Статьи журнала - Вестник геонаук
Все статьи: 1821
Статья научная
A new Tournaisian (Early Carboniferous) conodont Siphonodella puchkovi sp. nov. is described from the shallow-water clayey-carbonate deposits of the Pechora-Kozhva Uplift (Pechora Plate). Morphologically Siphonodella puchkovi is similar to its ancestral species Siphonodella quasinuda Gagiev, Kononova et Pazuhin but differs from it by longer outer rostral ridge, platform outline, and rounded posterior tip of platform. The new species occurs in the L . crenulata Zone ( carinata local zone) of the middle Tournaisian, and is known from the Timan-Pechora and Donets basins. Together with Siphonodella carinata and Hindeodus cristulus the new species is characteristic of this zone in the shallow-water facies.
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Aktas quartz in Central Kazakhstan is important raw for the production of hi-tech products
Статья научная
This study presents the investigation of the Aktas quartz deposit in the central part of Kazakhstan as a potential source of high-purity quartz (HPQ) for use as raw materials for special applications in high-technical industries especially solar energy industry. Geochemical studies revealed that the Aktas quartz deposit can be classified as pure quartz one due to its high silica content 99.21- 99.29 %. Also it is characterized by low contents of Al2O3, Fe2O3, CaO, MgO, Na2O3, K2O and P2O5. Therefore, the quartz of this deposit without preliminary treatment matches well the requirements of the Aluminum and Ferrosilicon alloy industries. The beneficiation processes that applied on the studied quartz samples of Aktas to remove the excess and undesirable high contents of mineral inclusions (hematite, pyrite and magnetite) and impurities (Fe2O3, TiO2, Al2O3, CaO... etc) are related to froth flotation in three stages. These stages were carried out at a fixed pH condition (5.5-6) but with changing the time of grinding (20, 40, 60 min, respectively). The beneficiation of Aktas quartz with froth flotation in the 1st stage (20 min time of grinding) displayed a marked increase of the SiO2 content and decrease of the Al2O3, Fe2O3 and CaO contents to a noticeable percent, while the 2nd and 3rd stages of flotation had a negative effect on the quartz and this is reflected by the decrease of SiO2 content (98.71 % in the 2nd stage and 98.83% in the 3rd stage of flotation) and increase of Fe2O3 content (0.58 % in the 2nd stage and 0.79% in the 3rd stage of flotation), therefore the 1st stage of flotation is recommended (grinding time 20 min and the pH 5.5-6), because it gives better results. The beneficiation processes with froth flotation at a fixed condition (pH 5,5-6 and 20 min time of grinding) allowed the use of the quartz of Aktas for the production of silicon carbide.
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Borogypsum: mineral composition, processing technology
Статья научная
We have chosen borogypsum for our study, which contains gypsum and silicon dioxide used in various industries. Present methods of borogypsum processing were considered. A new flotation reagent was proposed to separate the silicon concentrate from boric acid production waste. With the help of methods of mathematical planning, a multifactor experiment was carried out to reveal the optimal mode of flotation. We chose the following factors: temperature, pH, concentration of the main flotation reagent, agitation time, and also the time of flotation. The results of an experimental study of the raw material and obtained samples were presented with the help of modern physicochemical methods (spectrophotometry, IR spectroscopy, scanning electron microscopy, X-ray phase analysis), which allowed studying the chemical and mineral compositions and the structure of the samples. The new flotation concentration technology from boric acid wastes was developed.
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Boron in late precambrian igneous formations of the Northwestern Pay-Khoy
Статья научная
The first results of the determination of boron content in igneous rocks of the Morozov (RF3 mr ) and Sokolninsk (RF3-V sk ) Formation and the Morozov (bRF3 mr ) subvolcanic bodies of the northwestern Pay-Khoy are reported. Elevated boron concentrations may indicate the presence of sedimentary material in the magma source, where boron can be introduced during the dehydration of oceanic sediments that enter the subduction zone along with the slab material. Transverse geochemical zoning in the island arc system of the Morozov paleoarc is expressed by increasing concentration of boron in magmatites from the frontal zone (boron content 12-18 ppm) to the rear (boron content 19-45 ppm), which is due to the ingress of a larger volume of sedimentary material by the time of the formation of melts in the rear part of the arc. The boron concentration in the basalts of the Sokolninsk Formation varies from 17 to 22 ppm, which indicates the entry of a smaller volume of sedimentary material into the magma generation area during the formation of the Sokolninsk paleoarc.
