Characteristics of paleoflood deposits archived in unit T0403 of Yuxi Site in the Three Gorges reservoir areas,China  

作　　者：ZHU Cheng MA ChunMei XU WeiFeng BAI JiuJiang ZHENG ChaoGui ZHU GuangYao WANG HuiLin CHEN Ye LU XueFeng 

机构地区：[1]School of Geographic and Oceanographic Sciences,Nanjing University,Nanjing 210093,China [2]Institute of Cultural Relics and Archaeology,Chongqing 400013,China [3]Department of Geography,Chuzhou College,Chuzhou 239012,China [4]Department of Humanity and Social Sciences,Bengbu College,Bengbu 233050,China [5]School of Geographic Science,Nanjing Normal University,Nanjing 210097,China [6]State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi’an 710075,China

出　　处：《Chinese Science Bulletin》2008年第S1期1-17,共17页

基　　金：Supported by the National Natural Science Foundation of China(Grant No.90411015);the National Science and Technology Support Project(Grant No.2006BAK21B02);the University Doctoral Foundation(Grant No.20050284011);the Foundation of Important Basic Research at Nanjing University(Grant No.0209005206);the Open Foundation of the State Key Laboratory of Loess and Qua-ternary Geology from the Institute of Earth Environment,CAS(Grant No.SKLLQG0503);the Physical Geography of"985"Items and the Test Foundation of Modern Analyses Center of Nanjing University(Grant No.0209001309)

摘　　要：Based on the detailed analyses,multi-proxies such as AMS 14 C dating,grain size,component and morphology of heavy minerals,micromorphology of zircon,magnetic susceptibility,Rb/Sr and Hg content are used to research the paleoflood sediments archived in the Yuxi Site.The research indicates that, since 7.6 kaBP,at least 16 times of paleoflood with water level above Wusong Elevation 147.024 m(a.s.l.) left deposits in the Neolithic layers of unit T0403 from the Yuxi Site.The results are induced from the following aspects:(1)The plaeoflood sediments take on great similarities with modern flood sediments in the Yuxi Site and Zhongba Site in probability cumulative curves which mainly show a pattern of 3 segments in fluvial pattern.(2)There is some resemblance between the heavy mineral components and the zircon shape characteristics of paleoflood deposits and those of modern flood deposits.(3) Magnetic susceptibility values(40.44―70.10SI)are lower than those of sediments from cultural layers (59.59―188.68SI).(4)Hg values(290.71―742.51 ng/g)are lower than those of sediments from cultural layers(344.16―10518.17 ng/g).(5)Rb/Sr values are higher than those of sediments from cultural layers, while those of the 4th,5th,6th,7th,8th cultural layers are high,which shows that they are inundated by paleoflood.The reason for many flood deposits existing is related to the site situated on the first terrace where the Yuxi River joins with the Yangtze River.As there are some similarities between the plaeoflood sediments and those of the Zhongba Site,it is feasible to confirm the existence of paleoflood sediments based on the above points.Based on the detailed analyses, multi-proxies such as AMS 14C dating, grain size, component and morphology of heavy minerals, micromorphology of zircon, magnetic susceptibility, Rb/Sr and Hg content are used to research the paleoflood sediments archived in the Yuxi Site. The research indicates that, since 7.6 kaBP, at least 16 times of paleoflood with water level above Wusong Elevation 147.024 m (a.s.l.) left deposits in the Neolithic layers of unit T0403 from the Yuxi Site. The results are induced from the following aspects: (1) The plaeoflood sediments take on great similarities with modern flood sediments in the Yuxi Site and Zhongba Site in probability cumulative curves which mainly show a pattern of 3 segments in fluvial pattern. (2) There is some resemblance between the heavy mineral components and the zircon shape characteristics of paleoflood deposits and those of modern flood deposits. (3) Magnetic susceptibility values (40.44–70.10SI) are lower than those of sediments from cultural layers (59.59–188.68SI). (4) Hg values (290.71–742.51 ng/g) are lower than those of sediments from cultural layers (344.16–10518.17 ng/g). (5) Rb/Sr values are higher than those of sediments from cultural layers, while those of the 4th, 5th, 6th, 7th, 8th cultural layers are high, which shows that they are inundated by paleoflood. The reason for many flood deposits existing is related to the site situated on the first terrace where the Yuxi River joins with the Yangtze River. As there are some similarities between the plaeoflood sediments and those of the Zhongba Site, it is feasible to confirm the existence of paleoflood sediments based on the above points.

关 键 词：Three Gorges reservoir areas UNIT T0403 of Yuxi SITE CHARACTERISTICS of paleoflood deposits probability CUMULATIVE curve of grain size shape of ZIRCON geochemistry indexes 

分 类 号：P512.2[天文地球—地质学]