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Russian Geology and Geophysics

2018 year, number 4

1.
STRUCTURE OF THE BASEMENT SURFACE AND SEDIMENTS IN THE KOCHKOR BASIN (Tien Shan): GEOLOGICAL AND GEOPHYSICAL EVIDENCE

E.S. Przhiyalgovskii1, E.V. Lavrushina1, V.Yu. Batalev2, E.A. Bataleva2, M.G. Leonov1, A.K. Rybin2
1Geological Institute, Russian Academy of Sciences, Pyzhevsky per. 7, Moscow, 119017, Russia
2Research Station, Russian Academy of Sciences, Bishkek, Kyrgyzstan
Keywords: Пластические деформации, поверхность фундамента, детачмент, магнитотеллурическое зондирование, Кочкорская впадина, Тянь-Шань, Ductile deformation, basement surface, detachment fault, magnetotelluric soundings, Kochkor basin, Tien Shan

Abstract >>
The basement surface and sediments of the Kochkor basin have been studied by structural geological and geophysical methods. The work included high-resolution mapping of the southern basin margin, with a focus on Cenozoic basin stratigraphy, structural unconformities, basement/sediment contacts, and latest deformation (folds, fractures, and faults). Magnetotelluric (MT) soundings provided insights into basin and basement structure, especially important in the poorly exposed eastern flank of the basin margin. The sections across the southern margin of the basin based on geological and geophysical data reveal deformation in both the basement and the sediments. Deformation in sediments shows up as folding, conformal peneplain surfaces, large faults, low-angle detachment faults, and related thrust-fold belts. Thrusting in sediments is inferred to result from cataclastic flow and mass redistribution in disintegrated basement granites. With this mechanism, the total amount of thrusting in the central part of the basin can exceed the convergence of the basin sides.



2.
PALEOEARTHQUAKES IN THE UIMON BASIN (Gorny Altai)

E.V. Deev1,2, I.D. Zol’nikov3,2, I.V. Turova1,2, G.G. Rusanov4, Yu.M. Ryapolova1,2, N.N. Nevedrova1,2, S.A. Kotler3
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
4OAO “GornyAltai Survey Group,”, ul. Sovetskaya 15, Maloeniseiskoe Village, Altai Territory, 659370, Russia
Keywords: Палеосейсмология, первичные и вторичные сейсмодислокации, сильные древние землетрясения, Уймонская впадина, Горный Алтай, Paleoseismology, primary and secondary seismic deformations, large paleoearthquakes, Uimon basin, Gorny Altai

Abstract >>
Paleoseismological studies confirm that the Uimon basin is thrust by its northern mountain border over the sediments along the active South Terekta fault. The latest motion along the fault in the 7-8th centuries AD induced an earthquake with a magnitude of Mw = 7.4-7.7 and a shaking intensity of I = 9-11 on the MSK-64 scale. The same fault generated another event ( M ≥ 7, I = 9-10), possibly, at ~16 ka, which triggered gravity sliding. The rockslide dammed the Uimon valley and produced a lake, where lacustrine deposition began at ~14 ± 1 ka, and a later M ≥ 7 ( I = 9-10) earthquake at ~6 ka caused the dam collapse and the lake drainage. Traces of much older earthquakes that occurred within the Uimon basin are detectable from secondary deformation structures (seismites) in soft sediments deposited during the drainage of a Late Pleistocene ice-dammed lake between 100 and 90 ka and in ~77 ka alluvium. The magnitude and intensity of these paleoearthquakes were at least M ≥ 5.0-5.5 and I ≥ 6-7.



3.
FLUORINE AND CHLORINE IN APATITES, MICAS, AND AMPHIBOLES OF LAYERED TRAP INTRUSIONS OF THE SIBERIAN PLATFORM

V.V. Ryabov1, O.N. Simonov2, S.G. Snisar2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Polar Division of Public Joint Stock Company “Mining and Metallurgical Company “Norilsk Nickel”, Gvardeiskaya pl. 2, Norilsk, Krasnoyarsk Territory, 663330, Russia
Keywords: Траппы, расслоенные интрузии, геохимия галогенов, апатит, слюда, амфибол, Сибирская платформа, Traps, layered intrusions, geochemistry of halogens, apatite, mica, amphibole, Siberian Platform

