黄河入海口变迁的沉积记录:来自粒度和210Pb的证据

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、210Pb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。

SEDIMENTARY RECORDS OF THE YELLOW RIVER MOUTH MIGRATION: EVIDENCE FROM GRAIN-SIZE AND210Pb

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 1996 respectively. Recently, two sedimentary cores have been taken from the Yellow River Delta, and the grain-size and 210Pb 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 in 1976. The 210-Pb curves were in a periodical or anti-decay pattern, matching well with the river mouth migrations.