Eastern Russian Platform Research Articles

Quartz Grain Microtextures in the Paleogene Sosnov Formation: Implications for Sediment Provenance in the Eastern Russian Platform

The purpose of the research. The chief task of the research is to examine the microtextures of quartz grains in the Paleogene Sosnov Formation, which is a sedimentary unit located in the Ulyanovsk-Syzran Volga Region of the Russian Platform. By examining the microtextures, which include mechanical, chemical and mechanical/chemical features, it becomes possible to find out the mechanisms by which grains were transported and subsequently modified. The relevance of the research. The relevance of this research lies in the fact that the analysis of quartz grain microtextures provides valuable insights into sediment provenance of sedimentary deposits is crucial for reconstructing past geological environments and unraveling depositional histories. Research methodology. Twenty quartz grains were collected from sands of the Paleogene Sosnovka Formation, exposed by the Eastern-Tashlinsky and the Kuchurovsky quarries to a depth of 5 and 7.5 m, respectively. The research methodology involved scanning electron microscopy (SEM) to investigate the microtextures of quartz grains. Results and conclusions. The study reveals 19 microtextures types, which were categorized into mechanical, chemical, and combined mechanical/chemical microtextures. An analysis of SEM indicated that chemical microtextures are present in the Paleogene Sosnov Formation, which made it possible to suggest that the sands passed through a low-energy phase during their transition. The data obtained enables us to reconstruct the diverse depositional paleoenvironments, including eolian, subaqueous, mixed subaqueous-eolian, and pedological settings.

Paleoclimatic conditions during the accumulation of the Upper Jurassic and Lower Cretaceous organic carbon-rich deposits of the Ulyanovsk-Saratov trough (eastern Russian platform)

Relevance of the work. Black shale horizons may reflect abrupt paleoclimate changes. In the northeast of the Ulyanovsk-Saratov Trough (UST), two black shale horizons widely occur, the Middle Volgian Promzino Formation and the Lower Aptian Ulyanovsk Formation. Despite years of research, the role of paleoclimate in their accumulation is still under discussion. The aim of the research was to assess the climate as a factor of the accumulation of the Middle Volgian and Lower Aptian organic carbon-rich deposits in the northeastern UST. Methods. To reconstruct paleoclimate and to evaluate its impact on the black shale deposition, a comprehensive isotope study of calcitic and aragonitic shells of several groups of benthic and pelagic organisms was performed. Besides, the lithological and geochemical features of organic carbon-rich and host deposits were studied using optical microscopy, XRD, and pyrolysis. Results. Isotope study allowed to construct benthic and pelagic palaeotemperature curves and to reconstruct paleoclimate in the UST during the formation of black shales. Based on these data and data on lithological and geochemical features of sediments, the depositional mechanisms of the Promzino and Ulyanovsk Formations were clarified. Conclusions. No causal link has been revealed between climate changes and the deposition of the Middle Volgian black shales. At the end of the Middle Volgian, a short-term cooling has been recorded, probably related to the volcanic activity of the northern Tethyan margin. The Lower Aptian black shales were formed during the hyperthermal. This hyperthermal controlled the accumulation of organic carbon-rich sediments by increasing the input of nutrients and/or providing conditions for its stratification and stagnation.

Paleogene sand injectites of the Uljanovsk-Syzran Volga region (eastern Russian platform)

Relevance of the work. The Paleogene quartz sandstones of the Sosnov Formation that occurred in the UlyanovskSyzran Volga region are known as a valuable source of glass raw materials being considered a scarce raw material of federal significance. But, predicting new deposits based on ideas of the coastal-marine origin of the Sosnov sands exhausted possibilities. The purpose of the work. The main aim of the work is to consider the Sosnov Formation is a complex of sand intrusions. The second one is to determine the possibility of improving the accuracy of forecasting new objects of sand raw materials. Methods. 35 sand samples from the Sosnov and the Bathonian Lukojanov Formation are analyzed using the inductively coupled plasma mass spectrometry and X-ray fluorescence analysis. The 3D-model of the Sosnov strata is constructed. Results. The Sosnov Formation is shown as a complex of sand injectites. The element geochemical study of the Sosnov and the Bathonian Lukojanov sands reveals a high possibility of their genetic similarity. The tectonic trigger of injectite formation is determined. The 3D-model of the Sosnov Formation constructed demonstrates the lateral and vertical variability of the sand deposit morphology. Conclusions. The geochemical study of the Sosnov and Lukojanov sands reveals the latter could be considered a possible source layer due to the genetic similarity of both strata. The tectonic trigger for the formation of sand intrusions was, most likely, the Late Paleocene activation of the Zhigulevskii fault. 3D-modeling of a particular sand deposit could improve the accuracy of predictive constructions.

