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长江口泥质区24Z孔沉积物粒度特征及对洪水事件的沉积响应
盛琛
中国地质大学(北京)海洋学院
摘要:
对长江口泥质区24Z孔的沉积物柱状样进行了粒度和元素分析,根据沉积物的粒度特征可将岩芯从下到上分为三个阶段:A阶段(1931至1964年)粒度参数的波动较小,平均粒径波动范围在5.576~7.651φ;B阶段(1964年至1983年)粒度参数波动范围比A阶段更小,整个阶段没有出现明显峰值,平均粒径波动范围在6.511~7.371φ;C阶段(1983至2003年)粒度参数波动范围明显增大,出现多个峰值,平均粒径波动范围在5.591~7.456φ。Zr/Rb值大小实际上反映了粗粒级矿物与粘土粒级矿物的相对含量的高低,24Z孔的沉积物中Zr/Rb值波动范围在1.02~3.59之间,出现了多个明显的峰值。长江洪水灾害是我国频率高、为患严重的自然灾害之一,大洪水期间沉积物的粒度和化学特征往往发生明显改变。利用24Z孔沉积物平均粒径和Zr/Rb比值识别出多个突变层位,结合长江中下游洪水水文记录,发现突变层位年代与八十年代后的水文洪水年份有着较好的对应,这可能与长江主泓的变化有关。对比突变层位与正常层位的粒度特征,突变层位沉积物的粒度频率曲线呈负偏态且峰高而尖,正常层位粒度频率曲线呈正偏态且峰低而宽,同时,概率累积曲线也指示突变层位沉积物在沉积过程中受到了更强的水动力作用。
关键词:  粒度,长江口泥质区,洪水事件,Zr/Rb比值
DOI:10.11759/hykx20190513002
分类号:P736.2
基金项目:中国地质调查“海底地球化学填图试点(DD20190237)”项目资助
Grain-size characteristics of sediments and sedimentary response to flood events from hole 24Z in muddy area of the Yangtze Estuary
Sheng Chen
School of Ocean Science, China University of Geosciences (Beijing)
Abstract:
Grain size and element content were analyzed for sediment columnar sample of 24Z core in argillaceous area of the Yangtze Estuary. According to the grain size characteristics of sediments, the core can be divided into three stages from bottom to top.In stage A (1931-1964), the fluctuation of particle size parameters was small, and the range of average particle size fluctuation ranged from 5.576 to 7.651φ. In stage B (1964-1983), the fluctuation range of particle size parameters is smaller than that in stage A, and there is no obvious peak value in the whole stage. The average fluctuation range of particle size is 6.511-7.371φ. In stage C (1983-2003), the fluctuation range of particle size parameters increased significantly, with multiple peaks. The average fluctuation range of particle size was 5.591-7.456φ. The value of Zr/Rb actually reflects the relative content of coarse-grained minerals and clay-grained minerals. The value of Zr/Rb in 24Z pore sediments fluctuates from 1.02 to 3.59, and there are many obvious peaks.The flood disaster of the Yangtze River is one of the most frequent and serious natural disasters in China. This study is the first attempt to reconstruct flood events at the southern end of the muddy area of the Yangtze Estuary by using the average sediment size and Zr/Rb ratio. Compared with flood hydrological records, the identified flood time has a good record of flood events since the 1980s. This may be related to the change of the main channel of the Yangtze River.Compared with the grain-size characteristics of flood and non-flood layers, the grain-size-frequency curves of flood sediments show negative skewness and peaks are high and sharp, while the grain-size-frequency curves of non-flood layers show positive skewness and low and wide peaks. At the same time, the probability cumulative curves also show that the sediments of flood layers are subjected to stronger hydrodynamic effects in the deposition process.
Key words:  grain size  muddy area of the Yangtze Estuary  flood events  Zr/Rb
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