近百年来长江口滨外区沉积作用及其对环境变化的响应

发布时间：2018-11-03 16:05

【摘要】：长江流域带来丰富的陆源碎屑沉积物，在河口及浅海陆架区形成了庞大的河口三角洲，三角洲的沉积演化过程研究对揭示陆海相互作用具有重要意义。长江口外泥质区沉积速率较高，具有相对稳定、连续的沉积作用，对于揭示近百年来该地区高分辨率的沉积作用和沉积过程具有独特的优越性。本研究以长江口滨外区现代沉积环境实测资料，结合CJ0702柱状样品为研究对象，通过多种实验测试手段，包括粒度分析、黏土矿物分析、地球化学分析等，讨论现代长江口滨外区沉积环境及地貌变化特征，并揭示近百年来研究区气候与环境的变化过程。通过对定点站位连续三年动力观测和滨外区大面站观测的资料分析，表明长江口滨外区流速具有明显的潮周期变化，年际变化不大，与之对应的悬沙含量变化与动力变化关系密切，在一个潮周期内常出现2-4次不等的泥沙峰值，且年际变化也较小。长江口外地区沉积动力和悬沙含量平面分布特征，由口门外向东向北逐渐降低，以123°E为界出现明显的变化，该界限几乎是长江冲淡水的影响的东界。近二十年来长江口滨外区冲淤计算表明，长江口滨外区泥沙落淤总量出现减少趋势，水下地貌开始受到侵蚀。受三峡大坝建设的影响，，该地区泥沙落淤总量出现明显降低，在大坝运行相对平稳后出现缓慢增长。研究区表层沉积物类型以粉砂、粉砂质砂和砂质粉砂为主，通过表层沉积物粒度变化、矿物分析和元素地球化学分析，表明研究区主要受到长江沉积物的影响，但是向东北方向黄河沉积物的影响逐渐增强。通过对CJ0702柱多要素指标的分析，表明该地区近120年来沉积环境比较稳定，沉积速率能够达到近3.11cm/a，不管是岩心沉积物粒度、矿物还是化学成分，在垂向上变化幅度较小，呈现波动性变化。通过物源分析，CJ0702柱物质来源主要受长江源物质控制，但受到黄河物质的一定影响，且近百年来影响程度有一定的增加趋势。通过谱分析方法研究表明，近百年来该地区粒度及化学风化指数呈现周期性变化趋势，都存在2-8a和16-20a不等的周期性变化趋势，与PDO年代际周期变化及ENSO年际周期变化具有良好的对应关系。通过敏感粒度组分分析，结合Zr/Rb值和岩心磁化率，研究近百年来长江流域洪水事件在沉积记录中的响应，在沉积记录中识别了近二十几次大洪水。通过沉积物粒度变化及地球化学元素含量变化，同时表明对流域重大工程建设和人类经济活动，在沉积记录中同样有所反应。
[Abstract]:The Yangtze River basin brings abundant continental clastic sediments and forms a huge estuarine delta in estuaries and shallow continental shelf areas. The study on the sedimentary evolution process of delta is of great significance to reveal the interaction between land and sea. The depositional rate of the muddy area outside the Changjiang Estuary is relatively high, with relatively stable and continuous sedimentation, which has unique advantages in revealing the high-resolution deposition and the deposition process in this area in the last hundred years. In this study, the measured data of modern sedimentary environment in the offshore area of the Yangtze River Estuary, combined with CJ0702 columnar samples, were studied by various experimental means, including particle size analysis, clay mineral analysis, geochemical analysis, etc. The characteristics of sedimentary environment and geomorphologic change in the offshore area of the Yangtze River Estuary are discussed, and the process of climate and environment change in the study area in the last hundred years is revealed. Through the analysis of the data of dynamic observation at fixed point station for three consecutive years and observation of large surface station in the offshore area, it is shown that the velocity of velocity in the offshore area of the Yangtze River Estuary has obvious tidal cycle variation, but the interannual variation is not obvious. The change of suspended sediment content is closely related to the dynamic change, and the peak value of sediment varies 2-4 times in a tidal cycle, and the interannual variation is relatively small. The sedimentary dynamics and suspended sediment content in the area outside the Yangtze River Estuary gradually decreased from the entrance to the east to the north, with 123 掳E as the boundary, which is almost the eastern boundary of the Yangtze River diluted water. The calculation of scour and siltation in the offshore area of the Yangtze River Estuary in the past two decades shows that the total sediment deposition in the offshore area of the Yangtze River Estuary is decreasing and the underwater geomorphology is beginning to be eroded. Under the influence of the construction of the three Gorges Dam, the total sediment deposition in this area is obviously reduced, and the slow increase occurs after the relatively stable operation of the dam. The main types of surface sediments in the study area are silt, silty sand and sandy silt. Through the grain size change of surface sediment, mineral analysis and element geochemistry analysis, it is shown that the study area is mainly affected by Yangtze River sediments. However, the influence of the Yellow River sediment toward the northeast is increasing gradually. Based on the analysis of the multi-element indexes of CJ0702 column, it is shown that the sedimentary environment in this area is relatively stable in the last 120 years, and the deposition rate can reach 3.11 cm / a, regardless of the grain size, mineral or chemical composition of the core sediment. In the vertical change range is small, showing volatility changes. Through provenance analysis, the material source of CJ0702 column is mainly controlled by the source material of the Yangtze River, but it is influenced by the material of the Yellow River to a certain extent, and the influence degree has a certain increasing trend in the last hundred years. The results of spectral analysis show that the grain size and chemical weathering index of the region have a periodic variation trend in the past hundred years, and there are periodic trends ranging from 2-8 years to 16-20 years. It has a good correspondence with PDO Interdecadal cycle change and ENSO interannual cycle change. The response of flood events in the Yangtze River basin to sedimentary records in the last hundred years has been studied by means of the analysis of sensitive particle size components, combined with Zr/Rb value and core magnetic susceptibility. More than 20 major floods have been identified in the sedimentary records. The variation of sediment grain size and the content of geochemical elements also indicate that the sediment records are also responsive to the major project construction and human economic activities in the basin.
【学位授予单位】：中国科学院研究生院（海洋研究所）
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P736.21

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