长江河口水下三角洲沉积物组成变化及其环境意义  

CHANGE OF SEDIMENT COMPOSITION IN THE YANGTZE RIVER SUBAQUEOUS DELTA AND ITS ENVIRONMENTAL IMPLICATIONS

作　　者：颜晨瑶 张卫国[2] 陈莹璐 年小美[2] 胡忠行[1] YAN Chenyao;ZHANG Weiguo;CHEN Yinglu;NIAN Xiaomei;HU Zhongxing(College of Geography and Environment Science,Zhejiang Normal University,Jinhua 321004,Zhejiang;State Key Laboratory of Estuarine and Coastal Research,East China Normal University,Shanghai 200062,Shanghai)

机构地区：[1]浙江师范大学地理与环境科学学院,浙江金华321004 [2]华东师范大学河口海岸学国家重点实验室,上海200062

出　　处：《第四纪研究》2022年第2期412-420,共9页Quaternary Sciences

基　　金：国家重点研究发展计划项目(批准号:2017YFE0107400);国家自然科学基金项目(批准号:41976158和41576094);上海市科委项目(批准号:18DZ1206400)共同资助。

摘　　要：三角洲不同年代的沉积物组成记录了流域-河口-近海沉积物源汇过程动态变化信息。文章以长江河口水下三角洲A3-1和A6-6柱样为对象,进行了光释光(OSL)年代、粒度和元素地球化学分析,探讨了不同年代沉积物地球化学组成差异及其影响因素。研究结果表明,柱样长度为1.58 m的A3-1沉积物年龄为1070±50~1180±30 a(距今约1000~1200年),柱样长度为1.80 m的A6-6沉积物为49±9~198±21 a(距今约50~200年)。柱样A3-1和A6-6元素组成存在显著差异,其中A6-6具有较高的Al、Fe、Mg、K、Ca、Cu、Cr、Co、Cd、V、U和Th等元素含量,而A3-1具有较高的Na和Zr含量。粒度是影响两个柱样元素含量的重要因素,利用Al归一化粒度影响后,柱样A3-1具有高Na和低Ca的特征,以及较低的Cr/Th比值。Ca/Al-Na/Al-Ti/Al三元图也清晰表明了A3-1和A6-6的物源差异。通过与长江主要输沙支流和黄河沉积物元素组成的比较,两个柱样元素组成差异的原因主要有两个:一是长江不同支流对长江沉积物贡献随着时间的变化,其中年龄较老的A3-1沉积物(距今约1000~1200年)更多来自汉江,年龄较轻的A6-6沉积物更多受到嘉陵江影响;二是黄河近千年南迁的影响,距今约50~200年的A6-6沉积物具有高Ca特征,反映了高Ca的废黄河物质对近期长江三角洲沉积的影响。研究表明,河口三角洲沉积物的组成存在动态变化的特征,通过年代和元素组成的分析,可以提供流域和海洋环境变化对三角洲沉积环境演变的控制信息。Delta deposits receives sediment supply from both the river basin and the marine,which can alter sediment composition in accordance with their relative importance.Furthermore,the composition of delta deposits can be influenced by the varying contribution of different tributaries within the river basin as a result of climate change and human activities.Therefore,the time-varying sediment composition of delta deposits contains information on the dynamical process of sediment transport along the catchment-estuary-sea water continuum,which can be used to decipher the complicated delta evolution processes.The Yangtze River is the third largest river in the world,and the huge drainage basin(1.8 million km;)consists of multiple large tributaries(e.g,Jinsha River,Jialing River and Han River).These tributaries contribute to the formation of the Yangtze River delta.Furthermore,the recent southern migration of the Yellow River to northern Jiangsu Province(1128~1185 A.D.)can deliver sediment southward to the Yangtze River delta and participate in the formation of the delta.However,the temporal influence of different tributaries and the Yellow River on the sediment composition of the Yangtze River delta remains poorly studied,although fluvial sediment discharge to the sea by both the Yangtze and Yellow River has fluctuated significantly over the past 1000 years from historical documents and instrumental observations.In this study,core A3-1(31.64°N,122.36°E,water depth 16 m,158 cm in length)and A6-6(30.80°N,122.81°E,water depth 27 m,180 cm in length)from the Yangtze River subaqueous delta has been investigated by Optical Stimulated Luminescence(OSL)dating,grain size and geochemical analyses.Our results reveal that cores A3-1 and A6-6 cover different depositional periods,with the former ranging from 1070±50 a to 1180±30 a,and the latter between 49±9 a and 198±21 a.Such a marked age difference reveals the heterogeneity in spatial deposition.These two cores have significant differences in the compositions of major and tra

关 键 词：元素特征 物源 粒度 时间变化 长江水下三角洲 

分 类 号：P534.632[天文地球—第四纪地质学] P595[天文地球—古生物学与地层学]