35 research outputs found

    Water–rock interaction within the oligotrophic peat bog (part of the Vasyugan Swamp, Western Siberia)

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    Geochemical conditions of the formation of various minerals were studied within the oligotrophic pine-shrub and sphagnum peat bog. It was shown that at least two complex barriers function within the peat deposit. These barriers correspond to the changes in the advective and diffusion transfer of substances and promote the immobilization of Fe and a number of other chemical elements. The upper complex geochemical (redox, sulfide and sorption) barrier occurs approximately at the depths of 0.40 to 1.25 m. The lower complex geochemical (alkaline and sorption) and mechanical barriers are located at the bottom part of the peat deposit (the depth of 2.25–2.50 m)

    Structural-chemical features and morphology of glauconites in sedimentary iron ore of Bakchar prospect (Western Siberia)

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    The research embraces the investigation results of glauconites in Bakchar iron ore occurrences to evaluate the potential diversified commercial application of this mineral. The following lab methods were used to analyze the morphology, chemical composition and structure of glauconites: granulometric analysis, optical microscopy, electron microscopy, X-ray fluorescence analysis, atomic arc-emission analysis and infrared spectroscopy. Glauconite was classified according to morphology and grain color and chemical composition and some specific characteristics were also determined (relative content of absorbed water, random distribution of smectite flakes within the grain structures). The research results showed that pistacho-green glauconite grains are less subjected to alteration than greenish-yellow grains due to the content of potassium, iron, absorbed water and organic impurities

    The Formation of Authigenic Carbonates at a Methane Seep Site in the Northern Part of the Laptev Sea

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    Authigenic carbonates from cold seeps are unique archives for studying environmental conditions, including biogeochemical processes associated with methane-rich fluid migration through the sediment column. The aim of this research was to study major oxide, mineralogical, and stable isotopic compositions of cold-seep authigenic carbonates collected in the northern part of the Laptev Sea. These carbonates are represented by Mg-calcite with an Mg content of 2% to 8%. The ?13C values range from ?27.5‰ to ?28.2‰ Vienna Peedee belemnite (VPDB) and indicate that carbonates formed due to anaerobic oxidation of methane, most likely thermogenic in origin. The authigenic pyrite in Mg-calcite is evidence of sulfate reduction during carbonate precipitation. The ?18O values of carbonates vary from 3.5‰ to 3.8‰ VPDB. The calculated ?18Ofluid values show that pore water temperature for precipitated Mg-calcite was comparable to bottom seawater temperature. The presence of authigenic carbonate in the upper horizons of sediments suggests that the sulfate–methane transition zone is shallowly below the sediment–water interface

    Minerals of Rare Earth Elements in High-Phosphorus Ooidal Ironstones of the Western Siberia and Turgai Depression

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    The aim of this research was to study the rare earth (REE) minerals in ooidal ironstone deposits of the West Siberian basin and the Turgai depression. Authigenic minerals (monazite and cerite) were described, and their main mineral form was identified as light rare earth element phosphate (LREE-phosphate) in this study. LREE-phosphate is included in ferruginous ooids, peloids, and oncoids and forms a consistent mineral association with Fe-hydroxides (goethite and its hydrated amorphous derivatives) and Fe-rich layered silicates (Fe-illite-smectite, chamosite, berthierine). The constancy of the mineral association in two deposits of different ages indicates a general mechanism behind the formation of these minerals. LREE-phosphates (authigenic monazite) are characterized by microscopic sizes (up to 24 ?m), diverse morphology (mainly spherical or xenomorphic), and occupy spaces between the micro-cortex in ferruginous spheroids. This mineral can be found in other deposits of ooidal ironstone. According to its mineralogical and chemical characteristics, LREE-phosphate mainly belongs to the authigenic (nodular or “gray”) monazite. However, the incomplete (not 100%) correspondence of Kikuchi bands with the reference monazite does not allow its reliable identification. Based on its small size, chemical leaching or bacterial interaction is recommended to extract REE from ooidal ironstone while predicting the associated removal of phosphorus from iron ore due to its dominant phosphate mineral form. Ooidal ironstone should be considered a complex deposit and an unconventional natural type of REE ores as an example of the largest Bakchar and Lisakovsk deposits

    Authigenic and Detrital Minerals in Peat Environment of Vasyugan Swamp, Western Siberia†

