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《Geographical Research》 2014-06
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Palaeoflood OSL chronology and its response to climate change in the Yunxi-Yunxian reach in the upper Hanjiang River valley

ZHOU Liang;HUANG Chunchang;ZHOU Yali;PANG Jiangli;ZHA Xiaochun;MAO Peini;ZHANG Yuzhu;College of Tourism and Environmental Sciences,Shaanxi Normal University;Ministry of Education Key Laboratory for Coast and Island Development,Nanjing University;  
The Hanjiang River is the biggest tributary of the Yangtze River and it will supply water resource to Beijing through the national"South-to-North Water Diversion Project".Holocene slackwater deposits along the river channels were used to study the magnitude and frequency of the paleoflood that occurred prior to gaged records and historical datasets all over the world.These pedo-stratigraphic sequences are studied using a multi-discliplinarily approach to reconstruct Holocene hydro-climatic variations.Our field investigations was carried out in the upper reaches of Hanjiang River valley.Four bedsets of palaeoflood slackwater deposit(SWD)were found interbedded in the eolian loess-soil profile at the GXH site,which were identified by the sedimentary criteria and analytical results.Analytical results,including grain-size distribution and magnetic susceptibility,indicate that these SWD consists of sandy silt,sourced from the suspended sediment load of the palaeo-floodwater.Each bedset of the SWD represents one group of palaeoflood event.OSL dating for the quarts grains at different sizes separated from the samples by using the single aliquot regenerative-dose(SAR) protocol.All OSL measurements were made on a Ris? TL/OSL DA-20 dating system using a blue light(470 nm) for optical stimulation.The dose rates were converted and calibrated by using the measured concentrations of U,Th,K elements.The OSL dates were figured out by using the Age.exe software written by Grün(2003).According to the optically stimulated luminescence(OSL) dating method in combination with archaeological dating of retrieved anthropogenic remains,and with pedostratigraphic correlations with the previously studied Holocence pedo-stratigraphy in the upper reaches of Hanjiang River valley,these palaeoflood events were dated to 12500-12000 a(SWD1),7500-7200 a(SWD 2),3100-2800 a(SWD 3),1800-1700 a(SWD 4),respectively.These flooding events are therefore considered to be a regional expressions of known climate events in the northern hemisphere and demonstrate that Holocene climate was far from stable.In the reconstructed temperature time series based on high-resolution climatic proxies from tree-rings,stalagmites,ice-cores and lake sediments across the world,these extraordinary palaeoflood events are well correlated to the decline time of global climatic or climatic transition.Highly unstable climate may result in great variation of precipitation.which can cause floods and droughts.These results are of great significance in mitigating flood disasters,and in hydraulic engineering,as well as in understanding hydrological response to global climatic change.
【Fund】: 国家自然科学基金项目(41030637 41271108 41371029)
【CateGory Index】: P53;P467
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