East European Platform Research Articles

Isotopic Sm-Nd signatures of Precambrian Banded Iron Formation from the Fennoscandian shield, East-European Platform, and Bundelkhand craton, India

In this communication, we report geochemical and Sm-Nd isotope data of Banded Iron Formation (BIF) from Kola-Karelia (Fennoscandian shield), East-European Platform and Bundelkhand craton, N-E India. The BIFs from Kola-Karelia (Algoma type), and Bundelkhand Craton (Algoma type), north-central India, and East-European Platform (Superior type) characterized by alternate domains of quartz-rich and iron-rich layers. Except for magnetite and hematite, orthopyroxene, amphibole, and garnet are the other dominant minerals present the BIF’s. The shale-normalized REE spectra of iron-rich layers of Bundelkhand, Kola-Karelia and East European BIFs are similar. The εNd[t] for silica-rich layers is higher compared to the iron-rich layers for all studied samples. The higher εNd[t] values (around +5.0) for silica-rich layers from Kola-Karelia, Bundelkhand BIF and East European Platform suggest a juvenile source for silica. The lower εNd[t] values (−5 to +2) for iron-rich layers from the same samples implies continental source for the iron. The present study suggests that the sedimentation mechanisms of silica and iron for Algoma as well as Superior types BIFs are similar despite spatial diversity.

Structure and evolution of Belomorian-Severodvinsk shear zone in the Late Proterozoic and Phanerozoic, East-European Platform

Tectonics, morphological features and development stages of Belomorian-Severodvinsk shear zone (north-western part) found in the East European platform are considered. We traced the shear zone (length ≈1000 km) from NW to SE from the Baltic shield to the Russian plate sedimentary cover. It inherited Paleoproterozoic structures of Belomorian-Lapland mobile belt and Riphean grabens of the White Sea rift system. Belomorian-Severodvinsk zone was represented in the modern structure by a system of neotectonic grabens limited by normal and normal–strike sleep faults and segmented by the transform fault zones. We came to conclusion that the shear zone experienced multiple repeated activation in different dynamic conditions in the Riphean–Phanerozoic. Cyclic alternation of riftogenic trans-tension and compression or transpression conditions in the sequence stages of its development was noted. We defined three cycles of transtensive-transpressive transformations of Belomorian-Severodvinsk shear zone in the Riphean and the Early Vendian. At least four times shear zone suffered changes of deformation mode and directions of shear displacement in the Phanerozoic. The postglacial neotectonic deformations in the Belomorian-Severodvinsk shear zone revealed under the Kola block horizontal movement to the S–E and subsequent counterclockwise rotation.

Petrogenesis of Synplutonic High-Mg Porphyritic Dikes from Mafic–Granitoid Plutons of the Voronezh Crystalline Massif, East European Platform

Abstract—The paper reports data on the high-Mg porphyrite dikes (PD) in the ~2.09 Ma mafic to felsic plutons of the Elan Complex (EC). Thin (a few cm thick) synplutonic dikes are characterized by the sharp even contacts without visible chill zones, unlike thicker (up to 119 m thick) dikes with gradual transitions. The dikes are fresh, porphyritic (bronzite, Al-enstatite, and labradorite phenocrysts) with fine-grained mainly quartz–feldspar (+biotite, sulfides, accessories, ±hypersthene) groundmass. Based on chemistry, the PD are intermediate rocks (SiO2 = 58.9–60.3 wt %) ascribed to the calc-alkaline series with high magnesian (Mg# ~0.7) whole-rock composition and felsic (68.9–70.2 wt %) groundmass (Mg# ~0.5). The porphyrites have fractionated REE distribution pattern without sharp Eu anomalies. Bronzite phenocrysts of variable size show patchy zoning and contain unevenly distributed inclusions of olivine (Mg# ~0.85), clinopyroxene (Mg# ~0.88), phlogopite (Mg# up to 0.94), labradorite, chromite, graphite, and sulfide. Al-enstatite phenocrysts are almost devoid of trace elements and mineral inclusions. Geochemical features, as well as the presence of diffusion zones, reaction rims, and resorbed facets in the orthopyroxene and plagioclase phenocrysts serve as evidence for disequilibrium recrystallization and/or partial dissolution of the crystals and intratelluric nature of dike phenocrysts, the core of which was inherited from derivatives/cumulates of the EC. Mineral thermometry showed that: (1) the initial temperatures of parental magma are 1200–1400°С, (2) the crystallization temperatures of the EC are 1080–1155°С, and (3) the emplacement temperatures of the PD are 910–1070°С. Petrological model suggests that the high-temperature boninite-like EC magmas were generated from the metasomatized upper mantle. The parental melt was contaminated by continental crust rocks. The existence of an transitional evolved magma chamber is inferred in the crust. At the final stage of its evolution, the PD melt intruded yet hot EC plutons.