Black shales contamination and depositional paleoenvironment during the Early Aptian OAE 1a in the Eastern Russian Platform

Black shales contamination and depositional paleoenvironment during the Early Aptian OAE 1a in the Eastern Russian Platform

Features of Seismic Impact Attenuation of the Russian Platform and Ural Earthquakes

The article analyzes the macroseismic impact of earthquakes that occurred in the late 20th and early 21st centuries on the Russian Platform and in the Urals. The relationships between seismic intensity I, magnitude M, and hypocentral distance r, according to the Blake–Shebalin equation, were established for five regions of the study area. For the first time, the coefficients of individual macroseismic field equations for the Ural near-surface and deeper sources were obtained (h ≤ 1 km: b = 1.5, v = 2.43, c = 1.01; h > 1 km: b = 1.5, v = 2.9, c = 2.13). The possibility of using the Blake–Shebalin equation with average coefficients (b = 1.5, v = 3.5, c = 3) was confirmed for earthquakes in southern Russian Platform. The low attenuation of the intensity of Baltic Sea earthquakes is established for the Eastern Baltics. The coefficient v = 2.48 in the obtained equation is similar to v = 2.7 recommended for this territory in the new Russian and Interstate Standard “Earthquakes: Macroseismic Intensity Scale” (2019). However, the level of seismic impact according to the established equation is higher than that predicted by this standard. The reduced attenuation coefficients for earthquakes in the eastern Russian Platform and induced events (h ≤ 1 km) in the eastern Baltic Shield have been obtained: v = 2.3 and v = 3.02, respectively. However, due to the lack of field data, these results need to be refined. New dependences are recommended for more accurate prediction of seismic impact from earthquakes in these regions.

Geochemical Indicators of “Camouflaged” Pyroclastic Material in the Upper Jurassic–Lower Cretaceous Deposits of the Eastern Russian Platform

Based on the results of studying the lithological–geochemical features of the Upper Jurassic–Lower Cretaceous mudrocks and black shales in the Eastern Russian Platform, the continuous distribution of pyroclastic material in the whole section is established. Possible sources of acid pyroclastics were active volcanoes of the Transcaucasian ensialic island arc. The explosions of the Sanandaj–Senjan ensimatic island arc (in the Late Jurassic) and the Arctic Large Igneous Province (in the Aptian) could have been the source of basaltic pyroclastics in the black shale horizons. The highest activity of the Transcaucasian and Elburs island arcs in northwest Tethys was apparently recorded during the Albian, which determined the maximum content of felsitic material in the Middle Albian bentonite-like mud rocks.

Early Cretaceous sea-level changes and major palaeoclimate events in the Northeastern Peri-Tethys

The Early Cretaceous quantitative sea-level curve constructed for the epeiric basin of the Eastern Russian Platform (Northeastern Peri-Tethys) is based on the results of facial analysis and quantitative paleo-depth assessment. The detailed evaluation of the Early Cretaceous sea-level cycles results in recognition of the sea-level and climate changes as controlling factors on depositional environments in the basin. Major climatic events are identified by the comparison between the global and regional sea level curves. “The cold snaps” coincide with simultaneous global and regional sea level lowstands, peak shallowing and the almost complete absence of strata. The Late Berriasian and Late Aptian “cold snaps” were identified in the Eastern Russian Platform. The Lower Aptian bituminous shales are interpreted as being a regional manifestation of the OAE 1a. The forcing mechanism behind this OAE is an abrupt rise in temperature.

