Bedrock Rivers In The Daqing Shan In Inner Mongolia,Northern China

Many of the large-scale rivers in the world follow major tectonic lineaments,and their development records the structural history of the region through which they flow.The 5464 km long Yellow River is the second longest river in China.Previous studies have suggested the integration of the Yellow River as a result of the late Cenozoic tectonic uplift in the northeastern Tibetan Plateau,as well as rifting around the Ordos Block.Deciphering the Yellow River’s response to tectonic disturbance has the potential to provide important constraints on the tectonic evolution of the northeastern Tibetan Plateau and rift basin group around the Ordos Block.In addition,the Yellow River is notable for an extremely high silt content and sediment discharge so that it can provide a lot of material for the Chinese Loess Plateau,the North China Plain and continental shelf.Thus,understanding the integration of the YR is crucial to reveal the origin of the Chiese Loess Plateau and the formation of the North China Plain and continental shelf.Although many previous works have been paid to different reches of the Yellow River,there is a lack of good research to link evolution processes at different reaches.Many studies revealed the incision and integration of the Yellow River in the northeastern Titbet Plateau since early Pleistocene.Craddock et al.(2010)suggested a fluvial incision signal initiated at the northeastern margin of the Tibetan Plateau ～1.8 Ma ago and then progressed upstream to excavate and integrate a series of intermontane basins along the Yellow River course,such as the Linxia,Xunhua,Guide,Gonghe,and Tongde Basins.However,this integration process significantly postdated the initiation of widespread mountain building(～10 Ma)and antedated recent uplift(1.2-0.8 Ma)across the northeastern Tibetan Plateau.That indicated the late Cenozoic tectonic uplift of the northeastern Tibetan Plateau was not the main forcing for the integration of the Yellow River in the northeastern Tibetan Plateau after ～1.8 Ma.On the other hand,the enhanced aridification in the course of the Yellow River during the Quaternary is less supportive for that the lake expansion and spillover into downstream basins initiate fluvial incision.Thus,a new possible mechanism that can trigger this incision signal at the northeastern margin of Tibetan Plateau ～1.8 Ma ago should be explored from further downstream reaches.The Hetao Basin,a rift basin in the northern part of the Ordos Block in Inner Mongolia,northern China,was the key junction between the upper and middle reaches of the Yellow River.The thick late Cenozoic sediments and the normal faulting of the bounding faults indicate that the Hetao Basin has been in a state of extensional deformation since ～ 10 Ma,responding to the far-field effect of the northeastward growth of the Tibetan Plateau or the northwestward subduction of the Pacific Plate.Meanwhile,the continuous lowering of the Hetao Basin may inhibit that some incision signals from the middle and lower reaches of the Yellow River migrate to the upper reaches.Many studies indicated that the connection between the Hetao Basin and the middle and lower reaches was established after 1.5 Ma.The Hetao Basin controlled the erosion base level of the upper Yellow River before 1.5 Ma.We thus speculated the late Cenozoic extensional rifting in the Hetao Basin triggered integration of the upper Yellow River.In order to test this hypothesis,we explore the tectonic mechanism that can drive headward erosion along the Yellow River and the timescales over which it occurred by reconstructing the late Cenozoic tectonic history in the Hetao Basin.We applied geomorphology,bedrock channel form and late Cenozoic sedimentary strata in the Daqing Shan to explore the late Cenozoic tectonic evolution in the Hetao Basin.Then,we combined with the provenance analysis of early Pleistocene strata in the Hetao Basin to discuss the connection between the late Cenozoic tectonic evolution in this region and the integration of the upper Yellow River.Based on the above research,we revealed the late Cenozoic tectonic history of the Hetao Basin and further discussed its effect on the evolution of the Yellow River.We draw the following conclusions:(1)the pattern of tilted uplift is recored by geomorphic characteristics and bedrock channel form.(2)sediment flux affect abviously basin erosion processes in the Daqing Shan.When we constrain a mean erosional efficiency K by the relationship between erosion rate and channel steepness index,we cannot neglect the effect of sediment flux.(3)the accelerated vertical slip between the Daqing Shan and the Hetao Basin initiated at 2.8 ± 0.8 Ma,and the average relative uplift rate was 0.18 ± 0.04 mm/yr since 2.8 Ma.(4)the lowering of erosion base level in the Hetao Basin since 2.8 ± 0.8 Ma produced a headward erosional signal along the Yellow River that initiated fluvial incision at the northeastern margin of the Tibetan Plateau ～1.8 Ma ago.The results of this study indicate that the accelerated extensional deformation in the Hetao Basin has been responsible for the integation of the upper Yellow River since the late Pliocene.