PALYNOEVENTS SINCE LATE CENOZOIC IN WEIHE VALLEY AND CLIMATE CHANGES

Weihe valley is one of the areas where the study on late Cenozoic palynology began very early,involving more than twenty sections. By comparing the temporal and spatial distribution of the sporollon assemblages coupled with paleo-geomagnetism dating,we have ten areal zones. Since 3.5MaBP,the palynoflora were found to have evolved go through five stages,i.e.broad-leaf trees stage,conifer trees stage,woody grassland and grassland stage,woody grassland and desert grassland stage,grassland stage,and lastly woody grassland and grassland. These stages mark the megaevolution of the surface's environments beginning respectively from 2.5MaBP,2.0MaBP,1.4/1.6MaBP,and 0.8MaBP.