Abstract >>
Geochemistry of chlorine and fluorine in apatites, micas, and amphiboles in rocks from eight intrusive complexes of the Siberian Platform has been first studied on the basis of new factual and analytical data (more than 1000 analyses). The main attention is focused on minerals from layered intrusions. Most apatites show F > Cl; the maximum contents of halogens are specific to chlorapatite (6.97 wt.% Cl) and fluorapatite (6.04 wt.% F). The total f value (f = Fe/(Fe + Mg), at.%) of femic minerals varies from 2 to 98 at.% in micas and from 22 to 95 at.% in amphiboles. The Cl-f and F-f trends show an increase in the Cl content and a decrease in the F content in the minerals with increasing f. Chlorine clearly exhibits ferrophilic properties, and fluorine has magnesiophilic properties. The halogen-richest minerals are fluorophlogopite (F = 7.06 wt.%, f = 7 at.%), chlorannite (Cl = 6.30 wt.%, f = 89 at.%), and chloroferrihastingsite (Cl = 5.22 wt.%, f = 90 at.%). Coexisting micas and amphiboles in the rocks are close in f value, but the micas are richer in Cl than the amphiboles. We assume that the halogen-containing minerals crystallized at the high pressure of halogen-hydrocarbon fluids at the levels of the MW, IW, and QIF buffers. The reducing conditions of the magmatism process are also evidenced by the presence of graphite and native metals in the rocks. The similarity of the Cl-f and F-f trends of micas and amphiboles from different intrusive complexes indicates the same mechanisms of the melt differentiation and mineral crystallization.



4.
THERMODYNAMIC MODEL OF FORMATION OF CARBONATES AND URANIUM MINERAL PHASES IN LAKES NAMSHI-NUR AND TSAGAN-TYRM (Cisbaikalia)

V.D. Strakhovenko1,2, O.L. Gas’kova1,2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Донные отложения озер, минералогия и геохимия аутигенных карбонатов, минеральные фазы урана, термодинамическое моделирование, Прибайкалье, Bottom deposits of lakes, mineralogy and geochemistry of authigenic carbonates, mineral phases of uranium, thermodynamic modeling, Cisbaikalia

Abstract >>
The Tazheran lakes are located compactly in the small Tazheran steppe area. Their bottom sediments are predominantly various calcite-dolomite carbonates, and their waters are rich in uranium. The studies have shown that the main process in these lakes is chemogenic carbonate precipitation with the participation of carbon dioxide formed through the bacterial destruction of organic matter. For thermodynamic modeling of the composition of bottom sediments, we chose two lakes with different basic parameters. Calculations were made for the 15-component heterogeneous system H2O-Na-Ca-Mg-K-Sr-Ba-Si-Al-Cl-C-S-Fe-U-Mn including particles in the solution, minerals, and gases at 25ºC and 1 bar. As starting information, we used the obtained analytical data on the natural composition of waters and bottom sediments. The results show that calcite-dolomite carbonates are predominant in the bottom sediments and the destruction of organic matter results in reducing conditions. This confirms the hypothesis of the formation of mineral phases of U(IV) during diagenetic processes in the bottom sediments of the studied lakes.



5.
BIOGEOCHEMISTRY AND MICROFOSSILS OF THE UPPER JURASSIC AND LOWER CRETACEOUS, ANABAR BAY, LAPTEV SEA

V.A. Kashirtsev1,2, B.L. Nikitenko1,2, E.B. Peshchevitskaya1, E.A. Fursenko1,2
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Юра и мел, органическая геохимия, молекулы-биомаркеры, микробентос, палиноморфы, палеообстановки, Арктика, море Лаптевых, Arctic, Laptev Sea, Jurassic and Cretaceous, organic geochemistry, biomarker molecules, microbenthos, palynomorphs, paleoenvironments

Abstract >>
A detailed analysis of organic matter from the Oxfordian-Lower Valanginian interval of the Nordvik section (Anabar Bay) allows the definition of three geochemical horizons (terpane, diasterene, and hopane), which are characterized by specific geochemical compounds and their ratios. These horizons are correlated with several stages in the evolution associated with ecological and geochemical changes in sea paleobasin. Our study shows a good correlation among the variation in many geochemical parameters, the composition of microfossil assemblages, and the transgressive-regressive phases of the paleobasin evolution. Moderately shallow-water facies was reconstructed using micropaleontological, palynological, and lithological data from the upper and lower parts of the section, where the terpane and hopane horizons were identified. Both horizons are characterized by a general dominance of hopanes over other polycyclic biomarkers and the presence of compounds with the biological configuration and organic matter of mixed terrestrial-marine origin, including the presence of benzohopanes and retene, an indicator of the conifer resins. This is also reflected in the composition of palynological assemblages, which are dominated by terrestrial palynomorphs, with rare conifer pollen grains. Relatively deep-water facies were identified in the middle part of the section (diasterene horizon). A distinctive geochemical feature of this interval is high relative abundances of diasterenes and 4-methyldiasterenes. The lower subhorizon is characterized by the highest values of the pristane/ n -C17 ratio and relatively light 13C values of noncarbonate carbon. The aromatic fractions have anomalously high concentrations of methyltrimethyltridecylchromans (MTTCs), which are interpreted to be derived mostly from chlorophyll of prasinophytes. The terpenoid distribution is marked by the presence of neohop-13(18)-enes, which probably originated from the activity of methanotrophic bacteria. The above geochemical parameters indicate high photic zone productivity (which is confirmed by the composition of palynological assemblages with abundant dinocysts and prasinophytes) that favored the accumulation of organic matter in dysaerobic conditions, which periodically occurred in the bottom of paleobasin. The alternation of dysaerobic and low-oxic bottom water conditions is easily reconstructed from the analysis of microbenthic communities. The analysis of biogeochemical, micropaleontological, paleontological, and palynological data on the Upper Volgian-lowermost Boreal Berriasian organic-rich shales revealed a very good source rock potential for this part of the section, as indicated by relatively high concentrations of organic matter of mixed bacterial-algal genesis and stagnant conditions during deposition and diagenesis. However, this potential was not realized because of the extremely mild thermobaric conditions that existed within the Mesozoic strata of the present-day Anabar Bay. At the same time, our results and analysis of the available data allow an optimistic assessment of the hydrocarbon potential of Jurassic-Lower Cretaceous deposits on the Laptev Sea shelf.



