Early Cretaceous spore and pollen assemblage from the Yixian Formation in the Qianjiadian Depression of Kailu Basin and its paleoclimate evolution

The study of plant succession and climate change in Cretaceous is of great significance for the understanding of formation and evolution of the present ecological environment. The study on the palynology from the Yixian Formation can provide palynology data and lay the basis on Early Cretaceous stratigraphic classification and correlation in the northeastern area of Kailu basin. Based on the analysis of sporo-pollen fossils of 47 species from 39 genera recognized from the bottom of well QIV-65-136 in the Qianjiadian depression, Kailu Basin, the Cyathidites-Pinuspollenites-Protoconiferus assemblage was established. According to the age range of typical species, content change on key species and horizontal contrast, this assemblage should be dated as the early Early Creataceous, the horizon is equivalent to the Yixian Formation. The palynoflora shows the Coniferales plants on the high elevation mountain around the lake, accompanied by Podocarpaceae, Taxodiaceae, Cycadaceae, Araucariaceae and Cheirolepidiaceae plants, the fern such as Osmundaceae, Cyatheaceae, Schizaeaceae plants growing under the trees near the lake. Vegetation is occupied by coniferous, representing a humid temperate to subtropical zone.