黄河口水下三角洲刁口叶瓣的核素分布与沉积特征

Nuclides distribution and sedimentary characteristics of the Diaokou course in Yellow River subaqueous delta

  • 摘要: 于黄河水下三角洲刁口叶瓣东侧获取柱状样K2,对其进行137Cs活度分析,发现活度剖面在2.7和1.9 m处分别存在一个最大蓄积峰和次级蓄积峰,根据137Cs的大气沉降规律并结合沉积物粒度数据与黄河输沙量,确定其最大蓄积峰对应于1964年,次级蓄积峰对应于1967年。柱状样的粒度组分以深度2.1 m为界可明显划分为两段,下段沉积物粒度组分稳定,上段砂粒含量明显增大并在1.9 m处达最大值。对柱状样210Pbex的活度剖面分析表明,其呈现两段式分布:1.9~3.5 m为衰变层,0~1.9 m为混合层。分析结果表明137Cs活度剖面的蓄积峰、沉积物粒度组分的改变以及210Pbex活度的两段式分布均记录了黄河入海口的变迁,并与黄河入海泥沙量存在对应关系。本文统计了研究区1958—2014年的历史水深资料,分析得出钻孔所处海域在1964—1976年(刁口流路行河期)的淤积厚度远大于1976—2014年(清水沟流路行河期)的侵蚀厚度,因此柱状样K2的137Cs活度剖面的1964年最大蓄积峰与210Pbex活度衰变层得以存在。

     

    Abstract: The columnar sample K2 was obtained from the east side of the Diaokou course of the Yellow River subaqueous delta. By 137Cs activity measurement, it is found that there is a maximum accumulation peak at 2.7 m and a secondary accumulation peak at 1.9 m from the top respectively. After analyzing the atmospheric sedimentation rate of 137Cs, the grain size of sediments and the sediment load of the Yellow River, we infer that the maximum accumulation peak corresponds to the year of 1964, and the secondary accumulation peak to the year of 1967. According to the grain-size distribution, the K2 can be subdivided into two sections above and below the boundary of 2.1 m. the grain-size component of the lower section is rather stable, while the sand content in the upper section keeps increasing and reaches the maximum at 1.9 m. The 210Pbex activity profile exhibits a two-stage distribution pattern as well, 1.9m~3.5m is the decay layer, 0~1.9 m is the mixed layer. The accumulation peak of 137Cs activity profile, the change of sediment grain size components and the two-stage distribution of 210Pbex activity all record the mouth migration of the Yellow River. The sediment discharge of the Yellow River also plays an important role in the distribution of nuclides and sediment grain size. Based on the historical bathymetric data of the study area collected from 1958 to 2014, we could conclude that the deposited thickness of research area during the period from 1964 to 1976 (Diaokou River Passage) is much larger than the eroded thickness from 1976 to 2014 (Qingshuigou River Passage).

     

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