放射性同位素定年技术在崇明岛潮滩沉积速率上的应用研究

选取崇明岛北侧由东至西4个潮滩沉积柱,分析137Cs、226Ra和210Pb放射性比活度,应用210Pb和137Cs放射性同位素定年方法计算崇明岛潮滩沉积物沉积速率。对于东西两端,210Pb方法测得速率分别为3.08cm/a和2.34 cm/a,而137Cs测得速率分别为6.19 cm/a和2.06 cm/a。结果表明,137Cs定年方法计算出的潮滩沉积速率普遍大于210Pb方法结果;但两者反映了相同的速率规律。崇明岛主力生长方向为东和东北,西侧沉积作用相对较弱,表现出"东快西慢"的特点。沉积纵向上,1954年以来,自下而上沉积速率逐渐减缓。

Application of Radioisotope Geochronology in Study on Sedimentation Rate of Tidal Flat of Chongming Island

Four tidal flat sediment cores were collected from east to west along the northern shore of Chongming Island and specific activities of ¹³⁷Cs, ²²⁶Ra and ²¹⁰Pb were determined. The sedimentation rates of the Chongming Island mudflats were calculated by means of ²¹⁰Pb and ¹³⁷Cs geochronology. For the east and west ends of the northern mudflats, the sedimentation rates by ²¹⁰Pb geochronology were 3.08 cm/a and 2.34 cm/a respectively, while the sedimentation rates by ¹³⁷Cs geochronology were 6.19 cm/a and 2.06 cm/a respectively. Although the sedimentation rates calculated by ¹³⁷Cs are generally higher than those from ²¹⁰Pb, the same feature of sedimentation rates, viz "faster in the east, slower in the west" was indicated. And vertically the sedimentation rates were gradually slowdown from the bottom to the top since 1954.