, suffusion, and pull-apart depressions. In general, these processes and phenomena affect the geological stability of the site of the nuclear power plant, causing the development of negative processes. The reasons for the extension conditions in the Semiluki-Lipetsk fault zone are considered from two positions — the influence of pressure from the south from the Alpine orogen of the Caucasus and the connection with intra-platform deep processes that cause the extension the earth’s crust under the Oka-Don trough.

The conodont biofacies model of shallow paleoenvironments in Frasnian (Late Devonian)

The article considers various criteria of the conodont biofacies distinguishing, and principles of conodont paleoecological models reconstructing. The proposed conodont biofacies model is based on conodont distribution in the Frasnian (Upper Devonian) of the Voronezh anteclise (Central regions of Russian Platform).

The Possible Consequences of the Technogenic Seismic Impact on the Geological Environment in the Central Part of the East European Platform Based on Data from the Small-Aperture Mikhnevo Seismic Group

The Possible Consequences of the Technogenic Seismic Impact on the Geological Environment in the Central Part of the East European Platform Based on Data from the Small-Aperture Mikhnevo Seismic Group

Геолого-геофизические исследования кольцевых геоморфологических структур на территории юга Русской платформы и перспективы поисков месторождений нефти и газа

The use of regional geological and geophysical research methods in the geological and morphological mapping of areas significantly increases the information content and efficiency of predictive exploration of oil and gas research. Aim. To show the possibilities of regional geological and geophysical research methods for studying the morphological concentric features of the tectonic structure and the search for oil and gas deposits within the south regions of the Russian Platform and Caucasus. Methods of research. Various geological and geophysical methods (analysis data of decoding satellite images, of heat flow data) were used. Results of research. The paper revealed the presence of a certain spatial mutual correlational relationship in the location of oil and gas fields in the southern regions of the Russian Platform and Caucasus regions with the location of geomorphological structures of the central type according to the data of decoding satellite images and surveys of heat flow measurements, in the form of ring (sometimes elliptical, spiral) structures. For the first time, the peripheral spatial location (in the side zones) of the main oil, gas, and bitumen deposits relative to the central part of the paleomantle plumes in the southern regions of the Russian Platform, forming geological and morphological structures of the central type, similar to the Pre -Caspian ring morphological structure, where a significant number of oil and gas fields are also concentrated in the southern regions of Russia, is revealed. It is revealed that high values of the heat flow determine the high productivity of oil and gas fields located within the geomorphological structures of the central type. The results of the prognostic assessment in the southern regions of Russia are shown, in order to identify areas that are promising for the search for new oil and gas deposits.

U-Pb (LA-SF-ICP-MS) dating and probable provenance of detrital zircons from terrigenous deposits of the Upper Precambrian of the Subpolar Urals

Research subject. Upper Precambrian metaterrigenous deposits of the northern part of the Lyapinsky anticlinorium in the Subpolar Urals.Material and methods. From the metaterrigenous rocks of the Upper Precambrian section of different stratigraphic levels, monofractions of zircons were isolated and their optical and isotope-geochronological (U-Pb LA-SF-ICPMS) studies were performed.Results. Age boundaries of the formation of the Puivinskaya, Khobeinskaya, and Moroinskaya Formations in the Subpolar Urals were specified. A comparison was carried out of age populations of detrital zircons from metaterrigenous deposits of the Subpolar Urals and terrigenous sequences of adjacent regions similar in age. The age boundaries and the proposed location of crystalline complexes, the probable provenance areas of terrigenous material, were established.Conclusions. The lower age limit of the formation of the basal layers of the Upper Precambrian of the Subpolar Urals does not go beyond the Late Riphean. The north-eastern periphery of the East European Platform, including the Subpolar Urals, in the Late Precambrian belonged to the same continental margin, and the accumulation of the Middle-North Timan and Subpolar Ural Upper Riphean sediments occurred in the common sedimentation basin. The lower age boundary of the formation of the Puivinskaya Formation (about 1000 Ma) determines the probable formation time of the Timan passive margin.

EXPERIENCE IN GEOSTRUCTURAL AND GEODYNAMIC INVESTIGATIONS OF NUCLEAR POWER PLANT ALLOCATION TERRITORIES FOR ASSESSING STABILITY OF ENGINEERING STRUCTURES

The results of geological and structural-geodynamic research are presented for the territories of several nuclear power plants (NPP) located on the East European Platform. The influence of geological structure, lithology, and the latest tectonic movements are considered as well as the resultant structures and relief, which generally represent the geological environment, on the stability of the NPP areas. Structural and geodynamic conditions, in particular, recent tensile stresses that cause intense rock fracturing and high gas-fluid permeability, suffusion, karst and landslide, are proved to be the main causes of hazardous processes resulting in settling and tilting of some NPP buildings. Tectonic sloping of the sites towards descending depressions, the sand basement of NPP sites, sloping clay aquicludes, fluctuating water levels in the adjacent water reservoirs, the presence of so-called “hydrogeological windows”, the buried relief and modern structural and geodynamic conditions, i.e., tectonic stresses (tensile stresses in many cases) contribute to building deformations. Along with solving practical problems, a number of theoretical issues are considered. Lineaments are associated with rock fracture zones and faults zones; the fault zones in crystalline foundation influence the formation of recent structures; and new platform structures, i.e. gravity-tectonic massifs and pull-apart depressions, are distinguished.

