Early Cretaceous Palynoflora in Zhangye National Geopark and Its Palaeoenvironmental Significance

The Early cretaceous Hongshanwan formation is the main part of the colorful hilly landform of Zhangye National Geopark, but there lack some reliable studies on biostratigraphy, paleoecology and paleoenvironment for a long time. Based on the palynological fossils of 22 genera and 6 species newly discovered in Hongshanwan formation, the palynological flora in Hongshanwan area has been established in this paper. According to the flora characteristics, the paleoecology, paleoclimate, paleogeography and sedimentary environment of early cretaceous Hongshanwan formation has been further discussed. The results show that the Hongshanwan formation has dry climate and single vegetation in early stage, with sporopollen combination of Abietineaepollenites/Pinuspollenites. The late palynological assemblage is Cycadopites-Perinopollenites, with a large number of double balloon pollen, reflecting a warm and humid climate and obvious vertical zonation of plants. Based on the palynology model, six SEG types have been defined by taking the Hongshanwan as an example, such as highland, lowland, river, forerunner, coast and tide. And then, the terrestrial ecosystem around the lake basin has preliminarily constructed.