Late Pleistocene Sedimentary Evolution And Geological Significance Of Hongsibao Basin On The Northeast Margin Of The Tibetan Plateau

The Hongsibao Basin on the northeastern margin of the Qinghai-Tibet Plateau is a late Pleistocene intermountain basin sandwiched between the Niushoushan-Luoshan tectonic zone and the Yantongshan tectonic zone on the outermost side of the arctic structural zone on the northeast margin of the Tibetan Plateau.,Its unique sedimentary feature is to reshape the window of the late Pleistocene tectonic evolution and climate change in the northeastern margin of the Tibetan Plateau.Based on systematic route geological survey,combined with high-precision dating methods such as OSL and ¹⁴C and analysis of clay minerals in typical sections,this paper discusses the late Pleistocene sedimentary evolution and its geological significance in Hongsibao Basin.The main achievements and understandings are as follows:1.By dividing and comparing sedimentary cycles,the original Sarawusu Formation in the Hongsibao Basin is divided into two sedimentary cycles.The lower cycle is equivalent to the original Sarawusu Formation and the upper cycle is equivalent to the Shuidonggou Formation in Ningxia.The Malan loess is mainly distributed in the foothills of the adjacent structural belt of the basin,and has a phase-change contact relationship with the Shuidonggou Formation,and an overlapping contact relationship with the Sarawusu Formation.2.Based on the division and comparison of the sedimentary cycles of the basin,combined with OSL dating and ¹⁴C dating,the late Pleistocene stratigraphic framework of the Hongsibao Basin was constructed:the formation age of the Sarausu Formation in the Hongsibao Basin is about 140Ka-54Ka BP,the age of the Shuidonggou Formation is about 32Ka-11Ka BP,and there are about 22,000 years of sedimentary discontinuities between the two.3.The Hongsibao Basin developed three-stage alluvial fans during the Late Pleistocene deposition process,respectively responding to the three-stage tectonic uplift of the adjacent tectonic belt since the late Pleistocene.The first-stage uplift may occur between 119Ka-140Ka,the second-stage tectonic uplift may occur around 79Ka,and the third-stage tectonic uplift may occur around 54Ka.4.Preliminary analysis using clay mineral analysis revealed that the Late Pleistocene of Hongsibao Basin experienced a warm-humid-cold arid-warm-humid-cold arid climate change process.The content of chlorite is relatively low,while the content of montmorillonite and kaolinite is relatively high,showing warm and humid paleoclimate characteristics,which correspond to the deep ocean oxygen isotope curves MIS3 and MIS5 stages,respectively,and have global significance.5.Guided by the idea of basin-mountain coupling,combined with geophysical exploration results,it is found that there is a hidden paleo-uplift in the Hongsipu Basin,controlled by the Yantongshan fault system on the west side of the basin,which has a unified stress field background and formed at the end of Neogene sedimentation,controlled the sedimentary evolution process of the basin in late Pleistocene.