Sedimentary Environment Analysis Of Niubao Formation-Ding Qinghu Formation In Duoma Area, Shuanghu, Northern Tibet

This paper studied the Paleogene-Neogene Niubao Formation and Dingqing Lake Formation in Doma Township,Shuanghu County,Tibet,mapped large scale plots,measured stratigraphic profiles,and detrital zircon U-Pb dating.By means of others,combined with predecessors' existing research data,the depositional environment,age,and contact relationship between the Niubao Formation and the Dingqinghu Formation were discussed.The Lunpola Basin is a new-generation terrestrial sedimentary basin developed on the Bangong Lake-Nujiang suture zone in central Tibet.The area of the discussion is located in the northwestern part of the Jiangria Fault Sag in the Lunpola Basin,Tibet.At the end of the Yanshanian period,under the mechanism of the collapse after the mountain building,the surface crust of the crust was stretched and rifted,forming an intra-basin faulted basin.The Paleocene-Eocene Niubao Formation,Oligocene-Miocene Dingqing Lake Formation have been deposited.Its depositional environment is a closed lacustrine deposit.During the period of the Old Eocene,a north-south thrust nappe structure system was developed.The north boundary of the basin sediment distribution area was fault control,and the fault was a northward thrust fault.A strong fracture zone was formed,and the affected Paleogene Niubao Formation(E1-2n)was strongly deformed,while the D3-Qing Lake Formation(E3-N1d)strata deposited above the Niubao Formation was very gentle,reaching a near-horizontal level..This study is based on five observed profiles of the Niubao and Dingqing Lake Formations of the Paleogene,combined with detrital zircon U-Pb dating.The main understanding is that:(1)Put forward a new understanding of the contact relationship between the Niubao Formation and the Dingqinghu Formation.(X:739011.797904 Y:3546505.227137)It can be seen that there is an angular unconformity contact between the two.(2)Using LA-ICP-MS detrital zircon U-Pb dating,the age of the second member of the Niubao Formation is 43.6±0.6Ma,and the age of the second member of the Dingqinghu Formation is 23.3±0.4Ma.(3)The sedimentary environment and sedimentary facies,subfacies and microfacies of the Niubao Group and Dingqinghu Formation are divided.A total of 3 sedimentary facies,including lacustrine facies,braided facies delta facies,and fan delta facies,were identified.