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Russian Geology and Geophysics

2021 year, number 7

1.
THE CONTINENTAL CRUST BENEATH THE WESTERN AMERASIA BASIN: MECHANISMS OF CRUSTAL SUBSIDENCE

E.V. Artyushkov1, O.E. Smirnov2, P.A. Chekhovich1,3
1Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
2FSBI “VNIIOkeangeologiya”, St. Petersburg, Russia
3Lomonosov Moscow State University, Moscow, Russia
Keywords: Ultradeep basins, gravity anomalies, isostatic equilibrium, CDP seismic reflection survey, crustal stretching, eclogitization, Moho, Amerasian Basin, Podvodnikov Basin

Abstract >>
The western part of the wide Amerasian Basin in the Arctic Ocean includes two small basins: the Podvodnikov and the Makarov ones. Analysis of the data on the sedimentary-cover structure and the crustal-subsidence history suggests that despite the large depth of water (3-4 km), both basins are underlain by continental crust. Before the rapid formation of deep-water basins in the early Miocene, the crustal surface was close to the sea level for a long time. Lithospheric stretching made only a minor input to the crustal subsidence. The main cause of the subsidence was prograde metamorphism in the lower continental crust with the transformation of gabbroids into denser eclogite-type rocks. The P -wave velocities in eclogites and mantle peridotites are rather similar. Therefore, when interpreting the seismic data, high-velocity eclogites are commonly considered as the uppermost part of the mantle located below the Moho, while the overlying rocks are shown as attenuated continental crust in the Podvodnikov Basin and as oceanic crust in the Makarov Basin. The proposed mechanism makes it possible to modify the model of crustal structure and to interpret high-velocity eclogites as the lower part of the continental crust that has undergone prograde metamorphism under the impact of mantle fluids.



2.
THE DEPTH TO MAGNETIC SOURCES IN THE ARCTIC AND ITS RELATIONSHIP WITH SOME PARAMETERS OF THE LITHOSPHERE

A.I. Seredkina, S.V. Filippov
Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation, Troitsk, Russia
Keywords: Magnetic sources, geomagnetic anomalies, EMAG2v3 model, WDMAM 2.0 model, Fourier spectrum, lithosphere, Arctic

Abstract >>
The depth to magnetic sources in twenty Arctic tectonic provinces is determined from azimuthally averaged Fourier power spectra of geomagnetic anomalies according to the EMAG2v3 and WDMAM 2.0 global models. The resulting depths to the centroid and bottom of the magnetic lithosphere are more reliable than the depth to the upper magnetic boundary. The depth to the bottom of magnetic sources, corresponding to the Curie point depth, varies from 25.3 to 38.1 km in different provinces. The Curie point depth estimates are correlated with several parameters of the lithosphere. They are directly proportional to the lithospheric thickness and inversely proportional to average upper mantle temperatures, but the relationship with the intensity of long-wavelength satellite magnetic anomalies and crustal thickness is poor. The magnetic sources are located at crustal depths in most of the provinces, but the upper mantle may be magnetic beneath deep-water oceanic basins and the Laptev Sea. The results for the Laptev Sea shelf support a passive mechanism of current lithospheric extension in the area.



3.
MIDDLE-UPPER CAMBRIAN TRILOBITES OF THE GENUS NGANASANELLA ROSOVA, 1963 AND THEIR STRATIGRAPHIC SIGNIFICANCE

A.L. Makarova
All-Russian Research Geological Oil Institute (Novosibirsk Department), Novosibirsk, Russia
Keywords: Trilobites, biostratigraphy, upper Cambrian, Orakta Formation, Siberian Platform, Kulyumbe River

