A.M. Fetisova a,b,c*, R.V. Veselovskiy a,b**, M.P. Arefiev d,c***
aLomonosov Moscow State University, Moscow, 119991 Russia
bSchmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, 123242 Russia
cKazan Federal University, Kazan, 420008 Russia
dGeological Institute, Russian Academy of Sciences, Moscow, 119017 Russia
E-mail: *anna-fetis@yandex.ru, **roman.veselovskiy@ya.ru, ***mihail-3000@inbox.ru
Received April 20, 2020
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DOI: 10.26907/2542-064X.2020.2.228-243
For citation: Fetisova A.M., Veselovskiy R.V., Arefiev M.P. New paleomagnetic data on the Permian-Triassic sedimentary sections of the Moscow syneclise. Uchenye Zapiski Kazanskogo Universiteta. Seriya Estestvennye Nauki, 2020, vol. 162, no. 2, pp. 228–243. doi: 10.26907/2542-064X.2020.2.228-243. (In Russian)
Abstract
The results of a detailed paleomagnetic study of the following five Permian-Triassic sections of the Russian Platform were discussed: Slukino (Vladimir region), Sartakovo and Prudovka (Nizhny Novgorod region), Klykovo and Gavrino (Vologda region). The study is important and intriguing due to the current lack of any representative and reliable paleomagnetic data on the Permian-Triassic age for Eurasia. These data can be helpful for testing the hypothesis about the possibility of relative movements of Eurasia’s lithospheric blocks in the post-Paleozoic time, as well as about the geocentric axial dipole in the Paleozoic and Mesozoic. In order to obtain new paleomagnetic poles, samples from five most promising and well-dated cross-sections of the Permian-Triassic red beds located on the eastern slope of the Moscow syneclise were taken. Laboratory treatment was carried out with the use of modern equipment and advanced techniques. Stepwise thermal demagnetization showed the presence of a paleomagnetic record of excellent quality in all the studied sections, thereby making it possible to obtain new paleomagnetic data of high accuracy and reliability. The resulting paleomagnetic poles demonstrate a so-called “far-side effect”, i.e., they are shifted relatively to the expected position of the mean Permian-Triassic paleomagnetic pole of the East European Platform along the paleomeridian towards the opposite side of the sampling site. Presumably, the reasons are (a) an inclination shallowing in the studied sedimentary rocks, (b) the presence of a significant contribution of non-dipole components to the main geomagnetic field about 250 million years ago, (c) local tectonics. The results of this study can be of considerable interest for clarifying the paleogeographic position of the East European Platform and testing the hypothesis of tectonic rigidity of Eurasia. Furthermore, they are an imporant factual material for analyzing the key features of the geomagnetic field at the Paleozoic-Mesozoic boundary.
Keywords: Permian, Triassic, paleomagnetism, red beds, Moscow syneclise, East European Platform
Acknowledgements. Paleomagnetic studies were supported by the Russian Foundation for Basic Research (project no. 18-05-00593) and, in part, by the Government of the Russian Federation (project no. 14.Z50.31.0017), as well as by the R&D project performed within the framework of the state assignment to the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences and to the Department of Geology of the Moscow State University and by the subsidy allocated to the Kazan Federal University for the state assignment no. 671-2020-0049 in the sphere of scientific activities. Sedimentological investigations were performed as part of the state assignment no. 0135-2019-0073 to the Geological Institute of the Russian Academy of Sciences.
Figure Captions
Fig. 1. Location of the studied sections (shown as stars) on the tectonic map of Eastern Europe (according to [19] with simplification).
Fig. 2. Magnetic susceptibility anisotropy (MSA) of rock material from the studied sections. Leftwards: stereogram showing the distribution of long, intermediate, and short semi-axes of the MSA oval (K1, K2, and K3, respectively) in the projection on the lower hemisphere. Top right: Jelinek diagram [20] illustrating the dependence of MSA ellipsoid shape (T) – flattened/elongated – on anisotropy degree (P). Bottom right: dependence of the MSA degree on magnetic susceptibility (Km).
Fig. 3. Directions of the characteristic magnetization components for the studied outcrops at the level of samples and their mean values with the confidence level of 95%.
Fig. 4. Comparison of the obtained paleomagnetic poles with the curve of apparent migration of the paleomagnetic pole of the East European Platform [16].
Fig. 5. Results of the thermal magnetic cleaning of the samples of rocks typical in the studied sections: stereograms, Zijderveld diagrams, and NRM demagnetization curves. Black and white circles on the stereograms indicate the projection of the vector on the upper and lower hemispheres, respectively; black and white circles on the Zijderveld diagrams show the projections of the vector on the horizontal and vertical planes, respectively.
Fig. 6. Range of the virtual geomagnetic poles (Sb) for the studied outcrops as compared with the model curve of secular variations over the last 5 million years [13]. See main text for explanation.
References
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