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The Permian System in the U.S.S.R.
The present state of Permian stratigraphy in the Soviet Union is discussed on the basis of analysis of modern data. The base of the Schwagerina beds and their equivalents is adopted as the lower boundary of the Permian System, while the upper boundary is believed to lie at the base of the Otoceras Zone and its stratigraphic equivalents. The geocratic character of the Permian Period creates special difficulties for the development of a general stratigraphic scale for this System. Therefore subdivision of the Permian into stages, which is now adopted in the Soviet Union, needs some improvement. It is expedient, however, to retain the present subdivision of the Lower Series into three stages as follows: Asselian, Sakmarian and Artinskian. It seems most acceptable to subdivide the Upper Permian also into three stages which correspond to three distinctly pronounced phases of marine faunal development. The following are therefore proposed, In ascending order: Svalbardian (Paykhoyan), Kazanian and Dzhulfian.
The main feature of the marine and terrestrial faunal development during the Permian is the gradual extinction of many Paleozoic groups. The rate of this process was different for separate types and classes of animals. Moreover, the same groups in different areas did not become extinct simultaneously. With the extinction of Paleozoic taxa the rise of separate Mesozoic groups was taking place during the Permian. Some, such as the Ceratites, for instance, had already appeared in the Early Permian.
The development of a terrestrial flora during the Permian also occurred gradually. Again the change from paleophytic flora to mesophytic in different areas was not simultaneous. There is thus no evidence of sudden or catastrophic changes in development of fauna and flora in the latest Permian and near the boundary with the Triassic. It is possible to state only that during the Permian Period many organic groups were undergoing a critical phase of development. Extinction of ancient Paleozoic elements during the Permian was greater than the rise of new Mesozoic ones.
The prevalent type of interrelationship between the Upper Permian and Lower Triassic beds is one of unconformity, accompanied by erosion or nondeposition of a more or less significant portion of Upper Permian rocks. An especially widespread type of Permian-Triassic contact is the paraconformity (nonsequence). Reliable data establishing the existence of a gradual but continuous transition between Permian and Triassic rocks are much more rare, however.
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