LATE PERMIAN LIMESTONES AND THE PERMIAN-TRIASSIC BOUNDARY: NEW BIOSTRATIGRAPHIC, PALAEOBIOGEOGRAPHICAL AND GEOCHEMICAL DATA IN CAUCASUS AND EASTERN EUROPE

Abstract

This paper presents biostratigraphical and palaeogeographical correlations, in a post-Hercynian and pre-Cimmerian tectonic framework, between stratigraphic sections of Late Permian age in two important and remote areas, with some considerations concerning neighbouring countries. It concerns mainly the Nikitin sequence (Kuban, Russia) and the BUk Mountains (Hungary), and describes the carbonate environments, microfauna diversity, foraminiferal assemblages, calcisponge and brachiopod constructions, and gymnocodiacean accumulations. This study is extended to former Transcaucasia (southern Armenia, Georgia and Adzerbadjan), the Alborz Belt in northern Iran, Italy and the Carnic Alps. It emphasizes a relatively simple biosedimentary evolution, which permits a confident palaeogeographic reconstruction. New geochernical results provided some additional markers, in particular small microspherules consisting of Cr/Ni spinels of cosmic origin. They occur in several sections in a defined position at the Permian-Triassic boundary based on biostratigraphic correlations (conodonts, foraminifers, last Permian reefal phenomena). These geochernical data might be related to a possible meteorite impact, Nevertheless, another global alternative phenomenon occurs. From the Latest Permian to the Earliest Triassic, the carbonate production or biomineralization is preferentially concentrated in the confined, intertidal or lagunal zones, and its evolution is relatively progressive from gymnocodiacean accumulations of the Latest Permian to the microbialites of the Earliest Triassic.