The Variations Of The Cenozoic Sedimentary Flux Of Jiuxi Basin In Northeastern Tibetan Plateau And Its Main Controlling Factors

Orogenic belts and sedimentary basins are two basic geological units of continent,which supposed to be in strong relationship between tectonic evolution and forming mechanism,this symbiotic relationship is known as mountain-basin coupling.The intensified Tectonic deformation driven the accelerated uplift of mountain ranges,as a result,the source area suffered stronger weathering and erosion.At last,the stripped material deposited in the basin by means of the force of flow?wind?glacier and so on.For this reason,the sedimentary basin not only record the characteristics of Orogenic belts but also the Environmental Characteristics.The Jiuxi basin lies at the western portion of Hexi corridor of Northern Tibetan Plateau magin contains thick and continuous sequence of Cenozoic sedimentary rock.This sequence contains considerable information on the history of Tibetan uplift and associated climate change.In recent years,our research group did plenty of work at Jiuxi basin,reported on a detailed paleomagnetic study of Jiuxi basin,and set a good foundation to refine the tectonic history and climate change of this area.Trough field investigation and profile measurements at different sites of Cenozoic Jiuxi basin,combined with seismic cross-section and drilling data,we obtained the the periphery and tectonic features of Cenozoic Jiuxi basin by utilizing Restoration of balanced cross section of Cenozoic Jiuxi basin.On the basis of aforementioned measurements,we compiled the isopach map of Cenozoic Jiuxi basin.The isopach map indicates the variations of sediment flux at diffrent epoch.By synthesizing with other records of Cenozoic tectonic evolution and paleoclimate,we probe into the main factors that lead the change of sediment flux of Cenozoic Jiuxi basin,and discuss the relationship with denudation of basin-bounded mountain.This study throws lights on the interation of tectonic uplift-climate change-Weathering and erosion.We got conclusions as follow:(i)Restoration of balanced cross section across the Jiuxi basin suggests that:the periphery of Cenozoic Jiuxi basin diminish by the time,and suffered two stages of rapid tectonic period and two stages of tectonic quiet period.Cenozoic shortening strain is highly inhomogeneous,varying from 7.18%to 38.27%.From early Cenozoic to Oligocene,the shortening amount,shortening strain and shortening rate are 1.49Km,7.18%and 4.37 cm · ka-1 respectively.By the time of 30.9 to 23 Ma,the shortening amount?shortening strain and shortening rate are 3.66Km?17.64%and 46.33 cm · ka-1 respectively.By the time of 23 to 8.3 Ma,the shortening amount?shortening strain and shortening rate are 7.66Km?36.91%and 52.11cm · ka-1 respectively.From early 8.3 to present,the shortening amount?shortening strain and shortening rate are 7.94 Km?38.27%and 95.66cm · ka-1 respectively.The tectonic deformation intensified significantly by 8.3Ma.(ii)The variation of isopach map and sediment flux of Cenozoic Jiuxi basin suggest:for Huoshaogou formation(40.2-33.4 Ma),the isopach map primarily oriented parallel to the NE-trending Altyn-Tagh fault.In contrast to Huoshaogou formation,the isopach map of Baiyanghe formation(30.8-23.8 Ma)oriented parallel to the WE-trending northern Qilian Shan.The sediment flux increased sharply from 31.78Km3/Ma to 256.2Km3/Ma at this time interval.The distribution style of isopach map of Sulehe formation is the same as Baiyanghe formation,while the depocenter migrated southward.Sediment flux was relatively low(73.24 Km3/Ma)at early-middle Miocene Gongxingshan unit(23-14 Ma),and increased rapidly at Getanggou unit(14-8.3Ma),Niugetao unit(8.3-4.9 Ma)and Yumen formation(3.66-0.93 Ma),the sediment flux are 185.99 Km3/Ma,316 Km3/Ma and 387.15 Km3/Ma respectively.(iii)The increase of sediment flux of Huoshaogou formation and Baiyanghe formation is attributed to the Continuous indentation of India into Asia,driving the upward and outward growth of Tibetan Plateau.Nonetheless,the early Miocene appears to be a tectonically quiet period,,as a result,the sediment flux was relatively low during this time interval.For middle Miocene,The increase of sediment flux of Sulehe unit and Getanggou unit is responsible for the humid climate and tectonic activities.For late Mioocene,The increase of sediment flux of Niugetao unit and Yumen formation is attributed to the growth of the northern Qilian Shan.