Environmental perturbations during the Oceanic Anoxic Event 1a (Early Aptian) in the epeiric sea of the Eastern Russian Platform

Toxic environments are reconstructed during the OAE 1a in the epeiric sea of the Northeastern Peri-Tethys. Very high toxicity of sediments in conjunction with lack of oxygen could therefore result in conditions not suitable for benthic fauna dwelling. Black shales should be considered as one of the most important sources of the light carbon isotope in the atmosphere and oceans and the strongest emitters of methane. These data should be taken into account while estimating greenhouse effect in the Early Aptian. The environmental models constructed for the pre-OAE-1a, OAE-1a, and post-OAE-1a conditions may help to better understand modern climate changes using comprehensive analyses of oxic and euxinic conditions in the oceans and interpret the greenhouse processes from the geological past to the present time.

Mixed siliceous-carbonate sedimentation in a Late Cretaceous epeiric sea: New evidence from the eastern Russian Platform

Mixed siliceous-carbonate sedimentation in a Late Cretaceous epeiric sea: New evidence from the eastern Russian Platform

Euxinia as a dominant process during OAE1a (Early Aptian) on the Eastern Russian Platform and during OAE1b (Early Albian) in the Middle Caspian

A detailed study of the mineral composition and microstructure of the black shales associated with OAE1a (Eastern Russian Platform), OAE1b (Middle Caspian), and the host rocks has been carried out using X-ray diffraction, scanning electron microscopic, and microprobe analyses. The results provide important constraints for depositional environments in the sedimentary basins. Black shales with pyrite framboids imply euxinic (sulfidic) conditions with increased organic matter preservation. Disintegrating framboids suggest partial or complete dissolution of the organic matter inside the framboids due to increasing water oxygenation. OAE1a on the Eastern Russian Platform is heterogeneous as it includes thin interbeds of concretionary coccolith limestones within the interval of bituminous shales, and correlates with the Lower Aptian Rhagodiscus angustus nannofossil zone. The coccolith limestones indicate short intermittent episodes of interrupted stagnation, rapid oxygenation, and restoration of normal marine conditions. The presence of montmorillonite, albite, microcline, and diopside in the bituminous siltstones and in the host siltstones of OAE1a on the Eastern Russian Platform, as well as a high content of titanium in the black siltstones correlated with OAE1b in the Middle Caspian allow proposing significant input of pyroclastic material into the extant sea.

Mineralogical composition of the Lower and Upper Kazanian (Mid-Permian) rocks and facies distribution at the Petchischi region (Eastern Russian Platform)

The mineral composition proportions of carbonate rocks of Kazanian (Mid-Permian) age in the Petchischi region (eastern part of the Russian Platform) was identified by X-ray powder diffraction, ICP-MS and optical microscopy. The Lower Kazanian deposits are presented predominantly by bio-dolomicrites with changing terrigenous component and the lack of gypsum-bearing layers in the succession. Dolomicrites are prevalent in the Upper Kazanian succession, which is composed of alternation of gypsum-bearing dolomites, clayey dolomites and pure dolomites. The discovered bentonite-bearing component in marls and bentonite clays are proposed as evidence of volcanic activity in the Urals in the Kazanian stage. Two marine facies on the Eastern Russian Platform in the Kazanian: peritidal shallow flat and coastal sabkha agree well with the trends of δ18O and δ13C ratios.

Sea-level and climatic controls on Aptian depositional environments of the Eastern Russian Platform

On the basis of a high-resolution chronostratigraphic framework of the Eastern Russian Platform, a comparison between Late Barremian–Aptian global and regional sea-level trends was performed. The detailed evaluation of the long-term (3rd order) Aptian sea-level cycle results in the recognition of sea-level and climate as controlling factors on depositional environments in the basin. The rising part of the Aptian sea-level cycle lasted from the Deshayesites tenuicostatusis Zone to the Deshayesites deshayesi Zone, and transgression is responsible for the local development of anoxia on the Eastern Russian Platform. The Lower Aptian bituminous shales and sheeted calcite concretions associated with the Eastern Russian Platform are interpreted as being a regional manifestation of Oceanic Anoxic Event OAE 1a. The Late Aptian “cold snap” that occurred during the Early Cretaceous greenhouse world coincided with a simultaneous global and regional sea-level lowstand, peak shallowing of the basin, and the almost complete absence of sediments due to subaerial exposure in the studied region. The global distribution of the lowstand gives clear evidence for sea-level fluctuations, and intrinsic climate control on sequences in the study area.

