pdf № 329, May

DOI: 10.19110/geov.2022.5.1

The paper presents the novel isotope data on the age of sandstones of the gold-bearing Alkesvozhskaya sequence at the base of the Paleozoic section in the Subpolar Urals. The analysis of U/Pb dating of detrital zircons confirmed that the sandstones had been formed no earlier than in the Late Cambrian-Early Ordovician. The predominant part of dating is in a narrow Late Riphean-Late Cambrian age interval, and zircons are represented by unrounded or weakly rounded crystals. The composition of the sandstones of the Alkesvozhskaya sequence are dominated by the destruction products of the underlying rocks of igneous complexes at various stages of the formation of timanides-protouralides.

Keywords: zircon, Late Cambrian, Early Ordovician, Alkesvozhskaya strata, Sablegorskaya formation, Subpolar Urals.

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DOI: 10.19110/geov.2022.5.2

The paper describes lithological and geochemical features of the Lower Triassic sandstones from the far north of Timan-Pechora oil and gas-bearing province. These sandstones chemically coincide to typical graywackes.

We discuss how sedimentation environments and diagenesis control the local heterogeneity of cementation, variability of void space and the potential oil content.

Tectonic conditions are one of the provenance factors, the figurative points of the composition of sandstones on the diagrams fall into the field of the passive continental margin. The position of sandstone points on the diagrams and low values of the hydrolyzate module indicate the formation of deposits in an arid climate, which does not contradict to geological data.

Keywords: Triassic deposits, sedimentation, facies, environments, sandstones, graywackes, oil and gas reservoirs, geochemical module.

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DOI: 10.19110/geov.2022.5.3

The peatlands of the Arctic territories are repositories of radioactive contaminations. The physicochemical properties, specific activity and features of vertical migration of ⁹⁰Sr in the peat profile of the Murmansk region have been studied. A correlation matrix was compiled according to the studied indicators. The factor that determines the localization of ⁹⁰Sr in peat has been established. The sources of isotope for the region were determined.

The reaction of the peat medium is acidic (4.2 ≤ pH_water ≤ 4.9; 3.6 ≤ pH_salt ≤ 4.1). The ash content of peat is medium and high (5.2 % ≤ А_sh ≤ 28 %). The share of organic matter in the peat profile is more than 70 %. The upper part of the profile is saline (soluble salts > 0.3 %). The share of carbonates in the peat profile is insignificant (0.42—0.83 %).

⁹⁰Sr activity (0.55—7.7 Bq/kg) was recorded in each peat sample. The activity of the technogenic radionuclide is below the established permissible norm and within the range typical for all Russian soils. The ⁹⁰Sr isotope is localized in the upper layers of the profile and at a depth of more than 16 cm. The localization of ⁹⁰Sr in peat layers is due to the content of water-soluble salts (r = 0.85). The main sources of the isotope for the Murmansk region are past global fallout from nuclear tests, the Chernobyl accident and current local fallout from nuclear fuel facilities.

Keywords: peat bog, physical and chemical properties, strontium-90 (⁹⁰Sr), vertical migration, Murmansk region.

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DOI: 10.19110/geov.2022.5.4

The results of vertical variability comparative studies of the chemical snow layers composition, chronologically linked to the stratigraphically significant snowfall periods, have been presented. The features of the impurity elements concentration on geochemical barriers in the snow mass have been shown. The formation mechanism in the seasonal snow cover has been discussed.

Keywords: snow cover, geochemical barriers, deep frost, crystal formation, impurity elements.

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