6.
CHARACTERISTICS OF HYDROTHERMAL-STRUCTURE-CONTROLLED FRACTURE-VUG DOLOMITE RESERVOIR AND ITS INFLUENCE ON OIL-WATER DISTRIBUTION: А CASE STUDY ON THE LOWER CRETACEOUS, BAIYINCHAGAN SAG, ERLIAN BASIN, NORTH CHINA

Zhicheng Lei1, Wangshui Hu2, Huaimin Xu1, Bo Xu3, Chun Cao4, Chao Cheng3, Qulei Zhu1
1College of Geoscience, China University of Petroleum-Beijing, Beijing, China
2College of Geoscience, Yangtze University, Wuhan, Hubei, China
3CNOOC China Co., LTD. Shanghai branch development production, Shanghai, China
4CNOOC EnerTech-Drilling&Production Co, Data Processing Co. Zhanjiang, Guangdong, China
Keywords: Гидротермальный доломит, трещинно-полостной коллектор, распределение нефти и воды, Северный Китай, бассейн Эрлиан, Hydrothermal dolomite, fracture-vug reservoir, oil-water distribution, North China, Erlian Basin

Abstract >>
Fractures and vugs were used as the primary dolomite reservoir space in the study area, which improved the reservoir’s physical properties and influenced the distribution pattern of oil and water that were developed in the Upper Tenger Formation, Lower Cretaceous, Baiyinchagan sag, Erlian Basin. Based on the core observation data, thin slice analysis, and image logging, the cave-fractured reservoir was primarily developed in the actic region near the side of a depositional fault. Tectonic and diagenetic fractures were the primary types of fractures. High-angle tectonic fractures in the closure and open status were developed well in dolomitic mudstone, while a low-angle fracture and reticulate fractures were developed in the tectonic-hydrothermal hybrid process and were filled with hydrothermal minerals. The reservoir was located in low-lying land; therefore, detrital grain pressolution fractures were formed by burial diagenesis. Intergranular and intrangranular dissolved pores, which were formed by hydrothermal activity, were developed primarily in the highly dolomite lithology. According to the diagenesis temperature of dolomite from a carbon-oxygen isotope analysis, multiple hydrothermal fluid injection events occurred, and dolomitization ensued before massive hydrocarbon migration. The dissolution of organic acids formed by hydrocarbon charges after dolomitization and inorganic acid produced by burial diagenesis for soluble minerals effectively promoted the reservoir properties. Strong heterogeneity due to lithology and fracture-vug systems led to intricate oil-water relationships. Four statuses occurred, including cave-fracture oil, isolated oil, stored oil, isolated water, and stored water. The oil-water distribution patterns were established based on the core observation.



7.
STRUCTURE OF THE ZEYA BLOCK OF TOKIN STANOVIK according to RESULTS OF MAGNETOTELLURIC SOUNDING

V.B. Kaplun
Yu.A. Kosygin Institute of Tectonics and Geophysics, Far East Branch of the Russian Academy of Sciences, ul. Kim Yu. Chena 65, Khabarovsk, 680000, Russia
Keywords: Магнитотеллурические зондирования, глубинное строение, Сибирская платформа, Становой разлом, Magnetotelluric soundings, deep structure, Siberian Platform, Stanovoi fault

Abstract >>
The paper describes the results of magnetotelluric sounding (MTS) carried out in the Zeya block of the Stanovoi megablock, in the area of its junction with the Aldan Shield. The border between them runs along the Stanovoi fault. Based on the results of interpretation of MTS curves and the gravity, magnetic, and geological data, the geological/geophysical sections have been constructed to a depth of 7 km along two ~20 km long profiles running across the Stanovoi fault. About 1 km thick and approximately 2 km long conductivity zone has been distinguished beneath the Okonon plateau of Quaternary basalts with electrical resistivity of less than 100 Ohm·m. This anomaly is associated with ore mineralization confined to Early Proterozoic gabbro intrusion. A 3D density modeling was performed. The northeastern dip of high-density bodies to a depth of 25 km is observed at the northwestern strike in the area of the Okonon basalt plateau.