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    Studies of mineral-forming processes in modern peat bogs can shed light on metal concentrations and their cycling in similar environments, especially in geological paleoanalogs. In terms of the mineralogical and geochemical evolution of peat bog environments, the Vasyugan Swamp in Western Siberia is a unique scientific object. Twelve peat samples were collected from the Vasyugan Swamp up to the depth of 275 cm at 25 cm intervals. The studied peat deposit section is represented by oligotrophic (0-100 cm), mesotrophic (100-175 cm), and eutrophic (175-275 cm) peat, and this is underlain by basal sediments (from 275 cm). About 30 minerals were detected using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The observed minerals are divided into detrital, clay, and authigenic phases. The detrital minerals found included quartz, feldspar, ilmenite, rutile, magnetite, zircon, and monazite. When passing from basal to oligotrophic bog sediments, the clay minerals changed from illite-smectite to kaolinite. Authigenic minerals are represented by carbonates (calcite and dolomite), iron (hydro-)oxides, galena, sphalerite, pyrite, chalcopyrite, Zn-Pb-S mineral, barite, baritocelestine, celestine, tetrahedrite, cassiterite, REE phosphate, etc. The regular distribution of mineral inclusions in peat is associated with the (bio)geochemical evolution of the environment. The formation of authigenic Zn, Pb and Sb sulfides is mainly confined to anaerobic conditions that exist in the eutrophic peat and basal sediments. The maximum amount of pyrite is associated with the interval of 225-250 cm, which is the zone of transition from basal sediments to eutrophic peat. The formation of carbonate minerals and the decreasing concentration of clay in the association with local sulfide formation (galena, sphalerite, chalcopyrite, stibnite) begins above this interval. The peak of specific carbonation appears in the 125-150 cm interval of the mesotrophic peat, which is characterized by pH 4.9-4.5 of pore water. Kaolinite is the dominant clay mineral in the oligotrophic peat. Gypsum, galena, chalcopyrite, sphalerite, and relicts of carbonate are noted in association with kaolinite. Changes in oxygen concentrations are reflected in newly formed mineral associations in corresponding intervals of the peat. This can be explained by the activity of microbiological processes such as the anaerobic oxidation of methane (AOM) and bacterial sulfate reduction (BSR), expressed in specific carbonatization (100-225 cm) and sulfidization (175-250 cm), respectively

    Ooidal ironstones in the Meso-Cenozoic sequences in western Siberia: assessment of formation processes and relationship with regional and global earth processes

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    This study investigates the process of formation of ooidal ironstones in the Upper Cretaceous-Paleogene succession in western Siberia. The formation of such carbonate-based ironstones is a continuing problem in sedimentary geology, and in this study, we use a variety of data and proxies assembled from core samples to develop a model to explain how the ooidal ironstones formed. Research on pyrite framboids and geochemical redox proxies reveals three intervals of oceanic hypoxia during the deposition of marine ooidal ironstones in the Late Cretaceous to the Early Paleogene Bakchar ironstone deposit in western Siberia; the absence of pyrite indicates oxic conditions for the remaining sequence. While goethite formed in oxic depositional condition, chamosite, pyrite and siderite represented hypoxic seawater. Euhedral pyrite crystals form through a series of transition originating from massive aggregate followed by normal and polygonal framboid. Sediments associated with goethite-chamosite ironstones, encompassing hypoxic intervals exhibit positive cerium, negative europium, and negative yttrium anomalies. Mercury anomalies, associated with the initial stages of hypoxia, correlate with global volcanic events. Redox sensitive proxies and ore mineral assemblages of deposits reflect hydrothermal activation. Rifting and global volcanism possibly induced hydrothermal convection in the sedimentary cover of western Siberia, and released iron-rich fluid and methane in coastal and shallow marine environments. This investigation, therefore, reveals a potential geological connection between Large Igneous Provinces (LIPs), marine hypoxia, rifting and the formation of ooidal ironstones in ancient West Siberian Sea

    Ooidal ironstones in the Meso-Cenozoic sequences in western Siberia: assessment of formation processes and relationship with regional and global earth processes

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    This study investigates the process of formation of ooidal ironstones in the Upper Cretaceous-Paleogene succession in western Siberia. The formation of such carbonate-based ironstones is a continuing problem in sedimentary geology, and in this study, we use a variety of data and proxies assembled from core samples to develop a model to explain how the ooidal ironstones formed. Research on pyrite framboids and geochemical redox proxies reveals three intervals of oceanic hypoxia during the deposition of marine ooidal ironstones in the Late Cretaceous to the Early Paleogene Bakchar ironstone deposit in western Siberia; the absence of pyrite indicates oxic conditions for the remaining sequence. While goethite formed in oxic depositional condition, chamosite, pyrite and siderite represented hypoxic seawater. Euhedral pyrite crystals form through a series of transition originating from massive aggregate followed by normal and polygonal framboid. Sediments associated with goethite-chamosite ironstones, encompassing hypoxic intervals exhibit positive cerium, negative europium, and negative yttrium anomalies. Mercury anomalies, associated with the initial stages of hypoxia, correlate with global volcanic events. Redox sensitive proxies and ore mineral assemblages of deposits reflect hydrothermal activation. Rifting and global volcanism possibly induced hydrothermal convection in the sedimentary cover of western Siberia, and released iron-rich fluid and methane in coastal and shallow marine environments. This investigation, therefore, reveals a potential geological connection between Large Igneous Provinces (LIPs), marine hypoxia, rifting and the formation of ooidal ironstones in ancient West Siberian Sea

