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Russian Geology and Geophysics

2021 year, number 2

1.
A NEW INDICATOR OF THE MATURITY OF ORGANIC MATTER FROM DOMANIK DEPOSITS

N.S. Burdel'naya, D.A. Bushnev
Institute of Geology, Komi Research Center, Ural Branch of the Russian Academy of Sciences, ul. Pervomaiskaya 54, Syktyvkar, 167982, Russia
Keywords: Domanik deposits, aromatic biomarkers, catagenesis, 1,2,8-trimethylphenanthrene, 1,1,7,8-tetramethyl-1,2,3,4-tetrahydrophenanthrene, Timan-Pechora petroleum province

Abstract >>
Study of the aromatic fraction of Late Devonian oils and organic matter from domanik deposits of the Timan-Pechora petroleum province has revealed compounds whose proportion depends on the degree of OM transformation, namely, 1,1,7,8-tetramethyl-1,2,3,4-tetrahydrophenanthrene (1,1,7,8-TMHP) and 1,2,8-trimethylphenanthrene (1,2,8-TMP). It has been established that 1,1,7,8-TMHP dominates over 1,2,8-TMP in the immature OM; as the thermal maturation of OM increases, 1,2,8-TMP begins to prevail. The same pattern is observed for the Late Devonian oils. An increase in the ratio of 1,2,8-TMP to 1,1,7,8-TMHP with the growing thermal maturation of OM and the transition of one compound into another permit using this ratio as an additional indicator of OM maturity in domanik rocks.
																								



2.
GEOLOGICAL IMPLICATIONS FOR GAS SATURATION OF BOTTOM SEDIMENTS IN SEDIMENTARY BASINS IN THE SOUTHEASTERN SECTOR OF THE EAST SIBERIAN SEA

A.I. Gresov, A.V. Yatsuk
V.I. Ilichev Pacific Oceanological Institute, Far Eastern Branch of the Russian Academy of Sciences, ul. Baltiiskaya 43, Vladivostok, 690041, Russia
Keywords: Sedimentary basin, geologic structure, bottom sediments, gas composition, geochemical parameters of gas, genesis, gas sources, gas saturation, geologic factors, East Siberian Sea

Abstract >>
We present research results for the geologic structure of the De Long, Aion, and Pegtymel sedimentary basins of the East Siberian Sea. The materials of geological surveys and drilling in their land area and island surroundings, the data obtained from geophysical surveys conducted by Dalmorneftegeofizika, MAGE, and Sevmorgeologiya, and the seismic and deep drilling data on the U.S. sector of the Chukchi Sea are summarized and analyzed. Pre-Paleozoic strata and the sedimentary cover have been identified throughout the sections of the sedimentary basins, which suggests the existence of a geologic cover-basement boundary rather than an arbitrary called acoustic basement horizon. The data on the geologic structure and gas saturation of the upper parts of the sedimentary sections were obtained during the study and gas-geochemical testing of core samples and bottom sediments from coastal shallow wells and corers. Gas contained in the rocks and bottom sediments in the study area includes hydrocarbon gases (HCGs) (4, 2-5, and their unsaturated homologues), 2, 2, , N2, Ar, and, seldom, CO and H2S. The data on gas saturation of bottom sediments and the geochemical parameters of their syngenetic and epigenetic gases are presented. Areas of abnormal saturation of sediments with CO2, 4, other HCGs, H2, and He (>5, 0.05, 0.001, 0.005, and 0.005 cm3/kg, respectively) have been identified, and maps of the gas saturation patterns in bottom sediments have been compiled. It is established that both gas saturation and distribution are determined mainly by the geologic evolution, tectonics, magmatism, geocryologic conditions, lithologic composition, catagenesis, coal content, bituminosity of sedimentary rocks, and oil and gas potential of the study area.
																								



