崇明岛H12孔百年来长江入海沉积物来源变化及原因  

Provenance Tracing of Sediment in Changjiang Estuary in the Past 150 Years and the Implications:Case study in core H12 at Chongming Island

作　　者：段知非 李超[1] 毕磊[1] 何中发 李芳亮[1] 杨守业 DUAN ZhiFei;LI Chao;BI Lei;HE ZhongFa;LI FangLiang;YANG ShouYe(State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092,China;Shanghai Institute of Geological Survey,Shanghai 200072,China)

机构地区：[1]海洋地质国家重点实验室(同济大学),上海200092 [2]上海市地质调查研究院,上海200072

出　　处：《沉积学报》2020年第6期1204-1214,共11页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(41676035)。

摘　　要：地质历史时期长江入海沉积物的来源和组成特征是探讨东亚边缘海地区沉积物"从源到汇"过程的核心问题之一。崇明岛H12钻孔沉积物元素与同位素地球化学分析揭示,Nd同位素、Eu异常、Cr/Th、Sc/Th等指标在1858—1906年间明显波动,波动的年份与文献记载的洪水事件发生时间基本一致;而在1906年之后沉积物中以上各地球化学指标趋于稳定。结合长江不同支流的沉积地球化学组成特征,运用物源混合模型进行判别,结果显示过去150年来长江入海沉积物主要来自上游支流及汉江,不同支流的洪水信号可以通过入海沉积物通量和化学组成来提取。20世纪以来H12钻孔沉积的各物源指标波动明显减小,推测与崇明岛当地的人类活动逐渐增强有关,防护堤、海塘等工程修建改变了长江入海沉积物在崇明岛的沉积方式,使得洪水时期沉积物无法在岛上淤积,因而钻孔记录中很难再发现洪水事件信号,沉积地球化学物源指标趋于稳定。As part of the"sediment source to sink"study,the provenance of sediment in East Asian marginal seas is of great importance,thus making the provenance of Changjiang sediment over different timescales one of the critical research issues.Trace elements and neodymium isotopes were analyzed on a 2.45 m-long sediment core at Chongming Island.Proven provenance indicators widely used to determine the sediment sources from the river catchment,εNd,Eu anomaly(δEu),Cr/Th and Sc/Th displayed distinct variations in the Changjiang catchment between the years1858 and 1906,then became steady between 1906 and 1988.Combined data from previous studies suggested dividing the sediment source into four end-members,rather than upper and middle/lower catchment as previously.The four proposed end-members are(1)the Dongting and Poyang Lakes and their connected tributaries;(2)Han River;(3)Jialing River;and(4)the other tributaries in the upper catchment areas.A linear mixing model was used to quantify the contribution from each of the end-members.The result reveals that the other tributaries in the upper catchment and Hanjiang made a significant sediment contribution between 1858 and 1988,which corresponds well to flood events in 1858-1906.The steady source provenance since 1906 is attributed to anthropogenic changes on Chongming Island:for instance,dam construction,which has averted sediment deposition during the flood season and thus eradicated the provenance discrepancy promoted by the flood events.

关 键 词：长江沉积物来源 洪水事件 崇明岛 物源指标 人类活动 

分 类 号：P512.2[天文地球—地质学]