Abstract >>
This paper presents a revision for the genus Nganasanella Rosova, 1963, first described in the stratotype of the Kulyumbean Regional Stage of the Kulyumbe River section (northwest of the Siberian platform). This section is typical for the upper Cambrian sediments of the Kotuy-Igarka facies region, formed in a shallow marine shelf. As shown by the study, the genus comprises seven species. The species N. nganasanensis Rosova, 1963 (type species), N. tavgaensis Rosova, 1963, N. glabella (Kobayashi), 1943, N. granulosa Rosova et Makarova, 2009, and N. vernacula Rosova et Makarova, 2009 are found in the Siberian Platform. The species N. australica sp. nov. occurs in northeastern Australia. The species N. trisulcatus (Ergaliev), 1980 is widespread in southern Kazakhstan. Some species ( N. granulosa and N. vernacula ) are found in open marine facies sediments along with the cosmopolitan agnostid species Glyptagnostus reticulatus (Angelin), 1851, serving as a marker of the lower boundary of upper Cambrian strata in the International Chronostratigraphic Chart and the General Stratigraphic Chart of Russia. The species N. trisulcatus and N. australica are found slightly above Glyptagnostus reticulatus . Representatives of the genus Nganasanella are a link between strata of different facies containing different trilobite associations. Their stratigraphic position can serve as an argument for the correlation of the Kulyumbean Regional Stage with units containing Glyptagnostus reticulatus , i.e., the Omnian and Idamean regional stages, the lower parts of the Kutugunian Horizon and the Sakian Regional Stage, and the Paibian Stage of the International Chronostratigraphic Chart.



4.
PALYNOSTRATIGRAPHY AND PALEOENVIRONMENTS IN THE GORODISHCHI SECTION (Middle Volga River region, Kimmeridgian-Hauterivian)

E.B. Pestchevitskaya
Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
Keywords: Dinocysts, spores and pollen, Kimmeridgian-Hauterivian, biostratigraphy, correlation, paleoenvironments, European Russia

Abstract >>
Eight dinocyst-based and three spore- and pollen-based biostratigraphic units are defined in the Kimmeridgian, Volgian, and Hauterivian of the Gorodishchi section, based on a biostratigraphic analysis of the successions of marine and terrestrial palynomorphs. Algological assemblages are described in more detail, and additional criteria for the definition of dinocyst zones established by previous researches are given. A more detailed biostratigraphic subdivision of the middle part of the Volgian is proposed. A local dinocyst zone in the Hauterivian and a biostratigraphic succession of spore-pollen units in the entire section are described for the first time. The research results demonstrate that the boundaries of many palynostratigraphic units exhibit a considerable correlation potential. Based on a biofacies analysis of the microphytoplankton, the dynamics of transgressive-regressive events is studied in relation to the accompanying oxygen and trophic conditions. Possible relationships between marine paleoenvironments and climatic changes reconstructed on the basis of spore-pollen data are discussed.



5.
SEISMOGRAVIMETRIC METHODOLOGY: SPECIFICS AND APPLICABILITY TO THE SIBERIAN PLATFORM

V.A. Kochnev
Institute of Computational Modeling, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia
Keywords: Seismogravimetric method, upper section, density-velocity relation, static corrections, time and depth sections

Abstract >>
The paper presents a new seismogravimetric method for estimating static corrections used in processing of seismic data and in construction of time and depth sections. The method efficiency is demonstrated by comparison of the results of industrial and new experimental processing of data for the western slope of the Nepa-Botuobiya anteclise.



6.
STUDY OF GEOSTATISTICAL INVERSION IN THE LITHOLOGIC DISTRIBUTION AND VELOCITY MODELING OF THICK IGNEOUS ROCK IN THE FY AREA, NORTHERN TARIM BASIN, CHINA

Y. Xu, H. Yang, G. Peng, X. Deng, Q. Miao, Y. Ma, J. Liu
1School of Resources and Geosciences, China University of Mining and Technology, Xuzhou, China
2Institute of China Petroleum Tarim Oilfield Company, Korla, China
3School of Nuclear Science and Technology, Lanzhou University, Lanzhou, China
Keywords: thick igneous rocks, geostatistical inversion, lithology distribution, velocity modeling