Long-term shoreline shifts on continental blocks during the Bajocian: an updated interpretation based on synthetic stratigraphical and palaeogeographical developments on regional scales

Abstract Available reconstructions of Jurassic global sea level changes differ and are in need of an update. New stratigraphical charts and palaeogeographical developments for a number of large continental blocks or their portions of these (e.g., Germany, India, northeast Africa, northwest Australia, the Russian Platform and western Siberia) reveal regional long-term shoreline shifts (i.e., transgressions and regressions) during the Bajocian Stage (168.3–170.3 Ma). A comparison of these allows to document only a single coherent feature, namely the earliest Bajocian transgression, in the majority of the continental blocks considered. Undoubtedly, this event was triggered by a eustatic rise. However, long-term shoreline shifts were either weak to absent or differed between the blocks during almost the entire Bajocian, thus providing evidence of the apparent stability of global sea level and the importance of regional tectonic activity as a control mechanism on particular transgressions and regressions. Interestingly, it appears that the earliest Bajocian eustatic rise was a constituent of a long-term eustatic pattern; the nature of this event has yet to be fully understood. Generally, the findings presented here are in better agreement with Anthony Hallam’s view of Jurassic eustasy and question some other global sea level reconstructions.

Assessment of the Seismic Impact of Industrial Explosions in the Central Part of the East European Platform

The attenuation coefficients of longitudinal and shear waves propagating in the Earth’s upper crust below the central region of the East European Platform have been determined using seismic observations along a profile from the Novogurovskii limestone quarry to the Mikhnevo small-aperture seismic array. Assuming that dissipative properties of the Earth’s crust are invariable, we drew a contour map characterizing the propagation of seismic energy generated by open pit mine blasting in the central part of the East European Platform; the map reflects both historical and recent earthquakes as well. The distribution of seismic impacts of industrial explosions is compared with the distribution of zones of tectonic dislocations revealed by lineament analysis. The map also contains estimates of the intensity of open pit blasting in 2013–2017.

Evolutionary significance of the retiolitine Gothograptus (Graptolithina) with four new species from the Silurian of the East European Platform (Baltica), Poland and Lithuania.

Gothograptid retiolitines were distinctive in being one of the very few graptolite groups to thrive through the late Wenlock extinction event that killed off most graptoloid species, and their distinctive construction may have been a factor in this success amid environmental adversity. New and rich material from two localities in Poland and five localities in Lithuania contains Gothograptus nassa, Gothograptus obtectus and four new species. The detailed morphology and reconstruction of the tubarium shows its specific features, different from other lundgreni Biozone retiolitines. The tubarium is narrow, elongated, finite, massive and compact. The thecal orifices are hidden by simple hoods or by extraordinary reticulated veils, which may cover the ventral walls. The colonies of Gothograptus species from the lundgreni Biozone are short, usually having eight pairs of thecae, whereas species from the post-lundgreni interval may reach more than 20 pairs of thecae. A common feature of Gothograptus species is the presence of singular genicular structures tightly covering thecal orifices. Reticulated hoods and veils are characteristic of species from the lundgreni Biozone. The most common such structures are nassa hoods, located on the proximal thecae in some species from the lundgreni Biozone, and on every theca of post-lundgreni species. Only Gothograptus domeyki n. sp. has no genicular processes on most thecae. Within a total of four species from the lundgreni Biozone and three species from the nassa and praedeubeli Biozones, we describe here the new species Gothograptus domeyki and Gothograptus velo from the lundgreni Biozone, Gothograptus diminutus from the parvus/nassa Biozone, and Gothograptus auriculatus from the dubius/nassa and praedeubeli biozones; G. auriculatus n. sp. is the youngest form of the genus Gothograptus. Variation within the genus Gothograptus during the post-lundgreni interval period is shown for the first time.