3.
PREDICTION OF OIL AND GAS OCCURRENCE IN THE JURASSIC RESERVOIRS OF THE ZONE OF JUNCTION OF THE YENISEI-KHATANGA AND WEST SIBERIAN BASINS

D.A. Novikov1,2, E.V. Borisov1
1Trofimuk 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 1, Novosibirsk, 630090, Russia
Keywords: Prediction of oil and gas occurrence, Jurassic reservoirs, poroperm properties, oil and gas hydrogeochemistry, oil and gas criteria, hydrogeochemical anomalies, Yenisei-Khatanga regional trough, West Siberia, Arctic

Abstract >>
Based on a comprehensive analysis of the geologic structure, hydrogeology, and hydrogeochemistry, we predict oil and gas occurrence in the Jurassic reservoirs of the zone of junction of the Yenisei-Khatanga and West Siberian basins. We have established the regularities of formation of sandstones of the Sigovaya, Malyshevka, Vym, Nadoyakha, Sharapovka, and Zima reservoirs and examined their poroperm properties. The studied Lower and Middle Jurassic deposits, beginning from the Malyshevka reservoir, are characterized by abnormally high formation pressures with an anomaly ratio of up to 1.92. The Jurassic reservoirs bear weakly alkaline, moderately brackish to slightly saline groundwater of Cl Na, Cl-HCO3 Na, and HCO3-Cl Na compositions with TDS = 3.0-23.3 g/dm3. The low-mineralization connate waters determine an inverse vertical hydrogeochemical zoning in the sedimentary cover of the study region. The research data show favorable conditions for the generation and accumulation of hydrocarbon pools. It is shown that the main criteria for oil and gas occurrence are hydrogeochemical (contents of organic compounds, NH4, B, I, Br, naphthenic acids, and benzene; B/Br and HCO3/Cl coefficients), gas (total gas saturation of formation waters, degree of their gas saturation (Kg), and composition of water-dissolved gases), and hydrodynamic (formation pressures and their anomaly ratio (Ka)) indicators. Also, complex anomalies have been revealed in the Jurassic deposits, which trace the gas fields and revealed oil and gas occurrences. The Jurassic reservoirs are most promising for structure-lithologic traps in the peripheral zones of the basin and on the slopes of large positive structures. The Middle Jurassic deposits in the interior of the Yenisei-Khatanga Basin, poorly studied by deep drilling, might also be of interest as potential hydrocarbon pools.
																								



4.
THE ORIGIN OF TERRACES IN BURIED VALLEYS IN THE NORTHWEST OF THE EAST EUROPEAN PLAIN

N.V. Karpukhina1, S.S. Bricheva1,2, E.A. Konstantinov1, O.M. Tatarnikov3, A.N. Makkaveev1, A.L. Zakharov1
1Institute of Geography of the Russian Academy of Sciences, Staromonetnyi per. 29, Moscow, 119017, Russia
2Lomonosov Moscow State University, Leninskie Gory 1, Moscow, 119991, Russia
3Pskov State University, pl. Lenina 2, Pskov, 180000, Russia
Keywords: Buried valleys, denudation terraces, karst, glacial erosion, northwest of the East European Plain

Abstract >>
The paper considers the origin of terraces that often complicate the slopes of abnormally deep buried valleys in the northwest of the East European Plain. The Izborsk-Maly valley (Pskov Region, Russia), which is half filled with Quaternary sediments, was chosen as the object of study. Since the upper part of the valley remains unfilled, it is possible to study in detail both geologic and geomorphologic structures of its terraced slopes being of particular interest in the context of the origin of buried valleys and the role of substrate in it. The four denudation-terrace levels that have been identified on the slopes of the Izborsk-Maly valley at absolute elevations of 53, 56-58, 70-72, and 75-77 m formed during the destruction of the preglacial karst landscape under the influence of Pleistocene glaciations. The formation of the terraces was linked probably with several stages of overdeepening of the valley and its expansion by the glacial erosion processes, which corresponded to at least two stages of the ice sheet advance in this area. The last stage may have been the beginning of the Late Valdai (Weichselian) glaciation or the activation of the edge of an ice sheet during its Luga phase (~15.7 cal kyr BP). Results of the study suggest that the Izborsk-Maly valley formed in subglacial conditions. The degree of glacial erosion was determined primarily by the coherence of Devonian carbonate-terrigenous rocks hosting the valley and the degree of the area transformation by karst processes. The cirque shape of slopes is the evidence of karst processes expression in pre-glacial time. Analysis of literature data shows that the origin of denudation terraces in the buried valleys in the northwest of the East European Plain has been paid little attention. The obtained data contribute to the study of this problem and provide insights into the origin of buried valleys.
																								



