【作者】 陈锦山；

【导师】 何青；

【作者基本信息】 华东师范大学 ， 港口、海岸及近海工程， 2011， 硕士

【摘要】 在流域人类活动不断加剧、入海泥沙通量日益减少的背景下,寻求河口海岸泥沙运动与地貌演变规律的主控因子,仍需要从流域泥沙来源及组成变化着眼。人类活动对流域水沙输移的影响范围正在扩大,涉及到干流及其主要产沙支流。获得大面积、高质量的样品进行分析,是研究上述问题的基础。本文基于金沙江石鼓至长江河口的流域大面积沉积物采样,结合粒度测量、磁学测量、粒级分离实验和数学统计方法,将长江流域地表侵蚀与河流输沙作为一个系统,分析沿岸表层土壤、支流、干流及长江口沉积物的磁性特征,探讨长江干流沉积物的来源及组成变化,得到主要认识如下：1.长江流域表层土壤、支流沉积物、干流及长江河口沉积物的磁性特征：通过测量研究区域从金沙江石鼓至长江河口(99°E至122°E,25°N至32°N)大面积的表层土壤、16条主要支流的沉积物、长江干流沿程数个站位沉积物及长江口沉积物的磁性特征,结果表明,表层土壤的磁化率x在9-1955×10-8m3/kg之间,饱和等温剩磁SIRM在2136-235654×10一6Am2/kg之间,非磁滞剩余磁化率χARM范围为23-8185×10一m3/kg,硬剩磁HIRM范围为15-7716×10一6Am2/kg,频率磁化率系数xfd%在0.9--15%之间,反映磁性矿物类型的S-300在40-100%之间,指示磁性矿物晶粒大小的χARM/SIRM范围为0.06-1.44×10一3m/A；主要支流、干流以及长江口沉积物的x在2.2-665.1×10-8m3/kg之间,SIRM在192-84820×10-6 Am2/kg之间,χARM范围为4.9～1600.5×10-8m3/kg, HIRM范围为37-1578×10一6Am2/kg,χfd%在0.1-11.4%之间,S-300在75-100%之间,χARM/SIRM范围为0.07-1.35×10-m/A。以磁化率大小比较,表层土壤磁性比河流沉积物强；流域上游支流及干流沉积物磁性要高于流域中下游支流及干流；长江北岸支流沉积物磁性总体强于南岸支流沉积物。2.长江流域表层土壤及河流沉积物的磁性差异及原因分析：表层土壤和河流沉积物的磁性特征主要由母质控制。峨眉山玄武岩在长江上游地区广泛分布,玄武岩属基性火山岩,亚铁磁性矿物含量高。金沙江、雅砻江、大渡河、岷江和牛栏江等支流下游位于玄武岩广泛分布的区域,沉积物继承了母岩的磁性特征,因而磁性较强。从嘉陵江、乌江流域的沉积岩发育而来的紫色土和南方红壤,具有较多的不完整反铁磁性矿物,涪江、嘉陵江、赤水河、乌江及干流上游沉积物的不完整反铁磁性矿物同样较高。汉江流域上游分布着超基性岩、板岩和片岩,下游岩石由沉积岩、片岩和少量碳酸盐组成。这些岩类中磁性矿物的含量不是很高,但在成土过程中形成一定量的亚铁磁性矿物,亚铁磁性矿物的相对贡献大,因此汉江沉积物具有较高的S-300值。中下游干流、湘江、沅江、赣江以及抚河等,河床基岩主要为花岗岩、板岩、沉积岩和碳酸盐,花岗岩主要为长石和石英,原生磁性矿物含量极低。中下游河流沉积物的磁性也非常低。与河流沉积物相比,流域上游的表层土壤除了接受母岩良好的“本底”外,风化过程中生成大量的细粒磁性矿物,使得表层土壤的磁性要高于河流沉积物。3.长江干流沉积物的磁性特征沿程变化过程及其对物源的指示意义：干流上、中、下游沉积物中磁性矿物类型和晶粒大小沿程变化不大,但磁性矿物含量沿程呈阶梯状减小,其中上游至中游河段沉积物的磁性矿物含量减幅最大。三峡蓄水拦沙是造成干流上游与中下游沉积物磁性差异的主要原因。干流沉积物的磁性受多源性影响,表现为沿程物源差异和粗细不一沉积物来源差异。地表侵蚀对于干流上游部分河道细粒沉积物的来源起主要贡献。金沙江作为主要输沙支流之一,其细粒组分随水流输运的距离更长,并控制干流中游沉积物细颗粒组分的磁性特征,往下游磁信号衰减,岷江、嘉陵江、乌江和两湖等沉积物细粒组分对长江中下游沉积物细粒组分的贡献相对增大。汉江沉积物对长江下游沉积物的磁性特征的影响明显,且主要集中粗颗粒组分。长江河口沉积物的磁性特征与干流沉积物相似程度较高,反映了沉积物“源一汇”过程。其中,中下游河道及两湖一江对于河口沉积物的来源起到重要的贡献。更多还原