The main geodynamic border and seismic visualization of plumes under the East European Platform

According to the Taylor approximation method of the three-dimensional P-velocity mantle model under Eurasia, a seismic imaging of the manifold plumes and super-deep fluid processes of the East European Platform was carried out. As the source data, the time of the first wave of R wave entry according to the ISC bulletins from 1964 to 2006 was used. The fluid domain is defined as the region of distribution of low-speed inhomogeneities from the lower, middle mantle to the upper and spreading laterally in the upper end of its central part. The central, low-speed part of the fluid domain is defined as a plume. On the territory of the East European platform, the North-Azov, Volyn-Orsha, Moscow, Timan, Belomorsky, Varanger and Schelfteo plumes are highlighted. In the area of spreading the data of mantle domains there are 19 super-deep mantle fluids. By the nature of the behaviour of the gradient of velocity with depth, the main geodynamic boundary (the boundary between the upper and middle mantle) is constructed, which within the East European platform ranges from 525 to 700 km. According to the depths of the main geodynamic boundary, the East European platform is divided into Fennoscandia (575 km), Sarmatia (divided into two parts with depths of 575 km and 600—625 km) and Volga-Uralia (625 km). The main geodynamic boundary of the Barents Sea plate is divided into East and West (525—550 km). For the given main geodynamic boundary, the reduction of the gradient of speed (sharpness) from north to south from 0.734 s–1 in the mantle under the archipelago Medvezhy to the average is mostly £ 0.2 s–1 in the mantle North of 55° northern latitude.

The deep structure of the Dobrogea and Fore-Dobrogea trough as an indication of the development of the Trans-European suture zone

The tectonic structure of Dobrogea and Fore-Dobrogea trough are considered on the basis of geological and geophysical data. Dobrogea and Fore-Dobrogea trough are the key areas for understanding of Central Europe geodynamics, because they are located within the southeastern part of the Trans-European Suture Zone (TESZ), which is available here for direct field research. The current position of these units in the foreland of the Carpathians and on the north-eastern coast of the Black Sea makes them a link that connects the Pannonian-Carpathian region and Crimean-Black Sea region. The deep structure of the study area is described by the velocity models of wide-angle reflection and refraction (WARR) profiles VRANCEA-2001, DOBRE-4 and PANCAKE. Dobrogea is a system of northeastern vergence overthrusts, separated by a series of large faults. These faults, most important of which is Pecenega-Camena Fault, are part of the southern branch of the TESZ. The width of the Dobrogea thrust zone is about 60 km and close to the width of the thrust zone along PANCAKE profile. The modern fold and thrust structure of Dobrogea was formed on the place of the paleopaleozoic suture in Cimmerian tectonic stage (Upper Jurassic—Lower Cretaceous) and activated in the Early-Alpine stage (Upper Cretaceous—Paleogene), being later than the Jurassic, and earlier than the Alpine thrusting in the Pannonian-Carpathian region. Taking into consideration the geological and geophysical similarity of Rava-Ruska and North-Dobrogea elements of the East European platform, as well as similarity of the Inner zone of the Lviv Paleozoic trough and the Fore-Dobrogea trough, it can be suggested that within the study area, the northeast boundary of the TESZ passes close to the surface beneath the Fore-Dobrogea trough, while the southwest boundary coinside with the Peceneaga-Camena Fault and may even cross it at the boundary of the upper and middle crust. According to the data of the WARR profiles DOBRE-4 and PANCAKE, the TESZ is considered not to be vertical zone, but gently dipping system of overthrusts separated the East European platform from the Western European and Moesian platforms.

