pdf № 322, October

DOI: 10.19110/geov.2021.10.1

The article considers isolated carbonate platforms known in the Sub-Polar Urals (basin of the Bolshaya Nadota River; boreholes of the Yunyakha and Levaya Grubeyu areas) and the NW Pay-Khoy (basin of the Lymbad’yakha River and coast of the Barents Sea). The three stages of formation of the platforms (Frasnian, Famennian-Tournaisian, and Visean-Serpukhovian) are distinguished, and the sedimentological models of these platforms are developed. Subsidence curves based on the back-striping demonstrate some differences in the evolution of the studied isolated carbonate platforms. Similarities and differences in the history and structure of the platforms are observed. Formation of the intra-shelf depressions (the Kozhim Depression in the Sub-Polar Urals, and the Korotaikha Depression in the Pay-Khoy) in the Frasnian — Early Famennian caused appearance of isolated carbonate platforms. The depressions probably were formed by the regional tectonics. The following development of the carbonate platforms was controlled by eustatic fluctuations. The isolated platforms differ by stratigraphic spans (Late Frasnian — Serpukhovian for the Polar Urals Platform and Famennian-Tournaisian for the Pay-Khoy Platform), relief, facies, and size. The isolated depressions differ in size as well: the Kozhim Depression is larger than the Korotaikha Depression. Additionally, it is supposed that the Polar Urals platform was of warm-water type, but the Pay-Khoy platfrom was of cool-water type.

Keywords: Pay-Khoy, Sub-Polar Urals, Upper Devonian, Lower Carboniferous, isolated carbonate platform, models of sedimentation.

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DOI: 10.19110/geov.2021.10.2

The article presents the results of CHIME (chemical Th–U-total Pb isochron method) dating of monazite from metamorphic rocks of Precambrian complexes located in the north part of the West Spitsbergen Island. It is shown that for rocks of Atomfjella Series and Mossel Series, monazite ages are coeval within error (Atomfjella Series: 381 ± 18 Ma, Mossel Series: 377 ± 23 Ma). These age estimates show that metamorphism of the crystalline basement possibly took place during the Late Caledonian orogeny.

Keywords: monazite, CHIME, metamorphism, Caledonian orogeny, Ny Frisland, Spitsbergen.

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DOI: 10.19110/geov.2021.10.3

The obtained evidence of hot heterogeneous accretion of the Earth leads to a fundamentally new solution of the problem of the genesis of Early Precambrian crystal complexes. According to this approach, a powerful impact heat release during accretion resulted in the formation of a layered global magmatic ocean. Its upper acidic layer arose from low-pressure residual melts of the bottom parts of the still shallow early ocean, fractionated under the influence of an increase in the load pressure of the forming upper layers. The solidification of the uppermost parts of the acidic layer led to the formation of the most ancient tonalite-trondyemite complexes. Gneiss-crystalshale complexes were formed from its deeper parts by lowering the crystallized near-surface areas together with sediments accumulated on them and lifting the underlying magmas of often more mafic composition in their place. Leaching of the near-surface parts of the solidified rocks under the influence of acidic emanations of the magmatic ocean caused the predominance of quartzites and high-alumina gneisses among the oldest pararocks. Due to the solidification of the magmatic ocean from top to bottom, the isotopic age of gneiss decreases on average with depth. The surfacing of residual melts of its various layers led to the evolution of magmatism of ancient platforms from acidic to alkaline-ultrabasic and kimberlite. The separation of ore-bearing emanations of the magmatic ocean caused the formation of numerous often unique deposits.

Keywords: Early Precambrian, magmatic ocean, crystalline crust.

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DOI: 10.19110/geov.2021.10.4

The treatment with N-methylpyrrolidone of sedimentary rocks of the Ayuvinskoye deposit allowed obtaining ash-free concentrates with different yields, depending on the Corg content in the rock. The structure of the resulting concentrates was studied by elemental analysis, thermogravimetry, and pyrolysis, followed by analysis of the products by gas chromatography-mass spectrometry. The TGA curves indicated similar structural features of the organic matter of the rocks and the concentrates obtained from them. The composition of the thermolysis products of the concentrate indicated the preferential extraction of aliphatic structures, represented by n-alkyl chains, relative to aromatic fragments, which was associated with the specific structure of the initial organic matter of solid fossil fuels.

Keywords: oil shale of the Ayuvinskoe deposit, ash-free concentrate, pyrolysis, gas chromatography-mass spectrometry, thermogravimetry.

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DOI: 10.19110/geov.2021.10.5

Siliceous-carbonate rocks are widespread on the territory of the Republic of Dagestan, in which the total content of zeolites and opal-cristobalite-tridymite phase (OCT) exceeds 45 %, and the content of calcite is above 30 %. The rocks, composing a productive stratum (at least, most of it), lithologically correspond to opoka-like and highly siliceous limestones, zeolite-containing (10–15 %) and zeolite (40 % or more), weakly quartz and weakly clayey. However, they are distinguished from pure limestones by a low value of actual calcite part — often less than 50 %. Therefore, in this case, the section of the productive strata is defined as «folded by siliceous-carbonate zeolite-containing rocks.» Such rocks, in accordance with the results of laboratory and technological study, are considered as raw materials for the production of building materials. Zeolite-containing rocks are suitable for use as an additive in Portland cement, which will save cement clinker in the production process and improve the quality of cement.

Prospecting works for zeolites and zeolite-containing rocks in the Levashinskaya (Levashinsky district) and Rubaschayskaya (Tabasaran and Kaitagsky districts) areas of Mountainous Dagestan were carried out by the non-metallic party of JSC Sevkavgeologiya in 2007–2009. The resources of siliceous zeolite-containing rocks are in the P1 category — 49.308 million tons, in the P2 category — 69.470 million tons. The predicted resources, their laboratory and technological properties (physicochemical, chemical, technological) indicate the possibility of creating a solid mineral resource base and construction of large complexes for the extraction and processing of zeolites and siliceous rocks in Levashinsky (Levoberezhny and Pravoberezhny areas) and Tabasaran (Dyubek area) regions of the Republic of Dagestan.

Keywords: Siliceous rocks, carbonate rocks, opal-cristobalite-tridymite, zeolites, green marls, reservoir, cement, Levashinskaya area.

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