Integration Time Of The Yellow River Through The Sanmen Gorge:Insights From A Drill Core Archive

Integration and evolution of the Yellow River and its relationship with the uplift of the Tibetan Plateau and global climate change are frontier scientific issues in the field of earth science.Previous studies mainly focused on the terraces,geological structures and provenance changes of sedimentary record in the middle-upper reaches of the Yellow River,and provenance changes in marginal seas.Although a series of important research progress has been made,there is still disagreement on the age when the modern Yellow River system formed.The estimated ages range from late Miocene-early Pliocene,?5 Ma,?1.6-1.5 Ma,?1.3-1.4 Ma,?1.2 Ma,?0.8 Ma,and ?0.15 Ma.The timing of Yellow River cutting through the Sanmenxia basin and flowing into the sea is an important symbol of the beginning of the formation of the modern Yellow River system.In this study,we drilled a 150 m long high-quality sedimentary cores(SMX19)in Sanmenxia,and established the framework of late Quaternary sedimentary environment change in Sanmenxia by describing lithology,analyzing rock slices,grain size and mineral composition.Through high-precision paleomagnetic dating,the age of the oldest Yellow River sediments was clarified,and thus the age when the Yellow River cuts through Sanmenxia basin and flowed eastward into the sea was determined.Comparing with published results,we discussed the main controlling factors affecting the formation and evolution of the modern Yellow River system.The following main insights were obtained:1)The top(0-9.9m)of SMX19 is loess deposit,the middle(9.9-108.7m)is typical fluvial deposit(including channel deposit and floodplain deposit),and the bottom(108.7-150m)is lacustrine deposit.SMX19 completely records the sedimentary environment evolution process from closed lake to open river in Sanmenxia basin.Based on the evidence of heavy mineral assemblage,it is clear that the fluvial sand at 108.7 m is the oldest Yellow River sediment.2)Paleomagnetic dating results show that the bottom age of SMX19 is ?1.96 Ma,and the oldest Yellow River sediment is ?1.25 Ma.Combined with the published research results of surrounding river terraces,this paper report that the Yellow River cut through the Sanmenxia basin and flowed into the sea at ?1.25 Ma.3)The time of the Yellow River cutting through Sanmenxia basin was much later than the age when the northeast margin of the Tibetan Plateau and the surrounding mountains(Huashan and Zhongtiao Mountains,etc.)accelerated uplift(?8 Ma),but was close to the age when the global sea level decreased rapidly in the early Middle Pleistocene.This suggests that global sea-level change has an important influence on the formation and development of the modern Yellow River system.This study provides direct geological evidence to revealing the formation age of the modern Yellow River drainage system and also provides a new perspective to understand the development pattern of large-scale drainage system.Independent chronology evidence other than paleomagnetism,multiple high-resolution proxy records of paleoclimate,and integrated studies of the Yellow River sedimentary record are the key to explore the formation and evolution history of the Yellow River,drainage pattern,ecological and environmental effects and other important scientific issues.