Eustatic, tectonic, and climatic signatures in the Lower Cretaceous siliciclastic succession on the Eastern Russian Platform

A methodical approach to identifying major abiotic events in the siliciclastic succession accumulated in the shallow epicontinental basin on the Eastern Russian Platform during the Early Cretaceous is presented. On the basis of a reliable chronostratigraphic framework a comparison between global and regional sea level curves was undertaken. The intervals during which the global and regional sea level curve trends are similar correspond to a predominance of eustasy in the particular basin. Alternatively, tectonic activity dominates during intervals when there is no similarity between the trends of the global and regional sea level curves. Three intervals of noncoincidences of trends of these two curves matched with major tectonic events that took place within the Eastern Russian Platform in the Early Cretaceous: the Early Hauterivian tectonic uplift, subsequent Late Hauterivian subsidence and the Late Albian uplift. The main consequences of the tectonic activity were two large regional unconformities and hiati. The comparison of main global and regional sea level trends also reveals major climatic events. “The cold snaps” that occurred during the Early Cretaceous greenhouse world (Hu et al., 2012) coincided with simultaneous global and regional sea level lowstands, peak shallowing of the basin and the almost complete absence of sediments. “The cold snap” is identified in the Late Aptian sedimentary sequences on the Eastern Russian Platform.

In quest of Paleocene global-scale transgressions and regressions: constraints from a synthesis of regional trends

Chronostratigraphically-justified records of regional transgressions and regressions are important for understanding the nature of the Paleocene shoreline shifts on a global scale. Review of previously synthesized data from 7 tectonically “stable” regions, namely the eastern Russian Platform, Northwestern Europe, Northwestern Africa, Northeastern Africa, the Arabian Platform, the northern Gulf of Mexico, and Southern Australia, allows a comparison of transgressions and regressions interpreted in these regions. No common patterns are found in the early Danian and late Selandian, which reflects small or zero eustatic fluctuations that are overwhelmed locally on coastlines by regional tectonic motions and local changes in dynamic support of surface topography by mantle flow. Sea level was stabilized during these stages by a warm climate and a lack of planetary-scale tectonic changes. We have detected a middle–late Danian regression that occurred in 5 of 7 study regions, and can be explained by glacial advance at ∼62–63Ma or by concurrent subduction of the Izanagi–Pacific ridge beneath eastern Asia. An early–middle Selandian transgression also occurred in 5 regions, probably, as a result of a hyperthermal at ∼61Ma that coincided with emplacement of large igneous provinces in the oceanic domain. Both events are characterized by significant diachroneity, which can also be explained by the influence of regional tectonic subsidence or uplift. Results of the present study permit us to propose a tentative framework for a new Paleocene eustatic curve that is constrained globally using available records of transgressions and regressions.

A new species of Pelekysgnathus (Conodonts) from the Famennian of the east Russian Platform

A new conodont species, Pelekysgnathus aristovi sp. nov., from the Middle Famennian shallow-water carbonate deposits of the South Tatar Dome in the eastern Russian Platform is described.

No global-scale transgressive–regressive cycles in the Thanetian (Paleocene): Evidence from interregional correlation

A detailed examination of transgressions and regressions that occurred during the Thanetian (58.7–55.8 Ma) may provide an important constraint on the global palaeoenvironment. Seven tectonically “stable” regions (the eastern Russian Platform, Northwestern Europe, Northwestern Africa, Northeastern Africa, the Arabian Platform, the northern Gulf of Mexico, and Southern Australia), represent exceptional records of transgressive–regressive (T–R) cyclicity. Their chronostratigraphic frameworks are sufficiently well constrained to permit accurate correlation. Surprisingly, except for a generally regressive trend occurring in the late Thanetian, no common T–R cycles can be delineated, which indicates an absence of global-scale T–R cyclicity during the Thanetian. Furthermore, we find no clear correspondence between documented T–R patterns and previously reported eustatic changes. We suggest that a warm climate and an absence of major glaciations in the early-middle Thanetian, coupled with only slow eustatic change expected from tectonic processes, stabilized Thanetian eustatic sea level. Regional subsidence or uplift, possibly generated by mantle flow in the form of dynamic topography, governed transgressions and regressions locally and resulted in an inconsistency between T–R cycles in different parts of the globe. The late Thanetian regressive episode, which preceded the Paleocene–Eocene Thermal Maximum, may be linked to an advance of glaciation.