Electrical conductivity of the crust and mantle of the East European platform in the western part of Ukraine from 2D inversion

2D inversion of the magnetotelluric and magnetovariational data along 40 profiles made it possible to create overview model of electric resistivity for the territory between eastern longitudes 28° and 36° and by the northern latitudes 47.8° and 52°. Analysis of sections of resistances in the depth interval from 5 to 105 km indicate the absence of objects of low resistance (less than 100 Ohm × m — OLR), the dimensions of which would allow them to be called a layer. The geometrical parameters of the OLR indicate their locality. Along the border of the East European platform are geoelectric objects of low and high (more than 4000 Ohm × m — HO) resistances, at low depths of 20 km low-resistance objects prevail. Comparison of anomalous geoelectrical objects (OLR and HO) with fault tectonics, metallogeny, oil and gas content and modern activation shows that most of the OLR are confined to fault nodes, in which nodes and areas are often concentrated of minerals having an electronic type of conductivity (graphite, polymetallic ore and noble metals). The areas promising for oil and gas content, identified on the maps of various authors, are partially consistent with the Yavoriv, Lokachi, Ternopil and Chernivtsi zones of modern activation, and in this case are accompanied by conducting objects. It is interesting to note the consistency of geological and geophysical conclusions about the prospects of the North-West oil and gas province with the presence of the OLR. Depth and power of conducting objects allows to assume the presence of a gene-tic connection of various minerals not only with sedimentary metamorphosed rocks, but also with the presence of deep fluids. It seems that the results obtained can contribute to the development of ideas about the deep structure of the studied territory and its connection with both existing deposits of various minerals and during the spillage of new ones.

Tectonic structure of the zone of conjugation of the Eastern European piatform and the Scythian plate (territory of the Rostov region)

The tectonic structure in the junction zone of the East European and Scythian platforms of Rostov region has been considered. Different ages and ranks of Precambrian and Phanerozoic tectonic structures, their correlation within the studied area and tectonic zoning scheme are presented. The structure and composition of rock complexes, formation conditions and their tectonic development stages are characterized. The East European platform within the described territory is represented by two disconnected fragments of the Russian Plate. The northern fragment is the south-eastern part of the Voronezh anteclise, located to the north of the Donetsk-Astrakhan tectonic suture. The southern fragment corresponds to the eastern dipping of the Pre-Paleozoic rocks of the Ukrainian shield, forming the buried Rostov ledge. The Scythian (Epihercynian) platform located to the south of the Donetsk-Astrakhan tectonic suture, is represented by a folded Paleozoic (in some places pre-middle-Jurassic) base and a platform cover of Mesozoic-Cenozoic rocks. The part of the Scythian platform is the exposed Donbass area, where Paleozoic rocks of the base of the platform protrude to the surface and form the Donetsk ledge. The northern part of the Scythian plate, which extends over the buried folds system of Donbass, is allocated from the south by Manych over-fault deflections and called «Karpinsky shaft». The system of the Manych deflections and the territory located to the south compile the Ciscaucasian part of the Scythian plate.

Striking Variation in the Provenance of the Lower and Upper Cretaceous Turbidites in the Central Pontides (Northern Turkey) Related to the Opening of the Black Sea

AbstractThe Lower and Upper Cretaceous turbidites cover large areas in the central Pontides (north‐central Turkey). The Lower Cretaceous turbidites are over 2 km thick and are exposed in an area of 400 × 90 km. The Upper Cretaceous (Campanian‐Maastrichtian) forearc turbidites are up to 1,200 m thick and crop out in NW‐SE trending elongate basins about 40 km wide, extending along the central and eastern Pontides. We present new detrital zircon U–Pb ages, petrography, and paleocurrent measurements from the Campanian‐Maastrichtian turbidites and compare them to those from the Lower Cretaceous turbidites. The Campanian‐Maastrichtian sandstones are dominated by carbonate and magmatic lithic grains. The paleocurrents indicate paleoflow directions parallel to the axis of the basin. The sandstones are dominated by Late Cretaceous zircons indicating derivation mainly from the coeval magmatic arc. In contrast, the Lower Cretaceous sandstones are dominated by quartz and feldspar, and paleocurrents indicate southward transport. The detrital zircons in the Lower Cretaceous sandstones are mainly Archean and Paleoproterozoic, indicating that in the Early Cretaceous, the source of turbidites was from the Archean‐Paleoproterozoic Ukrainian Shield to the north. After the opening of the Black Sea in the Late Cretaceous, the connection between the Pontides and the East European Platform was severed and the Campanian‐Maastrichtian turbidites were sourced principally from the magmatic arc in the Pontides. Our results indicate that the Campanian‐Maastrichtian turbidites represent the first turbiditic sequence deposited after the opening of the Black Sea.

