Cenozoic Tectonic Uplift And Sedimentary Response In The Western Part Of The Northern Qaidam Basin

The Qaidam Basin,the largest sedimentary basin in the northern margin of the Tibetan Plateau,whose Cenozoic intra-basin sedimentary evolution is closely related to the uplift of the surrounding Mountains and the Tibetan Plateau.The research area is located in the western section of the Northern margin of the Qaidam Basin(WNQB).The mountain is mainly Saishiteng Mountain and Xiaosaishiteng Mountain in this area.Over the years,although extensive petroleum geology studies have been conducted in the WNQB,there has not been a unified understanding of the tectonic evolution process and the law of accumulation and enrichment due to the complicated structure of the basin.Therefore,it is of great economic significance to study the uplift time,the sedimentary evolution history,and their coupling relationship in the WNQB.Based on previous research results,we carried out field geological survey,and combined the new structural geology and sedimentology study to discuss and divide the tectonic period in the WNQB.In addition,the apatite fission-track dating and thermal history simulation,combined with the regional sedimentary records,unconformity records,and the tectonic deformation records,were used to investigate the sedimentation response of the Cenozoic tectonic uplift in WNQB.The main conclusions are as follows:(1)In this paper,apatite fission-track dating were performed on five samples of Mesozoic metamorphic and igneous rocks(obtained in front of the Xiaosaishiteng Mountain)in the WNQB.The cooling ages of the five samples were 27.4 ± 2.0 Ma,29.0 ± 2.0 Ma 32.2 ± 2.3 Ma,32.8 ± 2.0 Ma,and 34.5 ± 2.4 Ma,respectively.These age data are almost identical within the error range and are all Oligocene.A fission-track thermal history simulation of the two samples shows that at least two stages of rapid tectonic uplifting occurred in the WNQB,which were around 12 Ma and 2.5 Ma,respectively.(2)Through the restoration of the balanced profile of three seismic sections of a vertical mountain in the WNQB,it is concluded that the shortening rate of the area is larger since the 12.9 Ma and 2.5 Ma,and the shortening rate since 2.5 Ma to the maximum.(3)Based on the study of the chloride ion content in the Cenozoic sedimentary rocks of the WNQB,it was found that during the sedimentary transitional period(12.9 Ma)from the Lower Youshashan Formation to the Upper Youshashan Formation,and the Quaternary(2.5 Ma)depositional period,the chloride ions content showed a sudden increase,reflecting two tectonic uplift events in the area.(4)The uplift time of the mountains in the WNQB is in good agreement with the sedimentary event time within the basin.At around 12 Ma and 2.5 Ma,the Xiaosaishiteng Mountain strongly uplifted and rapidly squeezed into the basin,resulting in the rapid shortening and uplifting of the late Cenozoic basin,and increased chloride ion content in the formation.(5)The Xiaosaishteng Mountain was quickly raised around 12 Ma,which led to the uplift and sedimentation of the Sugan-Lake Basin,and was separated from the Qaidam Basin;Until the Quaternary(2.5 Ma)period,the Saishiteng Mountain was rapidly lifted up,and the Sugan-Lake basin was strongly settled to accept sedimentation.