Geochemistry of isotopes (δ13C and δ18O) and depositional environment of the upper Kazanian carbonate sediments in the Volga-Vyatka interfluve

This work reports the results of lithological and isotopic study of carbonate rocks from the Pechishchi stratotype section (Kazan) and three adjacent sections of Kazanian rocks of the Volga-Vyatka region at the eastern Russian Platform. These sections were recovered by the Kremeshki, Popovtsevo, and Chimbulat quarries (near the town of Sovetsk, southeastern Kirov district). Lithological features and wide variations of δ13C (from −6.0 to 6.8‰) and δ18 O (from 22.9 to 33.4 ‰) indicate that the rocks were formed in a shallow-marine basin with rapidly varying conditions of sedimentation which characterize different facies (and/or paleoecological) zones: lagoonal, supralittoral, littoral, shoal. They also suggest processes of postsedimentary alteration (mainly, under supergene conditions). Numerous short-term hiatuses are also recorded.

A condensed succession at the Jurassic/Cretaceous transition in a shallowing basin on the eastern Russian Platform

The eastern periphery of the Russian Platform houses an exceptional record of the Jurassic/Cretaceous transition, which is represented by very thin sandstone beds. The presence of glaucony grains, phosphorite concretions and shark teeth indicates that the transitional sediments constitute a condensed succession, although the allochtonous origin of the glaucony grains in itself is not a reliable indicator. The combination with thin ammonite zones and a strongly diminished sedimentation rate, as low as ~0.05 cm/ka are, however, convincing evidence. The Jurassic/Cretaceous transitional deposits accumulated in a basin the depth of which decreased simultaneously with a global eustatic sea-level fall. This coincidence suggests that condensed successions may form in shallowing environments, which contradicts the sequence-stratigraphic concept. Considering the character of the sediments under study, it appears that both stratigraphic and taphonomic condensation patterns occur in this part of the eastern Russian Platform.

Frasnian conodonts from the eastern Russian Platform

The Frasnian conodonts of the eastern Russian Platform from the Timan in the north to the Orenburg Region in the south are characterized in detail both paleontologically and stratigraphically. This paper is a continuation of a previously published monograph (Ovnatanova and Kononova, 2001) on the Frasnian conodonts of the shallow-water strata of the central Russian Platform, where polygnathids prevail. The conodont assemblages from the shallow-water and basinal sections of the Volga-Ural province and Southern Timan are analyzed. Problems and difficulties associated with the correlation of the shallow-water and deep-water Frasnian sections of the eastern Russian Platform and their correlation with the existing zonal conodont scales are discussed. The correlation between the deep-water Mendym deposits and the shallow-water Rechitza and Voronezh strata of the Volga-Ural province with the Vetlasyan and Sirachoi deposits of the Southern Timan is substantiated. The stratotype of the Semiluki Regional Stage of the Central Devonian Field contains equivalents of the lowermost beds of the Domanik Formation (unit 1), based entirely on polygnathids. Phylogenetic reconstructions for Palmatolepis and Polygnathus are suggested based on the ontogenetic series for some species of these two genera and the presence of transitional forms between some of the species. Based on these phylogenetic reconstructions, conodont zonal scales for the shallow-water and deep-water sections of the Frasnian Stage of the Russian Platform are proposed and their correlation with the existing conodont zonal scales is also adduced. Some aspects of biofacies control are considered based on the distribution of conodonts in the sections studied. In Systematic Paleontology, 91 conodont species of the genera Ancyrodella, Mesotaxis, Palmatolepis, and Polygnathus are described, including the new species Palmatolepis menneri, P. kaledai, P. acutangularis, and Polygnathus reitlingerae.

98/01286 Major types, origin, and prospecting of uranium ore mineralizations in eastern Russian Platform: Khalezov, A. B. Rudy Met., 1996, (2), 48–54. (in Russian)

98/01286 Major types, origin, and prospecting of uranium ore mineralizations in eastern Russian Platform: Khalezov, A. B. Rudy Met., 1996, (2), 48–54. (in Russian)