Mantle gravitational anomalies in the regions of Eurasia, North America and the Atlantic

The construction of density models of the Earth's crust and upper mantle along the system of profiles crossing Eurasia and North America, the Atlantic Ocean, and transition zones between continents and oceans, begun by the works of the authors of recent years, is continued. In the crust, they are plotted by velocity sections along DSS profiles. The calculated effect of the section in anomalous densities in relation to the normal platform mantle (minus 870 mGl) corresponds to the zero observed field (Bouguer anomalies on land and Fay anomalies on sea). This value is established experimentally on the East European platform, where the geological and geophysical knowledge is the maximum. In the upper mantle, the authors' ideas about deep processes are used. They are associated with variants of heat and mass transfer under various endogenous regimes. Based on the results of these processes, temperature distribution that distinguish the densities of mantle rocks in each region from platform ones was determined. The gravitational effects calculated for such anomalous models are summarized with the crustal ones. Regions with all types of endogenous regimes were studied: platforms, zones of recent activation, geosynclines and rifts of different ages, mid-ocean ridge, oceanic depressions, marginal trench, island arc, back-arc depression. The total has compared with the observed fields. In all previously studied regions, the obtained differences do not exceed those explained by the errors of observations and calculations. Thus, the construction of density models of the tectonosphere becomes one of the methods for verifying the used schemes of deep processes. In the regions covered by recent activation and in the transition zones between continents and oceans, the differences between the experimental and calculated data turned out to be the maximum. Therefore, the work was continued using other DSS profiles, mainly on the continental platforms. The result generally confirmed the previous one, revealing additional modeling problems associated with velocity cross sections of the earth's crust.

Morphology, Structure, and Composition of Zircon from Metasandstones of the Alkesvozhskaya Sequence (Polar Urals)

A description of the features of morphology, internal structure, and analysis results of Th/U and Zr/Hf ratios in zircons from sandstones of the gold-bearing Alkesvozhskaya sequence, located at the basement of the Paleozoic section in the Subpolar Urals, is presented. It has been established that most of the studied zircons are primary igneous grains of the first weathering cycle. The detrital zircon source was probably in formations close in age, underlying or located nearby felsic and basic volcanics of igneous complexes of different stages of formation of Timanides-protouralides, associated granitoids, and intrusive mafic formations. Small part of well-rounded zircon Pre-Riphean grains can be redeposited from the Riphean metasedimentary formations, which, in turn, inherited it from the rocks of the ancient basement of the East European Platform.

Structural position and some features of the geological structure and the development of the Black Sea Depression

The structural position of the Black Sea deep-sea depression is generally determined by its location in the area of intersection of diagonal transcontinental tectonolineament belts. The different thickness of deposits of the same age in different depressions emphasizes the bloc structure of the earth's crust in the water area. Space photographs clearly show the contours of the depression are enveloping by the long arcs of the mountain ranges and valleys of the Caucasus, Ajaro-Trialetia, and the Eastern and Western Pontides. Such large oval and arcuate, partially sequentially superimposed structures (the Miesian plate, Pannonian and Bohemian massifs) are characteristic of the entire southeastern border of the East European platform and reflect the activity of the processes of destruction of its southern foreland in the zone of development of the classic geosyncline. The available data allow us to assume the superimposed nature of the Black Sea depression, formed as a result of mainly vertical tectonic movements in the field of development of mantle plume activations.

SEISMICITY of the RUSSIAN PART of EAST EUROPEAN PLATFORM and ADJACENT TERRITORIES in 2016–2017

Seismic observations by 46 stationary seismic stations, including seven temporary seismic stations located in the area of Novovoronezh and Kursk nuclear power plants, and by two arrays were carried out on the Russian territory of the East European Platform. A feature of seismicity in 2016–2017 is a manifestation of swarms of weak earthquakes in the northwest in the Leningrad region and the adjacent territory of Finland, as well as earthquakes on the Ukrainian Shield with Мs(est.)=3.8 in Krivoy Rog, where mass explosions are carried out in mines, but earthquakes of moderate magnitude МL=2.6–3.9 also occur (2007, 2013). Weak earthquakes in the peripheral parts (in the southwest, west and northwest) and in zones associated with paleorift structures: in the northeast – with the Kirov-Kazhim and Central Russian aulacogenes continue to be recorded. Weaker natural seismicity with ML≤2.5 was recorded in Karelia and the regions bordering Finland, near the Kandalaksha Bay, near the Khibiny and Lovozero massifs on the Kola Peninsula and in the territory of the Voronezh crystalline massif.