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Статья научная
Carbon isotopy of individual aromatic compounds of petroleum for their geochemistry understanding
Статья научная
The article analyzes published and original data related to the carbon isotopic composition of individual aromatic compounds of fossil organic matter and oil. It has been shown that there is reliable evidence of the intramolecular isotopic heterogeneity of a number of molecules. For example the isotopically depleted carbon of the methyl group of alkylnaphthalenes and the terminal methyl of n-alkanes. The 13C inheritance from the biochemical precursor during the aromatization is also well documented in the example of diterpenes in the series abietic acid - dehydroabietane - simonellite - retene, as well as in the other terpene and steroid series. At the same time, there is evidence of carbon isotopic fractionation during the formation of several aromatic compounds from a single precursor. The increasing aromatization of the prebuild polycyclic structure does not change the 13C value of the molecule, and the formation of aromatic compounds with different numbers of aromatic rings in competing reactions leads to isotope differentiation in accordance with the thermodynamically determined distribution of carbon isotopes. If the suggestion is correct, it is the key to the understanding of specific petroleum aromatic hydrocarbons formation mechanism. It is possible that a comparison of 13C values for pairs of compounds formed during the transformation of one precursor will also provide information on the temperature conditions for the occurrence of the corresponding reactions.
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Cathodoluminescence of conodont elements
Статья научная
Conodont elements are used as a geochemical archive of seawater. Some compositional features of conodont elements reflect conodont ecology and trophic structure of Palaeozoic pelagic ecosystems. However, the screening of conodont elements prior to geochemical and/or isotopic studies is a real problem. This study evaluates SEM cathodoluminescence (SEM-CL), which is very sensitive to the REE and Mn content of apatite, for the detection of traces of secondary transformation in the composition of conodont bioapatite. The SEM-CL of conodont elements is similar to that of unaltered shark teeth (blue-violet), but differs significantly from that of fossil vertebrate teeth (orange-red). Thermal alteration has little effect on the SEM-CL. Elements with a CAI of 1-1.5 show a redder and more intense CL than elements with a CAI of 5. In the case of corrosion of the conodont element surface in carbonate host rocks, the CL of the outer parts of the conodont element become reddish due to invasion of the carbonate material. Conodont elements from the clay host rock show deep purple SEM-CL. Thus, SEM-CL allows detection of the results of secondary processes in conodont mineralised tissues, including enrichment by REE and/or Mn, corrosion and contamination by carbonate material. This method can be used to screen significantly altered samples prior to chemical and isotopic analyses.
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Comparative histology of conodonts and early vertebrates
Статья научная
The study of the histology of the Late Devonian and Early Carboniferous conodont elements allows characterizing the main types of hard tissues, composing a conodont element crown: lamellar, paralamellar, interlamellar, and albid. Significant differences between texture and composition of the conodont hard tissues and those of Vertebrata are detected. Some similarities observed in the structures of the conodont and vertebrate mineralized tissues may be caused by similar process of biomineralization, not by synplesiomorphy.
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Complex geophysical investigations of the West Timan fault
Статья научная
In this paper we discuss results of complex geophysical works within the southern and middle segments of the West Timan fault. In the study area, based on the nature of potential fields (magnetic, gravitational), various areas of the West Timan fault were identified: the southern part (Beloborsk block), the central part (Nivshera block), and the northern part (Sindor block). These areas were studied by profile magnetometry on foot and express radon survey. The detailed magnetic survey revealed that the West Timan fault was clearly visible in the gradient sections of the magnetic field, with some degree of conventionality it can be identified within the regional maximum, and it is impossible to trace it in the zone of the regional minimum. Based on the interpretation of seismic data, the location of the West Timan fault has been clarified. The nature of the seismic record does not always allow identifying the exact location of the fold planes, only the difference in the record in individual blocks is clearly noted. The border area sometimes captures 5 km. The express emanation survey showed that the West Timan thrust, in general, was characterized by increased values of radon volumetric activity, where they are further traced to the territory of Timan, while areas of different intensity are distinguished.