【Abstract】 Under the background of intensification of human activities in the Yangtze Basin and declining sediment load into the sea, to seek the host factors which impact the sediment transport dynamic and morphology evolution in coastal zone, it still need to focus on sediment source and composition change first. Human activities, including land use and intensification, influence sediment load in the Yangtze Catchment more than before, even the main stream and tributaries involved.Wide-range, high-quality samples for analysis, is the basis of such research work. With particle size measurement, magnetic measurement, grain size separation experiment and statistical methods combined, considering surface soil erosion and fluvial sediment transport process as a system, analyzing magnetic characteristics of topsoil, fluvial sediment and estuarine sediment, this study will discuss the source and the composition changes of the Yangtze River sediment. The main conclusions are showed as follows:1 The magnetic properties of topsoil, sediment from tributary, mainstream and estuary at the Yangtze Basin:The result of magnetic measurement of topsoil and sediment which taken from Jinshajiang (Shigu) to Yangtze Estuary, show that x values of topsoil are 9～1955* 10-8m3/kg, SIRM values are 2136～235654*10-6Am2/kg, XARM values are 23～8185* 10-8m3/kg, HIRM values are 15～7716*10-6 Am2/kg, S-300 values are 40～100%, Xfd% values are 0.9～15%, XARM/SIRM values are 0.06～1.44*10-3m/A. The x values of fluvial sediment are 2.2-665.1*10-8m3/kg, SIRM values are 192～84820*10-6Am2/kg, XARM values are 4.9～1600.5*10-8m3/kg, HIRM values are 37～1578*10-6Am2/kg, S-300 values are 75-100%, Xfd% values are 0.1～11.4%, XARM/SIRM values are 0.07～1.35*10-3m/A. The result indicates that much difference of magnetic properties within all samples exists. The content of magnetic minerals in topsoil is much higher than that in sediment. Besides, the content of magnetic minerals in sediment from upper basin is much higher than that in sediment from lower basin. The sediment from northern basin have much more magnetic minerals than that from southern basin.2 A discussion of magnetic properties of fluvial sediment and topsoil:Basalts are widely distributed around the upper basin and provide a good "background". Therefore, the content of ferrimagnetic minerals of fluvial sediment and topsoil in this region are very high, such as fluvial samples from Jinshajiang river, Yalongjiang river, Daduhe river, Minjiang river, Niulanjiang river. Purple soil and Southern red earth provide abundant of anti-ferrimagnetic minerals in the Jialingjiang and Wujiang basin, respectively. So HIRM values of the sediment from Chishuihe river, Wujiang river, Jialingjiang river and Fujiang river are relatively high. Granite, slate and carbonate rock are the primary rock type in the middle-lower basin, with low magnetic mineral content. As a result, magnetic mineral contents of downstream tributaries’sediment which are taken from Xiangjiang river, Yuanjiang river, Ganjiang river and Fuhe river are low too.3 The longitude change of magnetic properties of fluvial sediment along the mainstream, and its implication for the provenance identification:From upper reach to lower reach, the type and grain size of magnetic mineral change little. However, magnetic mineral’s content decreases gradually. TGD’impact is the main factors which control magnetic mineral’change. Based on magnetic properties of bulk sample,<63μm fraction and>63μm fraction, using Q-mode cluster analysis, combining with corresponding physical process, to discuss the main source of Yangtze River sediment. The result indicates upper reach area (Nanxi station && Jiangjin station), magnetic properties of its bulk sample and<63μm fraction, are similar with topsoil along the river bank. It indicates that topsoil play a important role to the source of mainstream sediment. Jinshajiang river is the main source of Yangtze River sediment.<63μm fraction of Jinshajiang sediment can influence magnetic properties of middle reach’s fine sediment to a large extent. Then, Minjiang, Jialingjiang, Wujiang rivers, Dongting Lake and Poyang Lake’fine-grain sediment make a relatively increasing contribution to fine-grain sediment of middle-lower reach. Hanjiang river sediment’s imput, have a significantly impact on the low reach sediment (mainly coarse-grain).更多还原