MARIUPOL EARTHQUAKE on August 7, 2016 with Мw=4.6, I0=5 on the NORTHWESTERN COAST of the SEA of AZOV

The instrumental and macroseismic data on the earthquake of August 7, 2016 with Mw=4.6, which occurred near the city of Mariupol (Ukraine) and was felt in 47 settlements at distances up to 458 km from the epicenter with an intensity of 2 to 5 at MSK-64 scale , are presented. The earthquake occurred in the area of the North Azov fault at the southern border of the East European platform. The spatial distribution of macroseismic data made it possible to construct a map of isoseists of Ii=3 and 4. The focal mechanism is constructed and a strike-slip motion type in the focus is determined.

К вопросу о геологической природе неоднородностей кристаллического фундамента Восточно-Европейской платформы

Based on the analysis of gravitational and magnetic anomalies of the eastern part of the East European Platform, it is concluded that inhomogeneities caused by serpentinization processes are present in the Earth’s crust. This conclusion is confirmed by conducting geological and geophysical studies on reference objects with serpentinite outcrops.

PROVENANCE AND AGE CONSTRAINTS OF THE RIPHEAN SANDSTONES FROM THE IVANOVSKY GRABEN (THE KOLA PENINSULA) BASED ON THE U-Pb LA-ICP-MS DATING AND RAMAN SPECTROSCOPY OF DETRITAL ZIRCON

The results of U-Pb LA-ICP-MS dating of 150 detrital zircon grains from the Precambrian (Riphean?) sandstones of the Kildin group on the coast of the Ivanovka Bay (northeastern Kola Peninsula) are presented. A group of three youngest grains yielded constraint on the sandstone maximum depositional age of 1179±45 Ma. Detrital zircon age distribution is dominated by three maximums of 1.9, 2.4 and 2.7 Ga. The authors consider two complementary scenarios of interpretation of the data obtained. The first scenario involves the contribution of distant provenance out of granitoids in the Lapland-Kola orogen (~1.9 Ga) and adjacent areas of the Kola-Karelia region (~2.7 Ga), Imandra-Varzuga structure (~2.4 Ga), and Sveconorwegian belt (~1.2 Ga); the off-Baltic (Greenland?) sources of the detrital zircon also cannot be excluded. According to the second scenario, the Ivanovsky graben received zircons also from the proximal sources – sialic complexes formed upon melting of granite-gneiss substratum of the upper crust of the Murmansk craton during largescale episodic mafic magmatism 1.86, 2.50 and 2.68 Ga. The Raman spectroscopy showed that about 25 % of the analyzed detrital zircon grains experienced a 1.4-Ga-old thermal effect which did not lead to Pb losses but partially restored the crystalline structure of zircon. This result can be used as an additional constraint in the detailed provenance analysis of the northeastern East European Platform sedimentary basins and is indicative of 1.4-Ga-old large-scale magmatic events related to the breakup of the supercontinent Nuna.

The role of the Absheron facies in the formation of the productive strata in the South Caspian Basin

In oilfield practice, the lithofacies criterion is very often decisive for the formation of deposits of liquid and gaseous hydrocarbons. The Absheron lithofacies type of sediments (Absheron facies), enriched in quartz material, composes the reservoirs of the horizons of all large oil and gas fields in the South Caspian Basin. The genesis of the Absheron facies is closely related to the genesis of the productive stratum, there is no consensus on both issues to date. It is indisputable that the productive stratum and the Absheron facies were formed in the conditions of a closed continental basin, which arose as a result of the orogenic restructuring of the areas surrounding the Caspian Sea, the bowing of its bottom and the subsequent Pontian regression of the sea. As a result of the restructuring of the hydrographic system in the south of the Russian Platform, many paleorivers, flowing along the newly formed land, began to flow and carry a huge amount of water and precipitation into the South Caspian Basin. Deposition of the productive stratum and Absheron facies began. The greatest role in the supply of quartz-enriched sandy material belonged to the Paleovolga, which, together with other paleorivers in the north of the South Caspian Basin, formed an extensive marginal delta, from which sediments were transported far to the south, west, and east.