8.
MAGNETIC MEASUREMENTS IN ELECTRICAL PROSPECTING BY RESISTIVITY METHODS

V.S. Mogilatov1,2, N.O. Kozhevnikov1,2, A.V. Zlobinskii3
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3ZaVeT-GEO, ul. Voskhod 26/1, office 56, Novosibirsk, 630102, Russia
Keywords: Электроразведка, методы сопротивлений, магнитное поле, DC, MMR, MIP, круговой электрический диполь, Electrical prospecting, resistivity methods, magnetic field, DC, MMR, MIP, circular electric dipole

Abstract >>
The electrical resistivity and induced polarization (IP) methods are widely used in geological mapping, prospecting and exploration of mineral deposits, engineering geology, hydrogeology, archaeology, and geotechnical and environmental applications. Historically, these methods have formed the basis of the electrical prospecting technique. In these methods, a DC or low frequency AC electrical current is introduced into the earth through a grounded transmitter circuit. The measured quantity is the electric field. However, if the earth’s resistivity or chargeability changes horizontally, this change gives rise to an anomalous magnetic field, which is studied by the magnetometric resistivity (MMR) and magnetic induced polarization (MIP) methods, respectively. Along with advantages, some shortcomings are inherent in the MMR and MIP techniques. Apparently, the main drawback of these methods is that the magnetic fields of both transmitter circuit wire and ground electrodes on the surface are several orders of magnitude greater than the anomalous magnetic field response. This introduces a significant «noise» to magnetic-resistivity data. We investigate the potential of using the circular electric dipole (CED) in magnetometric resistivity techniques. It has been found that application of a CED, instead of a conventional transmitter circuit, dramatically enhances the signal-to-noise ratio.



9.
REQUIREMENTS FOR THE PERFORMANCE OF A GROUND-PENETRATING RADAR SYSTEM IN SEARCHING FOR CAVITIES

L.B. Volkomirskaya, O.A. Gulevich, V.V. Varenkov, V.I. Sakhterov
N.V. Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation, Russian Academy of Sciences, Kaluzhskoe shosse 4, Troitsk, Moscow, 108840, Russia
Keywords: Георадар, поиск пустот, поиск полостей, технические характеристики георадара, георадиолокация, динамический диапазон, Ground-penetrating radar, cavity mapping, search for cavities, GPR performance, GPR survey, dynamic range

Abstract >>
The requirements for the performance of a ground-penetrating radar (GPR) system for detecting subsurface cavities are analyzed by numerical modeling of the GPR problem. The algorithm used to solve the forward GPR problem is approximated to a real experiment with regard to the design of the GPR system, the parameters of the source and receiver, and their position relative to the medium under study and its inhomogeneity. We calculated the spatiotemporal distribution of the field of the detected signal from a pulse source located at the interface between the medium and a cavity anomaly of a given geometry. The results were used to estimate the dynamic range of the GPR system necessary for determining the anomaly. We also performed GPR surveys of low-contrast inhomogeneities (cavities in mines) using GROT 12 GPR systems and analyzed the survey results by numerical modeling. It is shown that the GPR performance required to detect and locate inhomogeneities of interest at a certain sounding depth can be estimated in the experiment design phase.



10.
DISPERSION OF GROUP VELOCITIES OF RAYLEIGH AND LOVE WAVES AND ANISOTROPIC PROPERTIES OF THE ASIAN CONTINENT

A.I. Seredkina, V.M. Kozhevnikov, O.A. Solovei
Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
Keywords: Волны Рэлея, волны Лява, групповые скорости, поверхностно-волновая томография, вертикальная анизотропия, азиатский континент, Rayleigh and Love waves, group velocities, surface wave tomography, vertical anisotropy, Asian continent

Abstract >>
We have studied the structures of the Earth’s crust and upper mantle of the Asian continent using a representative sample of dispersion curves of group velocities of fundamental-mode Rayleigh and Love waves for more than 3200 seismic paths. Maps of distribution of variations in group velocities with periods of 10 to 250 s over a spherical surface were compiled by the 2D tomography method. The maps reflect the deep structure of the Earth’s crust and upper mantle of the study area and give a tentative idea of the horizontal distribution of the anisotropic properties of the mantle matter. The obtained data are confirmed by the calculations of the velocity profiles of SV and SH waves for the entire Asian continent and for its regions. Vertically, anisotropy is observed to depths of ~250 km, with its maximum in the depth range from the bottom of the crust to 150 km.