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Vol. 25 (2022 year), No. 1, DOI: 10.21443/1560-9278-2022-25-1
Zakharova A. A., Voytekhovsky Yu. L., Kompanchenko A. A., Neradovsky Yu. N.
Methodology for determination of petrographic structures using the MIU-5M device
The authors develop a statistical method for determining the structures of rocks. A mathematically rigorous definition of the petrographic structure through the probabilities of binary intergranular contacts is proposed. The petrographic structure is defined as an invariant aspect of rock organization algebraically expressed by the canonical diagonal form of symmetric matrix of contact probabilities and visualized by structural indicatrices – 2nd order surfaces. A consistent nomenclature of petrographic structures has been proposed. Earlier the method showed itself well in describing the structures of ijolites and urtites of the Khibiny Mountains, as well as amphibolites of the islands of Keretsky Archipelago (the White Sea). Mass application of the method is restrained by the routine procedure of calculating the probabilities of intergranular contacts in petrographic thin sections under a microscope. The problem of modern optical structure analyzers is assignment different sections of the same anisotropic mineral to different minerals, and separation blocks of a mineral individual to different individuals. The paper describes the experience of using the domestic MIU-5M device for scanning petrographic thin sections by the linear method of Rosival. The combination of visual control and minimum automation of the process allows us to achieve convergence of the structural types with results obtained by manual processing of image of petrographic thin section. Additionally, thin sections have been studied, for which the structural types differ with various methods of counting. It has been revealed that the presence of poikilitic ingrowths and features of the mineral composition (the existence of hypergene changes or minerals with similar optical properties) affect the statistics of probabilities. Recommendations are given on the selection of the scanning step depending on the grain size in the studied rock.
(in Russian, стр.7, fig. 4, tables. 0, ref 10, AdobePDF, AdobePDF 0 Kb)
Vol. 25 (2022 year), No. 1, DOI: 10.21443/1560-9278-2022-25-1
Neradovsky Yu. N., Miroshnikova Ya. A., Companchenko A. A., Chernyavsky A. V.
About terraces on the shore of the Teriberskaya Bay of the Barents Sea (the Kola Peninsula)
The paper considers the results of the study of modern terraces on the coast of the Lodeyny Peninsula in the Barents Sea. According to field observations, decoding of space and geodetic maps and volumetric modeling, signs of three terraces have been identified. Two terraces having a rear seam, a cliff, a brow and horizontal platforms have been studied in more detail. The rear seams are located at 7 and 30 m, and the edges at 10 and 40 m above the sea level. The third terrace is confined to the level of 40–60 m, and has not been studied in detail. According to estimates, the first two terraces were formed about 3,300 and 6,000 years ago respectively. The 1st terrace characterizes the period of slow land rise by 10 m, at the speed up to 3 mm/year, which began about 3,300 years ago and continues to the present. It is characterized by a uniform sea retreat of about 15 mm/year. The erosion products of this terrace are common in the lateral zone and represent modern marine sediments, including beaches forming a new terrace. The 2nd terrace characterizes to the dynamics of rapid land rise by 30 m at a speed of about 11 mm/year, which occurred in the period from 6,000 to 3,300 years ago. The erosion products of this terrace are most common on the coast and are found at a distance of 100 m to 2–3 km from the shore. It is assumed that the speed of movement of the coastline during the retreat of the sea was different and reached up to 900 mm/year. According to the authors, preliminary data indicate the instability of the territory and the manifestation of block movements, which may have a negative impact on the development of infrastructure.
(in Russian, стр.12, fig. 14, tables. 0, ref 17, AdobePDF, AdobePDF 0 Kb)
Vol. 26 (2023 year), No. 2, DOI: 10.21443/1560-9278-2023-26-2
The paper presents the results of studying the Riphean red-colored sandstones of the Tersky coast of the White Sea. 21 structural elements characterizing the conditions of rock formation have been considered, including 15 ancient and 6 modern deposits. Observations were carried out for 10 years in two areas of the White Sea coast. The purpose of the research is to establish the reasons for the absence of organic matter, the origin of the hematite admixture in the Riphean sandstones, and to assess the climatic conditions during their formation. These issues are key to identifying the Proterozoic red formation. The data have shown that some rock structures are similar in ancient and modern deposits. Such structures include, for example, wave ripples repeating in detail the dimension, shape, and orientation in both epochs, and therefore can be used to assess ancient marine sedimentation conditions. However, most of the structures testify to fundamental differences in the conditions of rock formation. It has been established that takyrs were systematically formed in ancient rocks and hematite was deposited, which indicates the arid climate in the Riphean and the specific composition of sea water. The most important difference between ancient deposits is the absence of fauna and flora in them.
(in Russian, стр.11, fig. 8, tables. 0, ref 15, AdobePDF, AdobePDF 0 Kb)