Paleontological Characteristics of the Upper Vendian–Lower Cambrian Sediments in the Section of the North Polotsk Borehole of the East European Platform, Belarus

Paleontological Characteristics of the Upper Vendian–Lower Cambrian Sediments in the Section of the North Polotsk Borehole of the East European Platform, Belarus

Dinoflagellate cyst and nannoplankton assemblages from the Middle Eocene Kuma Formation of Crimean Peninsula — biostratigraphy and palynofacies

The stratigraphic correlation of the Kuma Formation from the south of the Russian Platform and the Crimea-Caucasian region has been a matter of debate for decades. A bed-by-beds study of dinocysts and nannoplankton from the the Kuma Formation made it possible to recognize a sequence of biotic events, important for defining and correlating the biozones. At the Bakhchisarai limestone quarry, six dinoflagellate zones and six nannoplankton zonal units were recognized, assignable to the Middle Eocene Lutetian and Bartonian stages. Our paleoecological analyses of the organic-walled microphytoplankton assemblages and of the palynofacies indicate that the the Kuma Formation deposited in the inner shelf zone, probably of anoxic and eutrophic settings within the Pontic-Transcaucasian magmatic belt. Assemblages of organic-walled microphytoplankton comprise potentially toxic dinoflagellate species of Alexandrium. The Middle Eocene Climatic Optimum event is recorded in the upper part of the the Kuma Formation, presumably indicated by the Dracodinium rhomboideum dinoflagellate zone, which is characterized by an acme of Dracodinium laszczynskii Gedl and the lowest occurrence of nannofossils Reticulofenestra bisecta (Hay, Mohler and Wade) Roth. Two new species are described: Pentadinium rugosum Vasilyeva, n. sp. (dinocyst) and Corannulus tauricum Musatov, n. sp. (nannofossil). The bioevents and biozones established herein are significant for correlations of the Middle Eocene of the Crimean Peninsula and the south of the Russian Platform.

ИССЛЕДОВАНИЕ ПРИРОДЫ СЕЙСМИЧЕСКИХ СОБЫТИЙ В РАЙОНЕ ПХГ ПРИВОЛЖСКОГО ФЕДЕРАЛЬНОГО ОКРУГА

Seismicity during UGS operation had not yet been known in Russia. This work presents studies on the manifestation of seismicity in the area of three underground gas storages (UGSs) located in the south-eastern part of the East European Platform (European part of Russia). The tectonic structure of this region, geodynamic conditions and technological characteristics of «Vostochnoye», «Zapadnoye», «Uzhnoye» UGS are presented. An analysis of the situation with the manifestation of seismicity allows us to conclude that it is technogenic in nature, a feature not previously noted on Russian UGSs. There is a wide list of signs indicating the relationship between the mode of operation of UGSs and the nature of seismicity: prior to the start of UGS operation technogenic seismicity in this area was not known; there is a clear correlation between UGS operation and seismicity; the epicenters of seismic phenomena are located in the geodynamic influence zone of the UGS; in the region there are Earth crustal faults that experienced activation in late Cenozoic time and respond to strong earthquakes of neighboring tectonic areas, which consequently indicates their predisposition to reactivation; the change in pressure in the UGS reservoir is sufficient to induce seismicity. The phenomenon of increasing seismic activity during the gas extraction period is noted, which is explained by the effect of softening of the containing massif and its subsequent push-like deformation when the gas pressure in the reservoir is reduced. Despite the weak seismicity, which does not pose a threat to UGS facilities and adjacent territories, it is proposed to include seismic observations in the complex geodynamic monitoring at Russian UGS to establish patterns over a long period of time.

Discovery of Late Mississippian (late Serpukhovian)-Early Pennsylvanian (earliest Bashkirian?) foraminiferal assemblages from the Sanandaj-Sirjan Zone, Iran: Biostratigraphic and palaeoenvironmental implications.

This study reports the new discovery of relatively abundant foraminiferal faunas from the upper Serpukhovian-lowermost Bashkirian? of the Ghaleh Formation in the Shahreza region of the Sanandaj-Sirjan Zone, Iran. Four successive assemblages spanning the upper Serpukhovian-lowermost Bashkirian? are proposed: (1) Assemblage with Biseriella minima and Eostaffellina paraprotvae; (2) Assemblage with Bradyina cribrostomata; (3) Assemblage with Parastaffella utkaensa and Plectostaffella spp., (4) Assemblage with Plectostaffella ex gr. varvariensis. The newly discovered foraminiferal assemblages of the Sanandaj-Sirjan Zone have some species in common with assemblages of the Russian Platform, Donets Basin, Urals, and Western Europe. Ikensieformis aff. mirifica, and Eostaffella igoi, and a new species Ikensieformis persiaensis sp. nov. are described. The microfacies analysis of the Ghaleh Formation limestones suggests a moderate to high-energy shallow marine warm environment, more likely of the inner ramp.