【作者】 胡刚；

【导师】 李安春；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋地质学， 2014， 博士

【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。更多还原

【Abstract】 A great amount of terrigenous sediment coming from the Changjiang river basinhas formed a magnitude subaqueous delta. The researches on sedimentary evolutionof the subaqueous delta are important to explaining the land-ocean interaction. Forhigh sedimentation rate and its continuous and relative stable sedimentation, theresearches on the mud area of Changjiang delta has special advantages in revealingthe high resolution sedimentation and environment during the past century. Based onthe actual measurement data and samples from the offshore area, we discuss themodern sediment environment and changes in climate and environment during the last120a by the methods of grainsize analysis, clay mineral analysis and geochemicalanalysis.Based on in-situ measurements, we found that the current velocity has obvioustidal cycle variation and unconspicuous annual variation. The variation of suspendedsediment concentration relies on the hydrodynamic and there are2-4times peakvalues in concentration during a tidal period in general. For space distribution pattern,the hydrodynamics and suspended sediment concentration decrease from theChangjiang estuary to the north-east direction and sharply decease at123°E which isalmost the east boundary of the Changjiang diluted water. By the aid of DigitalElevation Model, the sediment discharge transported to the offshore area hasdecreased in the past20a and the geomorphology has been eroded. The influence ofhuman activities, dam construction and conservation of water and soil included, resultin the sharply decrease of sediment transport.There are3main types of surface sediment in the research area, including silt,silty sand and sandy silt. The data indicate that the provenance of sediment is mainly influenced by the Changjiang sediment. On the other hand, the Huanghe sediment hasa limited effect on the surface sediment distribution and its influence becomesincreasing from the estuary to the north-east.We have finished experiment tests about the core CJ0702. And the resultsindicate that the sedimentation environment within mud area is in stable conditionduring the last120a with average sedimentation rate3.11cm/a. The parametervariations, including grain-size, clay mineral and chemical elements, appear smallerchanges and fluctuating vertically. The provenance analysis proves that the sedimentconsisting of CJ0702core is mainly controlled by the Changjiang sediment andinfluenced by the Huanghe sediment jointly. According the vertical variation ofchemical elements, the sediment from the Huanghe River presents an increasing trendwithin the past century.A spectrum analysis was made for the variations of grain-size and chemicalwreathing index in core CJ0702. There are two types of periodic variation,2-8a and16-20a, observed in these two parameters within the core. These two periodicvariations have good correspondence with the ENSO and PDO respectively. Based onthe sensitive grain size combining with the Zr/Rb value and magnetic susceptibility,the flood events happening in the Changjiang river basin have great influence withsedimentation in the mud area and there are about20times flood events distinguishedfrom the sedimentation records. Despite of natural environment factors, the humanactivities, including major construction projects on the Changjiang river basin andsome other economic activities, have great impact on the sedimentation in researcharea equally.更多还原