Moscow University Geology Bulletin最新文献

Abstract

A three-dimensional resistivity model is presented that contains electrical resistivity anomalies of a complex shape on three structural levels: in the sedimentary cover, in the consolidated crust, and in the upper mantle. The synthetic (model) magnetotelluric data obtained as a result of solving the direct problem are analyzed to identify anomalies associated with resistivity in inhomogeneities at different depths. Quantitative estimates of the sensitivity of various components of the magnetotelluric data to these inhomogeneities are given. Further, we plan to use the presented data to evaluate the efficiency of various methods for solving inverse problems.

Abstract—The geochemical and lithological features of bacterial–algal structures from the top of the Abalak and Georgia Formations in the central part of Western Siberia were studied in order to determine the specific conditions of their formation. The authors compared the element composition of these microbial carbonates with the secondary carbonate rocks of the Abalak and Georgia formations. According to the results of X-ray fluorescence analysis, differences were identified in the contents of MnO, Cr, V, Ni, Cu, and Zn in two types of carbonates. The higher content of MnO in bacterial–algal structures were explained by the ability of bacteria to sorb Mn on the surface of their cells. This process requires oxygen, which suggests the presence of a natural aerobic environment for the development of bacteria during the period of sediment accumulation. According to the results of the study of microbial carbonates under a scanning electron microscope, it was revealed that Mn, for the most part, is concentrated in carbonate minerals, in particular in kutnohorite. The increased content of biophilic elements such as Ni, Cu, Zn, V in microbial carbonates, is probably associated with the transformation of humic organic matter, that was accumulated in shallow water environments and was actively recycled by microbial organisms. Minerals with the high Ba concentration were also found in isolated bacterial–algal structures. According to the authors, such single barium mineralization could be caused by the point effect of both near-surface and deep-seated barium-containing solutions and are not associated with an increased content of manganese in the studied deposits.

Abstract

The results of density modeling of the tectonosphere structure in the Antarctic sector of the South Atlantic Ocean are presented. The modeling was carried out along the profiles stretching from the Falkland Plateau to the Mozambique Ridge and crossing a series of submarine rises and ridges separated by deep-sea basins. Studies show that the crust of this region has a heterogeneous structure and the crust underlying the rises is of a different structure, indicating different origins of the respective rises.

Abstract—

The issues of developing a general classification of geological processes that are the subject of research in modern engineering geodynamics, one of the areas of engineering geology, are considered. A new general classification of geological processes for the purposes of engineering geology is proposed, taking into account the disadvantages of previous similar classifications and covering the whole variety of both natural geological processes and their technogenic analogues, that is, engineering-geological processes.

Abstract

A set of methods (seismoacoustic profiling, analysis of continuous borehole sections, stratigraphic studies on malacofauna, and radioisotope age dating) was used to identify the Novocaspian, Mangyshlakian, Khvalynian, Atelian, Hyrkanian, and Upper Khazarian horizons in the Upper Quaternary deposits of the Northern Caspian shelf. Based on AMS radiocarbon and uranium-thorium dating, the time of their accumulation is determined, respectively, in the intervals of 0 to 8.5, 8.5 to 13, 13 to 50/60, 50 to 70, >60 to 120 and more than 120 000 years ago.

Abstract

The general characteristics of the Zun-Ospa gold deposit and the mineral composition of ores are presented. Based on mineralogical studies two stages of mineralization have been established: the first (hydrothermal) stage, which was divided into four substages and the second (hypergenic) one. The microprobe data on the mineral phases that make up the ores of the deposit are presented. Gold of two generations, which are different both in composition and associations, has been described.

Abstract

This paper presents the results of an isothermal kinetic experiment by closed-system hydrous pyrolysis using an oil source rock sample from the Bazhenov shale formation. After 48 hours of thermal exposure at a temperature of 350°C, 80% of the kerogen generation potential with respect to the initial sample was transformed into hydrocarbons. Changes in organic matter during laboratory modeling of maturation controlled by pyrolytic parameters, follow the same trends as changes in natural source rocks at different katagenesis stages. The kinetic spectra of kerogen activation energy destruction show a certain heterogeneity of organic matter inside the rock. A decrease in low-energy bonds and an increase in the maximum release of hydrocarbon compounds from 53 to 54 kcal/mol were observed at a constant frequency factor. The calculated changes in the generation of hydrocarbon compounds at different activation energies depending on the maturity level show differences from the experimental results, which indicates the influence of the maceral composition and the necessity to take the variability of individual components into account in basin modeling.

Abstract

The results of a comprehensive study of the Lower–Upper Ypresian boundary sediments at the Suvlu-Kaya Mountain section (Bakhchisarai region, Southwestern Crimea) are presented. The evolution of formation of the nummulitic bank in the study area is shown based on a detailed microfacies analysis. The sediments were formed on a deep shelf with depths at and below the storm wave base. It has been established that the Ypresian transgression was developed gradually, in three stages, with the maximum at the end of the Early Ypresian, and then was followed by a long-term regression. The data are confirmed by the results of the micropaleontological analysis of the morphogroups.

Abstract

The solubility of crystalline and precipitated calcium fluoride in seawater and brines of the first stages of its evaporative concentration (before the beginning of gypsum and halite setting) has been experimentally studied. It is established that in the entire studied range of salinity, seawater and its derivatives are strongly undersaturated in calcium fluoride, which excludes its spontaneous precipitation in drying isolated sea basins. A necessary condition for the formation of sedimentary fluorite is the entry of significant amounts of dissolved fluorine from external sources, which can be river runoff, volcanic emanations, and hydrothermal solutions, into drying sea basins.

Abstract

This paper presents the results of seismic monitoring for the major seismoactive regions of Russia in 2022: Caucasus, East European Platform, Arctic, Altai and Sayan, Cis-Baikalian, and Transbaikalian regions; the Amur region and Primorye; Sakhalin Island, Kuril–Okhotsk region, Yakutia, Northeast Russia, and Chukotka, Kamchatka, and Commander Islands. For each region, the catalogs of the most significant and tangible earthquakes are given with the hypocentral parameters and magnitudes as obtained from the instrumental observations. The macroseismic effects from the majority of tangible earthquakes (with I ≥ 2.5 on the ShSI-2017 scale) that occurred in the territory of Russia have been analyzed. The materials presented in this work are of value for specialists in the fields of seismology and seismotectonics. The article also assists in early familiarization of interested readers with the available general information about the seismicity of Russia in 2022 before the release of full-scale special publications devoted to earthquakes in Russia.