| Cretaceous is a particular period in geological history,it is considered to be a typical of the "greenhouse climate".But there have not been enough evidences from land sendiment for this viewpoint.,Sichuan Basin is one of the most representative in the Cretaceous in china , and the area of Ya'an in Sichuan Basin is relatively complete region with formation and development of the Cretaceous, in which a group of red classic deposited with gypsum.In order to better understand the current climate system and predict the future climate, we need to know how the past climate was changing . Information from ancient climate, ancient environment of the Cretaceous will be an important aspect of Cretaceous study in the new times.So research into climate change of Cretaceous is especially important.In this paper, on the basis of study of area geologic background, the measured three stratigraphic sections of Cretaceous have been described in detail. Stratigraphy of Cretaceous was divided into three formal lithostratigraphic units which are Tianma shan Formation,Jiagua Formation and Guankou Formation according to the principles of lithostratigraphic division ,and it is the first time for Jiaguan Formation (K1j)to be subdivided into two lithologic members and Guankou Formation (K2g) to be subdivid -ed into three lithologic members. The lithologic characteristics,stratigraphic thickn -ess and contact relations of each formation and each member have been ascertained.On the basis of analysis and identification of fossils samples ,according to assem -belage and stratigraphic distribution of fossils Schizaeoisporites-Cicatricosisporites- Classopollis-Lygodiumsporites spore and pollen Assembelage Zone has been establi -shed in Jiagua Formation for the first time and also Limnocythere helmifer- Candona extenua te-Cypridea ostracods Assembelage Zone and Schizaeoisporites-Classopollis -Ephedripites pollen Assemblage Zones have been established in Guankou Formation, then the geological age of each Assemblage Zones was discussed. It is asserted that Tianmashan Formation and Jiaguan Formation belong to the Lower Cretaceous, and Guankou Formation belongs to the Upper Cretaceous according to fossil Assembelage Zones and regional Stratigraphic comparison.Sedimentary environments of Cretaceous stratigraphy in Ya'an region are. analys -ed The sedimentary environments of Tianmashan Formation and Jiaguan Formation in studied area are mostly composed of braided rivers to meandering river,and Guan -kou Formation is mostly composed of lake,sub-facies and microfacies are also analys -ed in detail. It is concluded that Sedimentary environment evolution was from river to Delta lakes and then to lakes and salt lakes in arid climate.Paleoclimatic evolution of the Cretaceous period in the studied area is discussed based on information of rock and minerale,pollen and the geochemistry data.Detrital component of Sandstone shows that Jiaguan period is mainly semi-dry climate and there were two times short-term extreme drought in the Early Cretaceous and one drought in early Late Cretaceous. Through spore and pollen vegetation paleoclimate studies , it is recognized that Jiaguan period of the Early Cretaceous is tropical, tropical to sub-tropical semi-dry climate and Guankou period of the Late Cretaceous is tropical to subtropical arid climate. Study of geochemistry of main and rare elements and their ratios shows that Tianmashan period is hot and dry climate with lower rainfall in the Early Cretaceous. Jiaguan period is relatively warm climate with relatively more abundant rainfall;Guankou period is hot and dry climate and oxidation is weak. In addition, the ratios of CaO / MgO and SiO2/A12O3 also indicate that in the early Late Cretaceous one extreme hot and droughty weather events had occurred. then it becomed to the relatively warm climate, but overall the paleoclimatic was heat or droughty. This conclusion accords with the results of detrital component of sandstone and pollen analysis .
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