5.
CAUSES OF THE OCCURRENCE OF -TYPE VOLCANIC ROCKS IN ACTIVE CONTINENTAL MARGINS (southern Sikhote-Alin, Russian Far East)

A.V. Grebennikov, S.O. Maksimov
Far East Geological Institute, Far Eastern Branch of the Russian Academy of Sciences, pr. 100-letiya Vladivostoka 159, Vladivostok, 690022, Russia
Keywords: -type igneous rocks, fluidal magmatic differentiation, Campanian, Sikhote-Alin

Abstract >>
New isotope-geochemical data on the volcanic complexes of the South Yakut and Martel volcanic depressions in southern Primorye are presented. Their formation in the early Eocene (54.3 Ma) and Late Cretaceous (83.5 Ma), respectively, is evidenced by U-Pb zircon dating (LA-ICP-MS). Based on the geochemical characteristics, it is concluded that the volcanics are typical A -type igneous rocks. Their formation coincides with the sudden change in the vector of motion of the Pacific slab with respect to the continent in the Campanian and Paleocene-Eocene, which caused destruction of the slab with its probable discontinuity and the injection of the subslab asthenosphere. The effect of mantle fluids on the continental lithospheric-rock melting determined the generation of magmas with the specific geochemical features of A -type igneous rocks. The regularities of their composition are due to the deep-seated reduced F-rich fluids that caused the intense differentiation of magmas accumulating fluidized melts enriched in mobile components in the apical part.
																								



6.
AN AWAKENING MAGMATIC SYSTEM BENEATH THE UDINA VOLCANIC COMPLEX (Kamchatka): EVIDENCE FROM SEISMIC UNREST OF 2017-2019

Yu.A. Kugaenko1, V.A. Saltykov1, I.Yu. Koulakov2,3, V.M. Pavlov1, P.V. Voropaev1, I.F. Abkadyrov1,4, V.P. Komzeleva2
1Geophysical Survey of the Russian Academy of Sciences, Federal Research Center, bulv. Piipa 9, Petropavlovsk-Kamchatsky, 683006, Russia
2Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
3Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090, Russia
4Institute of Volcanology and Seismology, Far Eastern Branch of the Russian Academy of Sciences, bulv. Piipa 9, Petropavlovsk-Kamchatsky, 683006, Russia
Keywords: Seismic activity, seismicity, volcano, magmatic system, Bolshaya Udina and Malaya Udina volcanoes, seismic tomography, long-period earthquakes

Abstract >>
The Udina volcanic complex located in the southeastern part of the Klyuchevskoy group of volcanoes in Kamchatka remained dormant for several thousand years, but the magmatic system beneath the area may be awakening judging by seismic unrest. Seismicity in the area is characterized by data from permanent regional seismic stations and campaign local stations, as well as by data of the Kamchatka earthquake catalog. Seismic activity having nucleated at shallow depths in the vicinities of the Udina volcanoes since October 2017 may reflect a beginning cycle of volcanism. The earthquakes are mainly long-period (LP) 0.5-5 Hz events, which are commonly attributed to the movement of viscous magma and resonance phenomena in magma conduits. Such earthquakes may be a response to inputs of new magma batches to the plumbing system that feeds the volcanoes and thus may be precursors of volcanic unrest. Seismic campaigns of May-July 2018 near the Udina complex provided more rigorous constraints on earthquake coordinates and origin depths and showed that most of the earthquakes originated within 5 km beneath the Bolshaya Udina Volcano. Seismic tomographic inversion using the LOTOS code revealed a zone of high P -wave velocities, low S -wave velocities, and a high vP / vS ratio directly beneath the volcano. Such a combination of parameters typically occurs in active volcanic areas and marks intrusion of partially molten magma and/or liquid fluids. The velocity anomaly detected in 2018 is shallower than that recovered in 2014-2015. The seismic evidence, along with the available geological and geophysical data, record the movement of viscous magma related to the Udina feeding system in the middle crust, which is implicit proof for connection between the intermediate crustal and deep mantle magma sources renewed after a long lull.
																								



