ALBIAN-LATE CRETACEOUS PHYTOSTRATIGRAPHY AND FLORAL EVOLUTION IN THE NORTH PACIFIC

Abstract

Different views on the composition and stratigraphic succession of the Cretaceous floras in northeastern Asia are considered. These floras populated different landscapes of that time and their correlation are difficult to correlate. In the Late Cretaceous time, northeastern Asia and Alaska were partly occupied by sea basins bordered by coastal plains with well developed river systems. In the inner land areas, there were uplands and plains, which escaped flooding. Continental deposits were accumulated there in isolated depressions. The upland of the Okhotsk-Chukchi volcanogenic belt extended along the eastern coast of the Asian continent. All late Albian-Late Cretaceous floras in coastal plains of northeastern Asia and Alaska were dominated by angiosperms. The intracontinental depressions and rises of the volcanogenic upland were occupied by the "Cenophytic" floras with prevailing angiosperms, which are correlatable with the coastal floras, and by the "Mesophytic" ones consisting of dominant ferns and gymnosperms associated with sporadic angiosperms. The coexistence of different floras can be explained by the ability of early angiosperms to occupy the disturbed vegetation-free habitats of the coastal plains, which permanently originated in response to sea transgressions and river meandering. These plant associations gradually penetrated along river valleys into the inner areas populated by coniferous-fern vegetation.