Seismotectonic Setting of the Earthquake of August 7, 2016 and its Aftershocks

On August 7, 2016, an earthquake with magnitude 4.8 occurred in the vicinity of the city of Mariupol close to the southern boundary of the East European Platform (EEP). The earthquake was accompanied by aftershocks with magnitudes ranging from 2.2 to 3.9 that lasted for five days. This region experiences external influence from the neotectonically active Alpine zone, which is expressed in intraplate deformations, horizontal and vertical movements of the Earth’s surface, and seismicity. The sources of the earthquake and its aftershocks are located within the block bounded by the neotectonically active Maloyanisol, Kalmius, and Primorsky faults. In the axial part of the block, a seismogenic structure is traced by the submeridional Kalchik lineament zone identified by the combined analysis of geological and geophysical data and visual interpretation of the satellite image. This neotectonically active zone accommodates the epicenters of the main event and most of the aftershocks.

Late Vendian kotlinian crisis on the East European Platform: lithogeochemical indicators of depositional environment

Sharp changes in the biodiversity of fossil organisms in the Upper Vendian of the East European Platform are considered as the manifestation of global crisis immediately prior to the “Cambrian Explosion.” However, they could be caused by local environmental perturbations. Variations of some lithogeochemical indicators of depositional environment (indicators of paleoclimate, exhalation activity, redox settings, and paleobioproductivity) were analyzed in order to establish the possible influence of sedimentary systems on evolutionary processes in the Late Vendian and at the boundary with the Cambrian. The applied algorithm of lithogeochemical studies revealed no significant perturbations in physical properties of the environment on a scale of sedimentary basins. The obtained data suggest that local factors did not affect the evolution of Ediacaran biota on the East European Platform and confirm the global nature of transitions between the Redkinian, Belomorian, and Kotlinian biotas.

Flora of the Kazanian–Urzhumian boundary in the middle Permian of the Russian Platform

Rich fossil plant localities in the upper Guadalupian and the lowermost Lopingian of the Russian Platform are confined to several discrete “levels” or “horizons” divided by intervals that are almost devoid of plant remains. One such “horizon” is located at the boundary between the Upper Kazanian and the Urzhumian of the regional stratigraphic scale. Numerous localities of this level can be grouped into two geographical clusters, the northern one being confined to the Kama River Basin, and the southern one to the Orenburg Region and Southern Bashkortostan. Regarding the southern localities, three floras that are seemingly successive in time can be distinguished. Against a common background of articulates (Paracalamites and Equisetites), the lowermost flora is characterized by the dominance of leaves of Rufloria (Cordaitanthales) with very rare conifers. Conifers (Quadrocladus, Sashinia, Dvinostrobus) and leaves of Phylladoderma (Peltaspermales) are the most abundant elements of the middle assemblage, whereas Rufloria leaves are very seldom found together with the peltasperm Ginkgophyllum and the conifer-like Steirophyllum. The uppermost flora is dominated by Odontopteridium and Ustyugia, two closely related genera of peltasperms, whereas cordaitaleans are totally absent. Comparison with the northern localities, which can be linked to the type sections of the Upper Kazanian and the Urzhumian, enables the dating of these assemblages in terms of the regional stratigraphic scale. All three floras prove to be confined to the uppermost Kazanian, and only the youngest one could also occur in the lowermost Urzhumian. As the stratigraphic ranges of all observed plant taxa exceed the total stratigraphic interval under study, the sequence of the floras seems to be caused by ecological (most likely climatic) factors rather than the actual evolution of plants. In particular, the observed gradual elimination of cordaitaleans confirms the general view on the extinction of this group on the Russian Platform. The southwestern boundary of the occurrence of cordaitaleans on the Russian Platform stretched from the southwest to the northeast, approximately parallel to the palaeolatitudes reconstructed on the basis of palaeomagnetic data. During the Guadalupian it moved to the northeast, which is to the north considering the position of the North Pole of that time. Cordaitaleans were the main peat-forming plants in the Late Palaeozoic of northern Pangea (in the Kuznetsk, Tunguska and Pechora Basins). So their retreat to the north was most likely a consequence and a reflection of the warming and drying of the climate.