7.
THE RELATIONSHIP BETWEEN POWERFUL GEODYNAMIC IMPACTS AND AN INCREASE IN THE MERCURY CONTENT OF THE WATER OF THE ANGARA RIVER SOURCE (Baikal Rift Zone)

A.V. Klyuchevskii1, V.I. Grebenshchikova2, M.I. Kuz'min2, V.M. Demyanovich1, A.A. Klyuchevskaya1
1Institute of the Earths Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
2A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Mercury content in water, geodynamic impacts, strong earthquakes, seismicity, Lake Baikal, Angara River source

Abstract >>
The results of Hg content determination in the water of the Angara River source are considered in relationship with the seismic processes proceeding at different levels of the lithosphere in the Baikal Rift Zone (BRZ), the geodynamic rejuvenation of the South Baikal rifting attractor structure (RAS), and the time distribution of M ≥ 7 earthquakes which occurred at a significant distance from the water sampling station. The correlation coefficients calculated between the pairs Hg content-earthquake numbers n and Hg-logarithm of summary seismic energy lgΣ E S are most often low, thus indicating the absence of a statistically meaningful relationship between the remote seismic process and the dynamics of mercury release. However, the correlation coefficients in the vicinity of the Angara River source are high, thus proving the relationship of the mercury release with the deformation of this territory. The statistical validity of the «deformation-mercury release cause-and-effect relationship is verified by the fact that strong geodynamic impacts precede all meaningful Hg release maxima. In the period 1997-1998, the South Baikal RAS produced the highest impact, being in the phase of the maximum geodynamic activity. The combined impact of the RAS and the South Baikal earthquake of 1999 resulted in a series of the maximum mercury contents within 1999-2000. The subsequent gradual relaxation of the RAS activity led to a reduction in the average annual Hg content. Remote M ≥ 7 earthquakes and close strong earthquakes of the BRZ are responsible for the significant Hg release maxima. The predicted trend of the average annual Hg contents is their considerable increase in the fields of fluid discharge of faults under the powerful geodynamic impact of the RAS or strong earthquake. We assume that in the study lithosphere area, the powerful geodynamic impact caused an opening of fault zones leading to decompression with boiling and degassing of mercury and its rapid rise to the surface.
																								



8.
CORRECTION FOR GEOMAGNETIC SECULAR VARIATION EFFECTS: A NEW METHOD (case study of the Altai geodynamic network)

D.A. Kuleshov1, P.G. Dyadkov1,2, V.V. Plotkin1
1Trofimuk 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 1, Novosibirsk, 630090, Russia
Keywords: Geomagnetic field, secular variation, tectonomagnetism, Altai geodynamic network, interpolation fit

Abstract >>
The study focuses on detection of geomagnetic secular variation and the respective correction of tectonomagnetic data. A new technique is proposed for picking the secular variation component in the Earths main magnetic field recorded by precise measurements at 100 to 500 km sites on the surface. Long-period field variations presumably arise from fluid motions in the liquid core, at depths of about 3000 km, whereas the sizes of observation networks are within 500 km. The sources of secular variation, irrespective of their configuration, are much deeper than those of tectonomagnetic anomalies located above the Curie surface depths of ~10 to 20 km. Therefore, the surfaces that represent the space distribution of secular variation must be smoother than the respective surfaces for tectonomagnetic anomalies. The problem is thus to separate the regional and local signals from the two types of sources located at different depths. The new method is tested using data of yearly geomagnetic measurements at more than 30 repeat stations of a ~120 km long geodynamic network in Gorny Altai spanning the period from 2004 through 2018. The secular variation pattern is reconstructed by quadratic interpolation. The precise data corrected for secular variation of the main field reveal previously hidden tectonomagnetic anomalies up to 12 nT. The 3 nT positive anomaly falls within the zone of surface deformation caused by the Mw = 7.3 Chuya earthquake of 27 September 2003.