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Conodonts and ostracodes from the givetian-frasnian shallow-water deposits of the Southern Timan
Статья научная
Conodont and ostracode distribution in the Timan (Middle - Upper Devonian, Upper Givetian - Lower Frasnian), Ust’-Yarega (Upper Devonian, Lower Frasnian) and Yba (Middle? - Upper Devonian, Upper Givetian? - Lower Frasnian) formations of Southern Timan was analyzed. The regional and interregional correlation of the established associations was conducted. The significant changes in conodont and ostracode associations are observed almost at the base of the Ust’-Yarega Formation, and they are associated with a gradual increase in the depth of the paleobasin. The conodonts of Ancyrodella rugosa and Mesotaxis asymmetricus appearing at this level characterize the Ancyrodella rugosa conodont Zone. The ostracodes of the Ust’-Yarega Formation are represented by the assemblage of the Cavellina chvorostanensis - Entomozoe (R.) scabrosa Zone. The significant changes in the conodont associations of the Yba Formation reflect an important sequence of appearance of the index-species: Mesotaxis falsiovalis , Ancyrodella rotundiloba soluta , Ancyrodella rotundiloba rotundiloba . The Ancyrodella soluta conodont Zone provide a reliable correlation of the sections of the Timan-North Urals Region and are essential for resolving the issue of the lower boundary of the Frasnian stage of the Upper Devonian in the East European Platform.
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Crystallization features of calcium sulfate in the process of “artificial aging”
Краткое сообщение
Gypsum binders are widely used in construction, mining and the oil and gas industry. The use of these binders is conditioned by stability of their technical characteristics, which is achieved by using a technological operation “artificial aging”. The features of artificial aging are: 1) hydration of calcium sulphate hemihydrate in liquid phase deficiency; 2) the resulting dihydrate gypsum crystallizes in a limited volume of micropores of the original binder. From the standpoint of the quataronic concept, the features of the crystallization of gypsum dihydrate in the micropores of the original gypsum binder are considered. The effect of artificial aging conditions and the degree of supersaturation on the growth mechanism and the morphology of gypsum dihydrate crystals was determined. The use of artificial “aging” results in healing of defects in the structure of the original binder, decreasing water demand and increasing strength.
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Devonian and early carboniferous coals and the evolution of wetlands
Статья научная
The rise of forests in the Mid and Late Devonian has attracted much attention as potential drivers of the Earth System. In this context it is important to understand what groups contribute to the first wetlands found at the Devonian palaeoequator. A time series of Devonian coals shows that the palaeoequatorial Mid and Late Devonian humic (vitrinite rich) coals are dominated by the lycopod microspore Cymbosporites and megaspore Verrucisporites that can be confidently associated as the spores from Protolepidodendropsis . This plant has successfully colonised and probably created the wetland coal environment by the ability to shallow root and hence anchor the trees above the anaerobic layer. The progymnosperm Archaeopteris is abundant from its spores in Devonian palaeoequatorial sediments but plays no role in these coal forming wetlands. More rigorous age dating shows that there is some evidence for a Tournaisian coal gap.