Precise U-Pb age constrains on the Ediacaran biota in Podolia, East European Platform, Ukraine

The Neoproterozoic Era was characterized by rapidly changing paleogeography, global climate changes and especially by the rise and fall of the Ediacaran macro-biota. The correlation between disparate Ediacaran fossil-bearing localities and the tentative reconstruction of their paleoenvironmental and paleogeographic contexts are usually complicated by the lack of precise and accurate age data. For this reason, Neoproterozoic sedimentary sections associating Ediacaran biota fossils and fresh volcanic material are especially valuable for radioisotopic dating. Our research in the Podolya Basin, southwestern Ukraine, revealed the presence of four Neoproterozoic volcanic ash deposits (potassium-bentonite layers) within Ediacaran fossil-bearing siliciclastic rocks of the Mohyliv-Podilskyi Group. We used zircon U-Pb LA-ICPMS and CA-ID-TIMS methods to date two of those layers. The results indicate that a diverse assemblage of body and trace Ediacaran fossils occurred as early as 556.78 ± 0.18 million years (Ma) ago. By combining morphological evidence and new age determinations, we suggest a closer paleobiogeographical relationship between the Ukrainian Ediacaran assemblage and the Avalon paleocontinent than previously estimated.

Biogeostatistics confirm: Even a low total number of red wood ant nests provide new information on tectonics in the East Carpathian Orogen (Romania)

Recent statistical analyses revealed that the spatial distribution of nests of red wood ants (RWA; Formica rufa-group) and actively degassing fault zone are strongly correlated. We now applied the modified Hough Transform (mHT) and Iterative Mode Detection (IMD) to RWA nest positions in four study areas of the Eastern Carpathian Orogen. The aim of this analysis was (1) to evaluate relationships between spatial distribution of RWA nests and complex tectonic stress regimes in the Eastern Carpathian Orogen, (2) to test if this procedure is also applicable even when only a low total number of RWA nests is available, and (3) to further verify the validity of this statistic approach. By applying a double-blind study, we minimized bias by researchers’ preconceptions. Since irregular shapes of the study areas were found to strongly influence the findings of distribution patterns, all subsequent analyses were carried out for circular areas. Statistical results substantiated our hypothesis that RWA nest distributions clearly show very pronounced directions even in complex tectonic environments such as the Eastern Carpathian Orogen. Dominant NW-SE directions (scattering between 120° and 150°) are corresponding to the 1st order regional stress field in the East Carpathians. Additionally, our analyses revealed the 2nd order stress field in NE-SW orientation. Furthermore, directions of re-activated shear systems, e.g. from Late Miocene and Pliocene that had been modified by overprinting due to changes of the main stress field, could be identified. For the Moldavian and East European Platform, which are characterized by thick sediment cover, our analyses could significantly contribute to otherwise concealed tectonics. Furthermore, the mode of some faults identified in previous tectonic studies could be complemented and specified and assigned to the corresponding tectonic regime. Our study thus confirms the validity of our statistic approach even when the total number of RWA nests is low.

Response of cephalopod communities on abrupt environmental changes during the early Aptian OAE1a in the Middle Russian Sea

