Magnetostratigraphic Chronology And The Material Source Of The Paleogene In The Wuwei Basin,the Northeastern Of The Tibet Plateau

The northeastern of the Tibet Plateau is the key to studying the uplift and environmental effects of the plateau in Cenozoic,there are a series of sedimentary basins which is important for studying the tectonic evolution of the basins and the uplift process of the Tibet Plateau.The Hexi Corridor basin has received extensive attention in the last two decades,but the exisiting studies mostly focused on the Jiuquan Basin which located at the western of the Hexi Corridor and less attention has been paid to the Wuwei Basin in the east.Though analyzing the stratigraphy,heavy mineral,paleocurrent and magnetostratigraphic chronology in Haxi,Gangou,Tiantishan and Guishan section at the southwest of the Wuwei Basin,we combined the results of previous studies in the Jiuquan Basin and Lanzhou Basin to obtain the datas of the heavy minera of the Wuwie Basin and the magnetostratigraphic chronology of the Huangyanghe formations and Xianshuihe formations on the Tiantiishan section,and discussed the relationship among the Wuwei Basin's evolution,the northern of the Qilian Mountains fault zone and the northern of the Tibetan Plateau.The following results were obtained:1.The Paleogene at the southwest of the Wuwei Basin has developed the Xiliugou Formation,Huangyanghe Formation and Xianshuihe Formation from bottom to top,the strata could be classified three sedimentary facies: fluvial,alluvial fan,and lacustrine.2.The demagnetization and rock-magnetism experiments showed that the main remanent magnetization is hematite and magnetite,also has a small amount of magnetic hematite;the secondary remanent magnetization is mainly carried by goethite.3.We found 21 normal magnetic chrons and 24 reverse positive magnetic chrons in the Tiantiishan section,and the magnetostratigraphic chronology ages of the Huangyanghe formations and Xianshuihe formations are respectively dated <40.2Ma to ?36Ma and <27.9Ma to ?26.4Ma.4.All results of heavy minerals,paleocurrents and gravels showed that the sediment's source of the Xiliugou and the Huangyanghe formation is the mountains south of the Wuwei Basin,including the Paleozoic metamorphic rocks and Paleozoic sedimentary-volcanic system,granite and a series of iron ore sites,where are far away from the sections(20km-100 km);the sediment's source of the Xianshuihe formation is a mixed source,including the mountains in the south,southwest and the northwest of the basin,which is similar with the Huangyanghe formation and close with the sections(15km-30km).5?The stratigraphic deposits and material source informations in the southern of the Wuwei Basin reflects that the eastern Qilian Mountains had at least four strong tectonic uplifts during the Eocene to Late Oligocene: the Wuwei Basin developted with the Lanzhou Basin and the Xining Basin at ?53 Ma that indicated the eastern of the Qilian Mountains started to uplift at that time,then Huangyanghe formation started to deposite at ?40 Ma implied it synchronized with the western of the Qilian Mountains;during ?36Ma to 28 Ma the Wuwei Basin in denuded stage,it showed that the Qilian Mountains and the Wuwei Basin uplifted simultaneously,it was probably a response to the uplift of the Tibet Plateau at ?33 Ma;the southern of the Wuwei Basin ended deposition at ?26 Ma,which indicated the fourth uplift thereafter.