PALEOMAGNETISM OF THE VOROGOVKA GROUP (YENISEI RIDGE): TOWARDS THE SUBSTANTIATION OF THE VENDIAN GEOMAGNETIC PHENOMENON
E.V. Vinogradov1,2, D.V. Metelkin1,2, E.F. Letnikova3, L.R. Kosareva4, V.V. Abashev2,1, I.A. Vishnevskaya5
1Novosibirsk State University, Novosibirsk, Russia
2Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences,Novosibirsk, Russia
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
4Kazan (Volga Region) Federal University, Institute of Geology and Petroleum Technologies, Kazan, Russia
5 Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia
Keywords: Ediacaran, Yenisei Ridge, Siberian Craton, detrital zircons, paleomagnetism, paleogeography, Vorogovka Group.
Abstract
The study presents new paleomagnetic data for the carbonate-terrigenous section of the Vorogovka Group at its type locality along the Vorogovka River in the northwestern Yenisei Ridge. The data is synthesized with existing information on the age of the rocks, including the authors determinations based on detrital zircons from sandstones and Sr-chemostratigraphy for carbonate rocks from all three stratigraphic units of the group: Severnaya Rechka, Mutnina, and Sukhaya Rechka formations. These findings definitively indicate a younger age for the formation of the strata, in the range of 580–535 million years, with a relatively rapid rate of sedimentation, contrary to previous estimates. The anomalous paleomagnetic record characteristic of the Vendian (Ediacaran) – Early Cambrian period and the proximity of the paleopoles established for Siberia suggests that the rocks formed over a narrower time interval, between 580 and 560 million years. It is shown that the paleomagnetic record of the Vorogovka Group contains, in addition to a viscous component, a metachronous magnetization, presumably of Cambrian age, and two coeval components of primary origin. The coexistence of these components in a single section does not correspond to the actualistic ideas about the prevailing axial dipole geometry of the Earth's magnetic field and this stand as subject of a long-standing debate. The analysis of the new data and its comparison with existing paleomagnetic records for Siberia provide new insights into the interpretation of the Vendian geomagnetic phenomenon within an original hypothesis. According to this model, the appearance of a second magnetization component in the Vendian-Early Cambrian sections is explained by a sharp decline in the main dipole component of the geomagnetic field to values comparable to intensity of global magnetic anomalies. This phenomenon distorts the conventional paleomagnetic record to varying degrees, and during periods of ultra-low dipole strength, it can entirely replace the usual record. Accordingly, paleomagnetic vectors would no longer be oriented toward the magnetic pole but instead align with the nearest magnetic anomaly. This hypothesis is used to interpret not only the paleomagnetic directions observed in the Vorogovka Group but also the entire set of paleomagnetic data for the Vendian-Early Cambrian of Siberia.
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