Significant influence of anoxic events on faunal turnovers in marine communities is well-established. However, many studies are focused on the impact of anoxic conditions on benthic organisms, while coeval changes in pelagic cephalopod assemblages remain relatively poorly understood. In the present paper we discuss the trends in cephalopod assemblages coinciding with the onset of the early Aptian black shale deposition in European Russia coeval with OAE1a. In few sections of the Saratov Volga area (central part of the Russian Platform), representing both offshore and more proximal nearshore lithofacies of the epicontinental Middle Russian Sea, we have recognized simultaneous changes in ammonite and belemnite successions. Belemnites, represented by the late members of the family Oxyteuthididae, are common in the interval directly preceding anoxic event, but totally disappear with the onset of the black shale deposition. For the Deshayesites ammonites shell size reduction across the mudstone – black shale boundary (maximum shell diameter of adults reduces from ∼20 cm to 7–8 cm) can be observed. Some other ammonites become numerous (Sinzovia) within the black shale interval or show a first occurrence in it (Koeneniceras and Volgoceratoides). In our opinion diminishing of Deshayesites shell size during the early Aptian OAE could be caused by coupling of palaeoenvironmental factors such as progressive warming and regional input of brackish water. Preliminary results of carbon isotope studies of aragonite deriving from the ammonite nacreous layer are also provided.

Mineral and geochemical composition of the Onega Ice Lake sediments

An analysis of the mineral-geochemical composition and structure of the Holocene–Pleistocene bottom sediments was performed on Lake Polevskoye, a small lake in the northern Lake Onega area in Russian Karelia, which is considered representative to describe the Late Weichselian Onega Ice Lake sediments. The analysis was accomplished using modern analytical methods, including scanning electron microscopy and ICP-MS, which allowed us to interpret their genesis in a new light. It is assumed that the distribution of rare earth elements (REE) in the bottom sediments of the recent Lake Onega and in the sediments of Onega Ice Lake will improve our understanding of the history of sedimentogenesis. It is apparent in the distribution of REE, their composition and data on the geochemical and mineral composition of the Holocene bottom sediments of Lake Onega and Lake Polevskoye (varved clays) that in their composition of terrigenous matter the material introduced from the north-western part of the catchment area is mainly composed of Archaean and Early Proterozoic crystalline complexes. However, the values of several indicator ratios of elements in the lower part of the of varved clays with shungite interlayers indicate the presence of mixing of clastic material from two sources of different geochemical origin: the north-western part of the catchment area (source of shungite rocks) and the south-eastern part of the catchment area (Phanerozoic sedimentary rocks of the Russian Platform).

Thermal history of Lower Palaeozoic rocks from the East European Platform margin of Poland based on K-Ar age dating and illite-smectite palaeothermometry

Large-scale shale gas prospecting in the Polish part of the East European Platform did not discover large reserves of this resources. The article presents new research indicating that one of the reasons for the lack of shale gas relates to the thermal history of the Lower Palaeozoic rocks. Illite-smectite palaeothermometry was used to reconstruct the history of the platform and determine the maximum temperatures to which these rocks were subjected. The age of illitisation was also constrained using the K-Ar method. This method allowed precise dating of the maximum age of thermal transformations due to the deposition of numerous pyroclastic horizons (K-bentonite) throughout the entire geological profile from the Cambrian to the Silurian. Isotopic dating was made on over 53 samples of Lower Palaeozoic bentonites and low-grade metamorphic clays. These results were supplemented by analysis of the degree of thermal (smectite to illite) transformation in the profiles of 37 deep boreholes. 11 zones could be distinguished with different tectonic histories within the Polish part of the East European Platform edge. Maximum heating occurred in this region at about 320–340 Ma, corresponding to the Early Carboniferous or the turn of the Early and Late Carboniferous, phase A of the Variscan orogeny, known as the Sudetian phase. In the southern part of study area, the maximum of thermodiagenesis is slightly younger – 270–290 Ma, which responds to the Early Permian, the Asturian phase, the last phase of the Variscan orogeny. This means that the generation of hydrocarbons occurred before significant Mesozoic exhumation of the Polish part of the East European Platform, which led to the escape of a considerable amount of the gas generated. The study also presents the results of an interlaboratory comparison of illite age dating using the K-Ar and Ar-Ar methods. The comparison was conducted to find out what realistic error should be considered when interpreting geological K-Ar dating results.

Structure and Evolution of the Belomorian–Severodvinsk Shear Zone in the Late Proterozoic and Phanerozoic, East European Platform

Structure and Evolution of the Belomorian–Severodvinsk Shear Zone in the Late Proterozoic and Phanerozoic, East European Platform