The Early Cretaceous Palynoflora Of The Liupanshan Group And Bayingebi Formation, And Its Paleoclimatic And Paleogeographic Implications, Central China

The Cretaceous is a period of the warmest Greenhouse state in the geologic history. To understand the formation of global warming and evolution, it is important to study the climate change and geographical division. This paper investigates the climate evolution and division in the mainland during the Early Cretaceous, based on the palynologic data of the Lower Cretaceous of Liupanshan basin and Yin-Ejinaqi Basin together with regional palynologic data.Similar Early Cretaceous pollen assemblages are found both in the Liupanshan Basin and Yin-Ejinaqi Basin, which are dominated by Classopollis-Schizaeoisporites-Cicatricosisporites. The Cheirolepidiaceae takes the absolutely advantage position and conifers secondary, there are some xerophytic shrub of Schizaeaceae and Ephedraceae, while Ferns takes relatively few proportion. Comparatively, the pollen assemblages of Liupanshan Basin are richer, which are charactered by abundant Cheirolepidiaceae pollen. Whereas, the coniferous pollen is relatively higher in Yin-Ejinaqi Basin. The two pollen assemblages all indicate a dry and hot climate condition.The age of Liwaxia-Naijiahe Formation of Liupanshan Group is Aptian-Albian indicated by the preservation of Cicatricosisporites, Schizaeoisporites, Tricopopollenites, wulongspor, reticulate, Hsuisporites, Appenaicisporites and Yichangsporites tricyclosus and so on. The age of Bayingebi Formation is correlated to Late Barremin to the Middle Albain because of the abundance of Cicatricosisporites, Densosisporites, Schizaeoisporites as well as Foveotriletes in the pollen assembledge.The content of Cheirolepidiaceae, Schizaeaceae Ephedraceae, conifer and ferns in the pollen assemblage of Huoshizhai section can be divided into five zones, exhibiting a hot and dry-warm and dry-hot and humid climate change trends, which are in accord with the variation of the global sea surface temperature. The pollen assemblages of Bayingebi Formation can be divided into three association zones, the trends is from warm and humid to hot and dry and present a quickly changed climate feature. The paleogeography of the North China can be divided into five areas during late Early Cretaceous in terms of pollen data, in particular, the content of Classopollis and Disacciatrileti, in the huge basin in the northern China:1) Northeast warm and humid monsoon region (NEM), showing a cool and humid environment,with a typical monsoon climate of medium latitudes; 2) Eastern coast monsoon zone (EM), warm and dry season; 3) The dry and warm hinterland of china (CD); 4) Mediterranean climate of Tethys coast(TD), which is probably controlled by the paleo-Mediterranean climate due to the Subtropical High over the Tethys sea in winter, and migrate to north coast of Tethys in summer; and 5) The transition region (TR)(between CD and TD). In contrast, the Southern china is tropical and dry area, which was subject to Subtropical High existed all the year and induced the occurrence of extremely dry and warm climate in South china.