    Changes of chemical composition of waters in east part of the Vasyugan mire (Western Siberia)

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    Relevance. Studies of changes in chemical composition of mire waters is the important part of research of environment and climate changes at ecological monitoring at oil and gas exploration, limitation of anthropogenous influences on water objects and efficiency of estimation of contaminated lands reclamation. The aim of the research is to reveal the long-term and intraannual changes of chemical composition of mire waters in east part of the Vasyugan mire. Methods: landscape-geochemical and statistical methods, methods of definition of chemical composition of mire waters, thermodynamic calculations. Results and conclusions. The authors have analyzed the time changes in chemical composition of waters of east part of the Vasyugan mire (the Western Siberia, the Ob river basin, the Tomsk region) within the limits of three intramire ecosystems (mesotrophic border of ryam; ryam (Russian) - oligotrophic pine-dwarf-shrub-sphagnum raised bog; hollow-ridge complex - mire type which combines ridges and hollows). It is shown that for 2003-2017 there were no statistically significant changes of chemical composition of mire waters in active horizon of a peat deposit. Observable fluctuations of hydrochemical parameters are caused by variability of atmospheric humidifying which remains statistically constant in an annual section of the period of 1965-2016. Hydrochemical regime of mesotrophic border differs in the highest variability of total dissolved solids of mire waters and dependence on atmospheric precipitation value, and hydrochemical regime of ryam is characterized by the least influence of atmospheric precipitation. The common features of hydrochemical regime of all of three ecosystems is the certain reduction of mineralization during spring flood and increase in N-, P-, Si-substances and microelements in winter low water

    Resource efficient search strategies of oil deposits in the pre.jurassic base of Western Siberia

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    As a result of researches within the framework of the Federal Target Program «Researches and developments on priority directions of scientifictechnological complex of Russia for 2007-2013» the search strategy of oilperspective objects in preJurassic complex in central part of Western Siberia was developed and proposed, the bases of research technology were established. The authors have carried out marketing researches to analyze the competitive environment, to define consumers and to estimate the efficiency, to develop the implementation reference. Analysis of external documentation and technicaleconomic analysis of the research results was used as the research techniques. By the example of three fields in KhantyMansiysk Autonomous District it was shown that the new strategy provides the increase of resources growth to 60 %, capital costs decrease by 16 % and geological prospecting risk reduce. The strategy can be applied for regional studies, prospecting work and revaluation of oil field areas resources, subsoil licensing. The potential customers are the companies developing the Lower Jurassic fields and deposits. Resource efficiency of the strategy consists in ability to buildup resource base on the lands which already possess the functions of oil fields with the developed infrastructure, reducing costs on field construction and excluding costs on external communication

    Settings of current sedimentation on the underwater slope of Buor-Khaya bay (Laptev sea)

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    Nowadays, the Arctic shelf is of increasing interest due to its large reserves of hydrocarbons and other mineral resources. Meanwhile, current knowledge about the processes occurring in the Arctic is still extremely inadequate. There is still not enough data on natural processes within permafrost, which raises many problems and discussions around regional issues. Therefore, new scientific information can further promote the study of the Arctic nature. This study was aimed to identify the specific features of sedimentation and organic matter transformation in the coastal zone of the Arctic seas based on long-term observations. The objects of the study are suspended matter and bottom sediments, including organic carbon content (Corg) and its isotope composition as markers of lithodynamics of the modern depositional environment. Bottom sediments samples were investigated for grain-size composition, organic carbon content and isotopic composition. Furthermore, spatio-temporal variability of the suspended matter distribution in the water column was estimated. Conclusions: for the ice-free period, there are two typical stable turbidity maxima with a suspended matter content ranging from 6,5 to 594 mg/l. Towards the continental slope, the replacement of sandy-aleuritic sediments with clays of continental slope, avandelt bottom, and thermoabrasive-accumulative terrace is accompanied by an increase in organic carbon values from 0,4 to 5,4 % with winter values ranging from 0,6 to 9,3 %. Isotopic composition of organic carbon in the bottom sediments varied from -27,9 to -22,7
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