CORRELATIVE REFERENCE LEVELS OF THE PERMIAN

Abstract

The analysis of Permian biotic and abiotic events has revealed a series of contrasting global biostratigraphic levels, to which significant changes in faunal assemblages are confined. The most important among them - the "Kungurian," Kubergandian (Roadian) and Djulfian stages - are related to transgressions, the Kungurian being also associated with a large-scale paleogeographic reorganization. The global character of these transgressions and related biotic changes are caused most likely by eustatic sea level fluctuations. The most significant changes in the Permian biota, which showed up differently in basins of the Boreal and Tethyan realms, occurred in the early "Kungurian" time. The Kubergandian (Roadian) Stage is associated with a wide geographic distribution of the Roadian ammonoid assemblage, which includes the Ceratitida order, and the simultaneous appearance of Mesogondolella nankingensis. The Djulfian Stage is characterized by the extinction of almost all higher fusulinids, the mass development of aberrant genera, the appearance of araxoceratids, and substantial changes in the evolution of corals, brachiopods and other faunal assemblages. Levels of a lower order are also established. One of them corresponds to the maximum development of the mid-Permian transgression (the Neoschwagerina craticilifera-Afghanella schencki Zone in, the Tethys and its analogues in other areas) and marks the appearance of the Wordian ammonoid assemblage. The mid-Midian level coincides in time with the boundary of the Kaiama and Illawarra paleomagnetic hyperzones and is marked by the appearance of the Capitanian zonal genus Timorites. The stages revealed here represent reference levels, which allow wide correlations to be made.