盛琛^1,2, 陈彬^2,3, 安郁辉⁴, 张欣^5,6, 陈立雷², 刘健^2,3
1.中国地质大学(北京)海洋学院, 北京 100089;2.中国地质调查局青岛海洋地质研究所, 山东 青岛 266071;3.青岛海洋科学与技术试点国家实验室海洋矿产资源评价与探测技术功能实验室, 山东 青岛 266071;4.山东科技大学 地球科学与工程学院, 山东 青岛 266590;5.中国地质大学(武汉)地球科学学院, 湖北 武汉 430074;6.中国地质科学院, 北京 100032

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3个阶段：A阶段（1931-1964年）粒度参数的波动较小，各层位平均粒度Φ在5.58~7.65；B阶段（1964-1983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，Φ在6.51~7.37；C阶段（1983-2003年）粒度参数波动范围明显增大，出现多个峰值，Φ在5.59~7.46。元素Zr和Rb质量比（m_Zr/m_Rb）的大小实际上反映了粗粒级矿物与黏土粒级矿物的相对含量的高低，24Z孔的沉积物中m_Zr/m_Rb波动范围在1.02~3.59，出现了多个明显的峰值。利用24Z孔沉积物平均粒度和m_Zr/m_Rb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20世纪80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。研究长江口泥质区南部24Z孔的沉积物粒度特征和对洪水事件的沉积响应，可以更好地了解长江洪水所携带的粗颗粒物质在长江口泥质区的分布范围，有助于重建长江流域古洪水从而更好的认识长江流域洪水发生的规律。
关键词:粒度长江口泥质区洪水事件Zr和Rb质量比(m_Zr/m_Rb)
DOI：10.11759/hykx20190513002
分类号:P736.2
基金项目:中国地质调查资助项目（DD20190237）；青岛海洋科学与技术试点国家实验室鳌山科技创新计划项目（2016ASK13）

Grain-size characteristics of sediments and sedimentary response to flood events from hole 24Z in muddy areas of the Yangtze Estuary
SHENG Chen^1,2, CHEN Bin^2,3, AN Yu-hui⁴, ZHANG Xin^5,6, CHEN Li-lei², LIU Jian^2,3
1.School of Ocean Science, China University of Geosciences(Beijing), Beijing 100089, China;2.Qingdao Institute of Marine Geology, China Geological Survey, Qingdao 266071, China;3.Laboratory for Marine Mineral Resources, Pilot National Laboratory for Marine Science and Technology(Qingdao), Qingdao 266071, China;4.College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China;5.Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China;6.Chinese Academy of Geological Sciences, Beijing 100032, China
Abstract:
In this study, grain size and element content were analyzed in a columnar sediment sample of a hole 24Z core in an argillaceous area of the Yangtze Estuary. According to the grain size characteristics of the sediments, the core can be divided into three stages from bottom to top. In stage A (1931-1964), the fluctuation in the particle size was small, and the range in the average-particle-size (Φ) fluctuation ranged from 5.58 to 7.65. In stage B (1964-1983), the fluctuation range of particle size was smaller than that in stage A, there was no obvious peak value in the whole stage, and the Φ fluctuation ranged from 6.51 to 7.37. In stage C (1983-2003), the fluctuation range of the particle size increased significantly, showed multiple peaks, and the Φ fluctuation ranged from 5.59 to 7.46. The mass ratio of elements Zr and Rb (m_Zr/m_Rb) actually reflected the relative content of coarse-grained and clay-grained minerals. The value of m_Zr/m_Rb in the 24Z pore sediments fluctuated from 1.02 to 3.59, and had many obvious peaks. Flood disasters due to the Yangtze River are some of the most frequent and serious natural disasters in China. This study represents the first attempt to reconstruct flood events at the southern end of the muddy area of the Yangtze Estuary based on the average sediment size and m_Zr/m_Rb. Compared with hydrological flood records, the timing of identified flood events have been well recorded since the 1980s. This may be related to the change in the main channel of the Yangtze River. A comparison of the grain-size characteristics of flood and non-flood layers shows that the grain-size-frequency curves of flood sediments are characterized by negative skewness with high and sharp peaks, whereas the grain-size-frequency curves of non-flood layers show positive skewness and low and wide peaks. The cumulative probability curves also show that the sediments of flood layers have been subjected to stronger hydrodynamic effects during the deposition process.
Key words:grain sizemuddy area of the Yangtze Estuaryflood eventsmass ratio of elements Zr and Rb (m_Zr/m_Rb)





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