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Статья научная
The representative sections outcropping shallow-water and deep-water Devonian/Carboniferous successions in the East of Pechora Plate (Kamenka River section and Vangyr River section) are considered in respect of facies, conodont, and ostracode changes. In the Kamenka River section the D/C boundary beds are composed of bioclastic limestones interbedded with dark-gray clays (lower part of the Edzhid Fm.). The deposits contain abundant and diverse benthic ostracodes of Pseudoleperditia tuberculifera - Coryellina alba - Cribroconcha primaris ostracode Zone, and diverse conodont associations of praesulcata and sulcata zones. The negative shifts in d13Corg in conodont organic matter accompanied by weak positive shift in d13Ccarb in bulk carbonates suggest eutrophic conditions in the lagoon environment and disbalancing of the trophic web at the terminal Famennian. D/C boundary beds in the Vangyr River section are represented by calciturbidites, pelagic carbonates, and shales (Izyayu Fm.). Transgressive phase of Hangenberg Event is marked by the black shale layers. The Upper Famennian conodont associations are dominated by Palmatolepis gracilis group; the ostracodes compose diverse associations of Turingian and slope ecotypes. The D/C boundary is marked by appearance of conodonts Siphonodella sulcata in associations with ostracodes Armilla uralica .
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Elastic-anisotropic properties of the upper mantle high-pressure xenoliths, the Spitsbergen island
Статья научная
The paper presents the results of the study of elastic anisotropic properties of high-pressure xenolith (Spitsbergen) represented by olivinites and orthopyroxenes. According to the analysis, the rocks were erupted from the upper mantle. The highly informative method of acoustopolariscopy was used. The average calculated values of density (r C = 3.28 g/cm 3), compression ( VP C = 8.2 km/s) and shear ( VS C = 4.92 km/s) wave velocities were obtained. The experimental density values, on average, are 7.1 % lower than the calculated ones, the velocities of compression waves are 36 % lower and the shear wave velocities are 34 % lower. These values can be used when interpreting the results of deep seismic data.
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Electroacoustic properties of various types of quartz in the finely dispersed state
Статья научная
An electroacoustic echo method for studying the high-frequency (HF) electrical and elastic properties of piezoelectric materials in a finely dispersed state is described. The characteristics and relaxation time of electroacoustic echo for natural and artificial quartz powders are determined. Natural one is represented by the following types: smoky quartz, citrine, amethyst, recrystallized, granular and columnar. It is shown that natural quartz (especially citrine), has a higher electromechanical coupling coefficient than artificial quartz. The amplitudes of HF electric field are determined, at which the saturation mode of the echo signals is observed.
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Статья научная
The new lithology and facies model of the Lower Devonian Lochkovian deposits according to complex studying of well sections on the northeast of the Timan-Pechora Province is offered. The ostracodes fauna, in view of their multiplicity and euryfaciality has appeared the most useful for the decision. Ostracodes complexes for the first time allowed not only to trace laterial change of the Lochkovian deposits but also to incorporate them in the geophysical correlation datum framework.
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Статья обзорная
It is pointed out that corundum is the only natural modification with corundum Al and O packing motif, which determines the physical and chemical features of noble corundum. Based on the authors' ideas about the genesis of noble corundum with the application of original analytical data, which clarify the consolidated literature data, corundums of the magmatic, metamorphic and detrital series are defined. A scheme of the location of the main deposits of noble corundums of the world is given. It is stated that all properties of noble corundums are determined by their primary indigenous origin. The general condition of corundum formation is protocrystallization from melts in deep magmatic centers under the condition of subsequent rapid solidification of the main mass of the melt. The presented research methods allow determining characteristics and a wide range of application of corundums. Precambrian corundum deposits are of the prevailing genetic type.
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Статья научная
Based on the results of the core analysis of boundary Lower to Upper Devonian (D1l-D3tm) interval by X-ray fluorescence analysis supplemented with CO2 determination and loss on ignition, X-ray diffraction analysis of clay fraction of the rocks and clays, electron microscopy and EDS, analysis of stable isotopes of carbonate carbon and oxygen, etc., we revealed lithological and mineralogical-geochemical features, which testified to the ancient influence of infiltration water systems to the rocks during the ascent of previously submerged strata into the aeration zone. In the sections studied, we showed a definite vertical geochemical zonation, expressed in changing zones from top to bottom: a) zone of marine slightly altered limestones; b) zone of hydrolysis and infiltration in argillaceous dolomites with signs of paleokarst; c) zone of secondary dolomites; d) zone of low-altered limestones. The established sequence is characteristic for the processes of regressive infiltration epigenesis and assumes the existence of a subaerial unconformity between a and b zones.
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