• 责任者：Luo Chao (Key Laboratory of Surficial Geochemistry ; Ministry of Education ; School of Earth Science and Engineering ; Nanjing University ; Nanjing 210093 ; China) ; Zheng Yan
• 刊名：Quaternary Sciences
• 出版年：2013
• 卷期：33(4)
• 关键词：悬浮物质 ; suspended materials ; 长江 ; Yangtze River
• 页码：p.684-696
• 图表：6 illus., 76 refs.
• 分类号：1400
• issnNo：ISSN1001-7410
• isbnNo：CN11-2708/P

     Originating from the Qinghai-Tibetan Plateau,the Yangtze River（YR）is the third longest（6300km）river in the world,covering a total area of 1.8×106km2 and locating between 24°30＇~35°45＇N,90°33＇~112°25＇E.It is a key area in the study of ＂Source to Sink＂ processes by serving as a major pathway for erosion products from the continents to the oceans.In this study,we do a preliminary research on magnetic properties of suspended sediments from the main stream and major tributaries of the Yangtze River during flood season of 2011, with the purpose to trace sediment source using environmental magnetic approach. Sampling sites covering a large area of the Yangtze River drainage from Benzhilan in the upper reaches to Nanjing near the estuary and a total of 28 samples were collected. Environmental magnetic measurements were carried out on suspended particular matter（SPM）,including magnetic susceptibility（χ）,anhysteretic remanent magnetization（ARM）,isothermal remanent magnetization（IRM）of all samples and temperature-dependence of magnetic susceptibilities of representative samples. The results are as the following：（1）S-ratio of SPM samples are between 0.83~0.96,in average of 0.86,indicating that the magnetic mineralogy is dominated by low coercivity minerals（magnetite）in all samples,with a small proportions of high coercivity minerals（hematite and goethite）.（2）Variation of HIRM suggests that the anti-ferromagnetic mineral contents of sediments from the upper reaches are higher than those in the middle and lower reaches,which is a reflection of the wildly distributed purple sandstone and shale within the Sichuan basin.（3）Affected by the vanadium-titanium magnetite around Panzhihua,concentration of ferrimagnetic minerals in the main stream increased rapidly near Panzhihua with χ and SIRM arrives to 246×10-8m3/kg and 48833×10-6Am2/kg respectively.The high concentration was followed by a slightly decline downstream with a sharp drop at the Three Gorges Dam（TGD）.This indicates an interception of the TGD on the magnetic minerals from the upper Yangtze River.（4）The high concentration of magnetic minerals in Yalong Jiang,Han Jiang and Xiang Jiang was controlled by the source rocks,industrial and agricultural activities,respectively.（5）χfd% values of most samples are higher than 5%,suggesting the existence of superparamagnetic minerals.According to the variation of ARM/SIRM,grain size of magnetic mineral particles showed a fining trend downstream from source to sink.It is suggested to be determined by catchment lithology,geomorphology and hydrology of the Yangtze River.On the whole,though the magnetic properties of suspended sediment in the Yangtze River can indicate the source information to some extent,they are also controlled by weathering conditions and,in modern settings,anthropogenic impacts（such as TGD）which made this method restricted when applied to provenance studies.