CRETACEOUS ENVIRONMENTAL CHANGES OF EAST RUSSIA

Abstract

The present paper summarizes the results of the investigations carried out in East Russia within the framework of the International Program of Geological Correlation (350) supported by UNESCO entitled "Cretaceous Environmental Change in East and South Asia" (1993-1998). Multidisciplinary studies made by paleontologists, biostratigraphers, sedimentologists, paleovolcanologists, and tectonists permitted the determination of synchroneity and interrelation of different geological and biological events, and re-establishment of the succession of Cretaceous climatic, biological, and physical-geographical changes in East Russia. In the conditions of an active continental margin permanently existing during the Cretaceous, and being displaced eastward, three major events, which affected essentially environmental and biotic changes, have been distinguished. The principal events occurred in the Hauterivian, when due to the plate reorganization and oblique subduction, a regime of transform margin was dominant, a transregional regression occurred, and the first Angiospermae appeared. The second tectonic reorganization occurred in the mid-Albian resulting in the formation of a giant East-Asian volcanic belt, which formed a longitudinal zonality against the background of the latitudinal zonality. A total cooling and considerable biota rejuvenation were caused by this event. The third considerable reorganization occurred in the mid-Maastrichtian that was characterized by the elevation of the continental margin, fall in temperature, and a cardinal reorganization of ecosystems with the extinction of numerous flora and fauna, including dinosaurs.