SOME UNSOLVED PROBLEMS OF TRIASSIC STRATIGRAPHY IN EASTERN EUROPE

Abstract

Two problems of the continental Triassic stratigraphy of East Europe are considered: (1) correlation between the Lower Triassic horizons of the Moscow syneclise and the northern Caspian region and (2) correlation of the Middle Triassic horizons of the southern Cis-Urals and northern Caspian region with subdivisions of the International Stratigraphic Scale. The interdepartmental meeting on Triassic stratigraphy of the northern Caspian region (1999, Saratov) decided to substitute the former Ershov and Baskunchak regional horizons by the Lower Triassic Vetluga and Yaren superhorizons of the Moscow syneclise, respectively. However, the unification, according to which the Yaren age is accepted for deposits with Baskunchak charophytes in the Moscow syneclise, is not substantiated by occurrence of associated terrestrial fossil vertebrates. There is evidence that the Yaren Superhorizon of the stratotype area may differ in range from the corresponding interval in Caspian sections, since the latter probably includes analogs of the upper Vetluga Superhorizon. The boundary position between two Middle Triassic units of the southern Cis-Urals, i.e., between the Donguz Horizon with the Eryosuchus fauna of tetrapods and the Bukobai Horizon with the "Mastodonsaurus" fauna (found also in the upper Inder Horizon of the Caspian region), remains controversial. According to micropaleontological data, it coincides with the Anisian-Ladinian boundary, being placed inside the upper Ladinian based on vertebrate faunas. The reasons responsible for controversial viewpoints may be as follows: (1) the Germanic and Alpine Triassic section used as a reference by dating the East European paleontological remains can be imprecisely correlated; (2) the vertebrate-based correlations are based on ornamentation on dermal bone of amphibians (plagiosaurs), the evolution rate of which could be different in Central and Eastern Europe); and (3) of microfauna and palynological records can be of insufficient resolution ability for the long-distance correlations.