苏北辐射沙洲近岸潮滩沉积环境及其物源示踪研究

The radial sand ridges is a special sedimentary geomorphic unit in the shallow inner shelf of China, and its has unique characteristic due to sand ridge and tidal channel distribution in the world. The sand ridges located on the central coast of Jiangsu province between the Yangtze River delta and the old Yellow River delta, with complex hydrodynamic condition, the development of coastal tidal flat and frequent human activities. At present, The sediment transport has undergone significant, and caused the redistribution and adjustment of sediment in the region due to the reduction of sediment source, human reclamation in coastal tidal flat and tidal channel oscillation since the Yellow River flows northward in 1855. Thus, the coastal tidal flat of radial sand ridges as the research object in this study, to analyzed that the modern sdimentation rates of tidal flat, and reveled that the sedimentary characteristics of sediment under the influence of natural and human activities and investigated that the provenance change of sediment in the coastal tidal flat based on radioactive isotopic dating (210Pb and 239+240Pu), sediment grain size and multi-parameter tracer (trace elements, rare earth elements) methods. This study helps to further understand the dynamic mechanism, sediment transport and morphological evolution in the radial sand ridges, and it is of great significance to the utilization of tidal flat resources, the protectin of coastal wetlands and the stability of shore beach. At the same time, it can also provid a scientific basis for understanding the high resolution research of the sediment environment in the tidal flat.

苏北辐射沙洲是我国浅海内陆架一种独特的沉积地貌单元，因其辐射状沙脊和潮流水道分布而独具世界特色。辐射沙洲位于长江三角洲和古黄河三角洲之间的江苏中部海岸，水动力复杂，近岸潮滩发育，人类活动频繁。1855年黄河北归后，受泥沙来源减少、近岸潮滩围垦、潮汐水道摆动等因素的影响，导致物质输运发生显著变化，引起了区域泥沙重新分配、潮滩沉积环境变化和地貌动态演变。本项目以苏北辐射沙洲近岸潮滩为研究对象，利用放射性同位素测年定量估算潮滩沉积速率，建立年代序列；通过沉积物粒度参数和地化元素指标，探究潮滩近百年来沉积环境特征及其变化过程；结合多指标物源示踪法判定沉积物质来源及各物源的贡献。本研究有助于进一步理解辐射沙洲动力机制、物质输运规律和地貌演变动态，对潮滩资源利用、滨海湿地保护和维护岸滩稳定具有重要的意义，为认识辐射沙洲潮滩沉积环境的高分辨率研究提供科学依据。

苏北辐射沙洲海岸潮滩作为陆海相互作用过渡地带，由于其位置的特殊性与营力的多样性以及先天结构的易变性和敏感性，地貌动态变化剧烈且复杂。针对海岸潮滩的围垦引起的潮滩动力格局调整对岸滩地貌动态产生累积效应，引起的不同时间尺度潮滩地貌格局变化、沉积环境特征及物源变化尚不明确。本研究项目基于多时相遥感影像，研究潮滩地貌演化动态；结合沉积物沉积速率、粒度参数揭示海岸潮滩沉积特征及其环境指示意义；运用黏土矿物和地化元素等指标，判定潮滩沉积物的物质来源。主要得出以下结论：（1）1980-2017年苏北辐射沙洲岸滩地貌冲淤动态变化复杂，主要表现为北翼区地形侵蚀明显，平均侵蚀幅度为47.6m/yr；内缘区北部发生侵蚀，但整体向海淤积，平均向海推进约2-18km；外部沙洲区北部、西北部侵蚀较为严重，整体呈向南移动趋势；南翼区呈淤积和侵蚀交替变化。（2）潮滩沉积物组分主要由粉砂、砂和黏土组成；在空间上，岩芯沉积物自北向南粉砂和黏土含量逐渐减少，砂含量逐渐增加，平均粒径变粗，沉积物呈现由北向南粗化的现象。百年来辐射沙洲潮滩沉积物沉积速率呈减少趋势，潮滩平均沉积速率存在差异且没有明显的变化规律。（3）元素比是反映沉积物来源的一种很好的手段，选取了Mg、Al、Fe、Zn、Rb、Co、Ni等主微量元素的比值来分析沉积物的潜在物源区，最终确定沉积物的潜在物源区为废黄河三角洲和长江。使用Inverse model定量估计沉积物来源，发现废黄河和长江的平均沉积物贡献分别为67.4%和32.6%。（4）苏北辐射沙洲岸滩及其近海沉积物黏土矿物指示在废黄河三角洲潮滩及其相邻海域，以及辐射沙洲北翼潮滩黄河物质占主导，而在长江口附近长江流域物质占主导。本研究有助于进一步理解辐射沙洲动力机制、物质输运规律和地貌演变动态，对潮滩资源利用、滨海湿地保护和维护岸滩稳定具有重要的意义。