中文摘要：

自1855年黄河入海位置由黄海改为渤海以来,尾闾经历了十余次大的改道,最近的两次大的人工改道分别发生于1976年和1996年。研究了取自黄河水下三角洲的两个沉积物岩心,系统开展了沉积物粒度、210 Pb放射性同位素分析。研究表明：两个沉积物岩心垂向上粒度组成出现突变,它们记录了1976、1996年两次黄河入海口的变迁。其中A19站下段（14.0～24.0cm）属于三角洲沉积,上段（0～14.0cm）属于海岸沉积,记录了1996年黄河从清水沟改道清8汊入海的河口变迁;A25站下段（15.5～24.0cm）属于正常海岸环境沉积,上段（0～15.5cm）属于三角洲沉积,记录了1976年黄河从刁口改道清水沟入海的变动。黄河入海口的变动导致该处沉积物岩心中210Pb曲线复杂化,出现了阶段式、倒置式等形态,该曲线形态与黄河入海口的波动相一致。

英文摘要：

Since entered into the Bohai Sea in 1855,the mouth of the Yellow river has shifted for a dozen times.The last two times of artificial diversion were happened in 1976 and 1996respectively.Recently,two sedimentary cores have been taken from the Yellow River Delta,and the grain-size and 210 Pb systematically studied.The grain-size components show dramatic changes when the river mouth migrated in 1976 and 1996.The lower part of core A19（14.0～24cm）was formed in a deltaic environment,while the upper part（0～14.0cm）formed in a coastal environment.The grain size variation at 14.0cm recorded the migration of river mouth in 1996.The lower part（15.5cm～bottom）of core A25 was formed in a coastal environment,while the upper part was formed in a deltaic environment,indicating the mouth migration in1976.The 210-Pb curves were in a periodical or anti-decay pattern,matching well with the river mouth migrations.