Study And Significance Of Light - Emitting Dating Of The First - Grade Terrain In The Upper Reaches Of The Hanjiang River

Loess, which containes key information of the climate variation during Quaternary period, is one of the three major carriers for climate research. The upper reaches of Hanjiang River area is located at the south side of Qinling Mountains.It is also the climate transition zone of the South and North China and can be extremely sensitive to one slight change of the environment. The loess deposited on the first river terrace involves all kinds of landform evolution and climate fluctuation.The primary problem of this research is to build the robust chronological sequence. However, At present no relevant chronological information of this area is forthcoming. It causes certain difficulty on the analysis of the formation of loess deposition on the river terrace. Therefore, this research picks 4 profiles of first terrace along the upper Hanjiang valley from Ankang to Yunxian and 1 typical profile which located in the midline of South to north water diversion project as well as the tributary of the Hanjiang River— Danjiang terrace to conduct research. Approperate dating method and suitable analysis conditions were chosen according to different samples during optically dating. Moreover, verifying the reliability of the final equivlent dose of different samples. Trying different dating methods to solve the age problems of partial samples which deposited at the bottom of the terrece which show low saturated level of growth curve. The main conclusions are as follows:(1) Single aliquot regenerative method (SAR) and infrared method after blue lights method (Post-IR) are suitable for the upper reaches of Hanjiang River sample test. The dominate signal of these methods are fast componet. However, The TT-OSL method which mainly provided by thermally transferred signal is not inappropriate for the upper reaches of Hanjiang River quartz sample dating on account of the dim signal stimulated during the bleaching process.(2) Both 40～63μm (medium size grain) and 90～125 μm (course grain) particle size of loess samples can be used for the upstream of the Hanjiang River samples dating; 40～63 μm particle size grains show higher saturated level than 90～125 μm grains and offer satisfied results for samples which deposited at the bottom of the terrece.(3)The upper reaches of Hanjiang River terraces were formed earlier than 55 ka B.P., representing the terrace began to form and start to accept aeolian sediment from near source and the north of desert during that time period. The formation of upper reaches of Hanjiang River terrace recorded climate change and evolution of landforms since the last glacial.(4)The loess sequence of upper reaches of Hanjiang River terraces reflect the climate fluctuation of the Last Glacial and the Holocene.During the last glacial period, the upper reaches of the Hanjiang River area was dry and cold and the climate fluctuated frequently.The development of sand-loess periodic interlayer deposited at the bottom in LJT and MTS sections were directly reflections of climate variation. The Holocene could be divide into three different climate period:early Holocene at around 11.3～8 ka B.P.; Holocene optimum at about 8～3 ka B.P; late cooling Holocene period since 3 ka B.P. The CFC section recorded 6～5 ka climate deterioration and developed loess layer in palesol; an ancient flood event happed during atound 0.38 ka and slack water deposits layer developed in HJP section.