Evolution of Albian-Cenomanian floras of Northeast USSR and the association between their composition and facies conditions

Abstract

We consider the evolution of Albian-Cenomanian floras of the Northeast USSR for both coal-bearing and "non-coal" deposits, taking the evolution of paleofloras in single-facies (coal-bearing) deposits as a base. In general, the taphofloras have been assigned to the sequence from which the plant remains were collected. During Albian-Cenomanian time the angiosperms migrated from higher to lower levels. The observed decrease in the role of angiosperms during Cenomanian (Arkagala) time after their "expansion" during Albian time (in the Toptan and Arman suites) is explained by their establishment at different topographic levels. We show parallel increase in the role of conifers and angiosperms in the floras from the coal-bearing deposits from the Albian to the Cenomanian. A temperature minimum occurred during Arkagala time. It is likely that old, pre-Albian angiosperms may be found in sediments of the intermontane basins. In analyzing the level of evolution of the floras on the Early - Late Cretaceous boundary, especially the angiosperms, one must take into account the facies in which they are present. —Authors.