The Magnetostatigraphy Study Of The Thickest Lanzhou Loess

The Quaternary loess plays an important role in the study of the global climate change and the earth's magnetic field research.In the past 30 years,the Chinese loess has been throughly studied,and a lot of intergrated magnetic polarity sequences have been yielded.However,several research hots such as the source area of the Loess,the oldest age boundary and its climate significants is still poor known.Furthermore,most of the studies are focus on the east part of the China Loess Plateau(CLP).Hence,it is necessary to carry out more detailed studies of the loess,especially the west part of the CLP,to yield more accurate evidences.Lanzhou locates in the Western arid region,the Eastern momsoom area and the Qinghai-Tibet Plateau cold area,which is the most sensitive area of climate change.Several geologists have done some research work in this region.However,Because of the limitation of the research purpose and technical conditions,the accuracy ages of the Loess deposition is still not determined.Therefore,We carry out a scientific drilling project in the Xijin village(N:36°00'59.35";E:103°44'49.58")at August 2012,which is the highest place of Lanzhou City.The drilling depth is 424.55 m and finally 416.20 m loess coring is yielded.Based on the high-resolution sampling,we do the magnetic research of the drilling stratigraphy.The finally results are in the following:1.The bottom age of the Lanzhou loess core is about 2.20 Ma.The B/M boundary locates at 191.205 m in the drilling stratigraphy(in the low part of L8),and the bottom boundary of eolian loess is in 413.29 m(2.18 Ma).2.Based on the high precision magnetostratigraphy age constrain,the average sedimentation rate of the loess drilling(in Xijin,Lanzhou)is calculated and about 18.92cm/ka,which is higher than the others in the east part of CLP,and would be the most ideal materials for research the Quaternary science.3.Wuquan conglomerate is wide distributed in the Lanzhou,which contains important informations of the formation and evolution of the Yellow River and the uplift of the Qinghai-Tibet Plateau.The Lanzhou Loess angular unconformity overlies on it.Because the buttom boundary of loess in Lanzhou is 2.20 Ma,the top boundary of Wuquan conglomerate should be older than 2.20 Ma.