Sedimentary Evolution And Its Tectonic Significances Of The Pali Basin In Yadong County,Southern Tibet

The Pali basin is located in the southernmost part of the Yadong-Gulu rift valley,and exposed a set of the late Cenozoic sedimentary strata which records tectonic evolution process of Yadong-Gulu rift valley.In addition,the strata can also reflects the development evolution of nearly N-S trending rift system in southern Tibet and the characteristics of the plateau uplift,This dissertation analyzes the sedimentary characteristics,sedimentary facies,paleomagnetism of the late Cenozoic sedimentary strata in detail,on the basis,divided the sedimentary evolution stage.Finally,the dissertation analyzes the tectonic significance of the sedimentary evolution.The main results are as follows:1.The contact relationship of the lower sand-clay layer and the higher elevation sand-gravel layer: both the lower sand-clay layer and the higher elevation sand-gravel layer developed a set of light yellow sandstone,In addition,their occurrence is dip N consistently.So,the lower sand-clay layer underlying the higher elevation sand-gravel layer.2.Based on the lithologic characteristics and sedimentary structure,the thesis recognized three facies,including lacustrine facies,lacustrine fan delta facies and alluvial fan facies.The lacustrine facies are developed mainly in the lower part of the exposed strata;The lake fan delta facies developed in the middle,including progradational lake fan delta facies and retrogradational lake fan delta facies;and the alluvial fan facies developed at the top of the exposed formation.3.The result of the paleomagnetism indicates that the strata formed in 7.5-2.5 Ma.But the bottom strata were not exposed,show that the Pali lake basin has been developed before 7.5 Ma.A set of alluvial fan gravel layer(thickness > 100m)was developed in 2.5 Ma,marking the demise of the lake basin.4.According to the sedimentary characteristics and the results of the paleomagnetism,the sedimentary evolution of the Pali basin can be divided into five sedimentary stages,namely,the initial formation stage(about 13 Ma),the lake expansion stage(> 7 Ma),the Lake shrinking stage(7-3.5 Ma),the lake expansion phase again(3.5-2.5 Ma)and the lake extinction stage(< 2.5 Ma).5.The basin sedimentary evolution combines with the data of the plateau uplift and nearly N-S trending rift system,The dissertation suggests that the peak of nearly N-S trending rift system formation and development is about 13 Ma;The basin and its adjacent region tectonic activity is not strong around 7.5-7 Ma;During 7-3.5 Ma,the tectonic activity is strong in Pali basin,Kung Co-Tangra Yumco rift,Cona-Oiga rift and Dinggye-Xainza rift,indicates that 7-3.5 Ma is the further development period of nearly N-S trending rift system;The change of sedimentary pattern shows that the basin was in a strong tectonic activity about 2.5 Ma,Linked to the plateau climate significantly changed in about 3 Ma,indicating that 2.5-3 Ma is a period of the plateau strongly uplift,and then the plateau had arrived a height which could change the climate.