Abstract >>
In the northern Tarim Basin, a large number of thick igneous rocks are encountered in the drilling process in the Permian. Their lithology and velocity are very strongly, which has a great influence on migration imaging of the “beaded” areas. It is very important to conduct the fine lithology identification and high-precision velocity modeling of the igneous rocks for the exploration and development of the reservoirs. A geostatistical inversion method to obtain the igneous-rock lithologic distribution pattern and velocity modeling in the FY area of the northern Tarim Basin is introduced in this paper. The results show that the application of the geostatistical inversion method greatly improves the resolution of lithology identification. This helps us further understand the Permian igneous rocks distribution in the FY area. Comparison between the seismic facies classification maps of the FY study area shows that the obtained velocity model can reflect the lateral distribution of igneous rocks well. At the same time, the velocity model can reflect the variation of igneous rocks velocity in detail and has a high precision. The average velocity error of the wells participating in the inversion is less than 2%, and the minimum average velocity error is 0.23%. Finally, the velocity model is applied to seismic data processing, and the processing results indicate that it can help to improve seismic migration imaging. The study demonstrates that the geostatistical inversion method can provide a high-precision velocity model for formation pressure prediction and seismic data processing and interpretation, ultimately guiding the exploration and development of oil.



7.
FAULT MESH PETROLEUM PLAYS IN THE DONGHETANG AREA, TABEI UPLIFT, TARIM BASIN, NW CHINA, AND THEIR SIGNIFICANCE

Q. Liu, H. Xu, Z. Lei, Z. Li, Y. Xiong, S. Li, B. Luo, D. Chen
1Department of Geoscience, China University of Petroleum, Beijing, China
2Institution of Petroleum Exploration and Development of SW Tarim Basin, Tarim Oilfield Company, PetroChina, Korla, China
3Jiangxi Engineering Laboratory on Radioactive Geoscience and Big Data Technology, East China University of Technology, Nanchang, China
4Jiangxi Engineering Technology Research Center of Nuclear Geoscience Data Science and System, East China University of Technology, Nanchang, China
5Research Institution of Petroleum Exploration and Development, Zhongyuan Oilfield Company, Sinopec, Puyang, China
Keywords: Allogenic and far source accumulation, fault mesh petroleum plays, multiple accumulation and adjustment, Tabei Uplift, Tarim Basin, NW China

Abstract >>
The hydrocarbon formation mechanism and potential targets in clastic strata from the Tabei Uplift, Tarim Basin, are documented using the fault mesh petroleum plays theory, based on integrating seismic, well log, well core and geochemistry data. The reservoirs in the Donghetang area are typical allochthonous and far source fault mesh petroleum plays. There are two sets of fault meshes in the study area: (1) the Donghe sandstone and combination of Permian and Triassic strata and (2) combination of the JIV and JIII formations in the Jurassic strata. The fault mesh petroleum play in the Jurassic is a secondary reservoir that originates from the Carboniferous Donghe sandstone reservoir adjustment based on source correlation. The fault mesh carrier systems are divided into four styles according to the fault mesh architecture: (1) fully connected, (2) fault-unconformity-transient storage relay, (3) fault-transient storage-unconformity relay, and (4) transient storage-fault relay. According to the characteristics of the fault mesh petroleum plays, the reservoirs are of 15 types and form three categories: upper transient storage, inner transient storage, and margin-transient storage. Integrated analysis of the hydrocarbon generation and faulting time periods reveals that there were four periods of hydrocarbon charging, with the first three stages charging the reservoirs with oil and the last stage charging the reservoirs with gas. There are multiple stages of reservoir accumulation and adjustment in the fault mesh in the study area. These multiple stages of fault mesh accumulation and adjustment are the main reason that the multiple vertical units of the reservoirs have different hydrocarbon properties. Fault-block reservoirs and lithologic reservoirs related to the inner transient storage and upper transient storage styles are the main exploration targets in the clastic strata in the study area.