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Problems of Upper Permian and Triassic Stratigraphy on the Russian Platform, in the Light of Paleomagnetic, Paleontological and Lithostratigraphic Evidence
Stratigraphic studies of reference sections of Upper Permian and Triassic red beds on the Russian Platform have led to the compilation of a detailed stratigraphic succession. At the same time paleontological work has revealed a vertical distribution of terrestrial vertebrate assemblages which closely corresponds with stages and substages and therefore has some biostratigraphic value.
Detailed paleomagnetic studies of the Permian and Triassic red beds of the platform have indicated the presence of alternating normal and reversed magnetic episodes from which a standard paleomagnetic section has been compiled. This section may conveniently be correlated with the major subdivisions of the stratigraphic succession.
Continental deposits of the Kazanian Stage are characterized by the Cis-Ural Deinocephalus assemblage, while the Lower Tatarian Substage is typified by the Isheev Deinocephalus assemblage. Paleomagnetic work reveals that the deposits of the Ufimian and Kazanian Stages, and the Lower Tatarian Sub-stage, collectively represent a single, continuous paleomagnetic unit of reversed polarity (R1P).
The Upper Tatarian Substage is characterized by the Severodvinsk Pareiasaurus and the Gorki Batrachosaurus assemblages. Paleomagnetically, this substage is divided into four units: N1P, R1P, N2P and R2P. The unit R2P is not present in the Kazan region and in the sections exposed in the southern Urals.
In the overlying Triassic deposits, the Lower Triassic section can be divided into four subdivisions based on alternations in paleomagnetic direction: N1T, R1T, N2T, and R2T. The Middle and Upper Triassic strata have normal magnetic fields and can provisionally be regarded as a single zone N3T (the Cis-Ural zone).
Permian and Triassic deposits of the Russian Platform have long been considered a standard for correlation with synchronous rocks of other regions of the world. The relative distribution of normal and reversed magnetism in Permian and Triassic rocks on the platform is essentially the same as in North America, South Africa and Australia, thus demonstrating the objective value of paleomagnetic correlations. Boundaries of major zones, such as the R-Kiama-NR-Illawara zone and the NR-Illawara-N-Cis-Ural zone can therefore be regarded as reliable isochronous units of worldwide significance.
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