粤北小流域河漫滩沉积物的粒度与磁性特征及其古洪水识别意义  

Grain Size and Magnetic Characteristics of Floodplain Sediments in a Small Watershed at Northern Guangdong:Implications for Paleoflood Identification

作　　者：林悦敏 欧阳婷萍 李明坤 贺辰戋 张丽容 李桑 Lin Yuemin;Ouyang Tingping;Li Mingkun;He Chenjian;Zhang Lirong;Li Sang(School of Geography,South China Normal University,Guangzhou 510631,China;State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China)

机构地区：[1]华南师范大学地理科学学院,广州510631 [2]中国科学广州地球化学研究所有机地球化学国家重点实验室,广州510640

出　　处：《热带地理》2023年第6期1021-1036,共16页Tropical Geography

基　　金：国家自然科学基金项目(41977261):华南多金属矿区周边农业土壤重金属污染的磁学响应。

摘　　要：随着全球气候变化加剧,台风和强降雨等导致的洪涝灾害频发。如何在沉积记录中有效识别洪水事件,对于查明洪水频发规律具有重要意义。文章对粤北小流域的河漫滩沉积断面(秀丰断面)的沉积物进行了系统的粒度分析和磁性测量,深入分析洪水期沉积层和平水期沉积层不同的粒度和磁学特征,试图为沉积记录的古洪水识别提供新途径。结果表明:(1)沉积物粒度组成主要为粉砂,从洪水期沉积层往平水期沉积层有变细的趋势。其中,洪水期沉积层识别出3层含砂量和平均粒径(Mz)表现为较高峰值的洪水事件记录。(2)不同沉积层中磁性矿物的组成和来源基本一致,以磁铁矿为主,含有部分赤铁矿。矿物来源除流域内母质自然风化产物外,还包含大宝山尾矿库的输入。(3)沉积物主要为悬浮沉积,前汛期持续的长期高水位有利于沉积物分选和沉积,导致处于洪水期沉积层的磁性矿物偏细;随着水动力的增强,洪水期沉积层中识别出的3个洪水事件记录中细粒磁铁矿和赤铁矿含量从河漫滩中部向顶部方向依次增加,同时磁性颗粒粒径变粗。因此,结合磁性参数与对磁性矿物组分的分析能更准确地识别洪水事件。研究区域细颗粒磁铁矿和赤铁矿对饱和等温剩磁的贡献高值叠加粗颗粒磁铁矿贡献降低的磁学特征可作为识别洪水事件及水动力加强的指标。With the intensification of global climate change,floods caused by typhoons and heavy rainfall occur frequently.It is important to effectively identify flood events within sedimentary records to study the flood frequency patterns.Currently,grain size analysis is the commonly applied method for flood event identification.The hydrodynamic conditions and sediment sources identified from the grain size parameters are used to distinguish flood events.However,identification results from a single index can easily lead to inaccuracies due to complex river sedimentation processes.Therefore,it is necessary to select the most suitable proxy and,in combination with the implications of different types of indicators,identify flood events in study areas.In addition to grain size analysis,the technology of environmental magnetism has been widely applied in the sedimentology research of flood sediments owing to its advantages of sensitivity,rapidity,economy,and non-destructiveness.In this study,a longitudinal floodplain sediment profile collected from a small watershed in northern Guangdong was selected as the research object.Both grain size and magnetic characteristics of the entire profile were determined in detail.Based on the flood event records identified by sediment grain size characteristics,an indepth analysis of the magnetic characteristic differences between the flood sedimentary layers and normal sedimentary layers,was performed.We aimed to establish a set of suitable magnetic parameters for identifying flood events in this region.Consequently,a new approach can be used to identify paleofloods within sedimentary records.The results indicate the following.(1)The sediment particle size composition is primarily composed of silt,which accounts for more than 70%of the total.Moreover,the sediment particle size tended to become finer from the flood sedimentary layer to the normal sedimentary layer.Three sublayers characterized by relatively high peak values of sand content and mean grain diameter were identified as flood even

关 键 词：河漫滩沉积物 粒度 磁性特征 古洪水识别 粤北小流域 

分 类 号：P318[天文地球—固体地球物理学] P532[天文地球—地球物理学]