The Eocene Fossil Plants, Spores, Pollen, and Dinocysts from the Tavda Formation, the Pavlodar Area near the Irtysh River

摘要

The Bartonian Age of subtropical small-leaved fossil flora from green clay members of the Tavda Formation, the Pavlodar area near Irtysh River, is substantiated for the first time based on dinocysts detected in outcrops of the Irtysh–Karaganda Channel. The microplankton composition suggests that the lower Tavda Subformation was deposited during the first transgressive phase of the late Eocene. A sea basin that spread at that time over southern and central regions of West Siberia was connected with the Tethys and reached the northern marginal areas of the Kazakh Hills. The Castanopsis pollen is dominant in palynological assemblage and occurs in association with fine pollen of the Quercus gracilis–Q. graciliformis group. The assemblage is likely indicative of the earliest phase of climatic inversion, when the Lutetian monsoon climate in middle latitudes of western Asia turned into seasonal climate of the Mediterranean type with hot summers and most intense precipitations during the winter period.