堰塞坝、湖及溃坝堆积的地貌过程与沉积特征的综合研究

The Quaternary barrier dams belong to one of the important morphologic type in mountainous area, which have impressive influences on the change of mountainous environment. To ascertain the landform processes and sedimentary features of the barrier dams, lakes and outburst deposits, it is very important for the knowing of the geologic processes of mountainous hazards and reconstruction of the palaeogeography. In the same time, the project fills a lacuna in the research on diamicton accumulation, because both at home and abroad what lacks is the systematic knowing of the characteristics of sedimentary facies for the outburst deposits. The upper Jinsha River is located in the southeastern edge of the Tibetan Plateau, where the neotectonic movement is very active and the ancient and modern barrier dams are well developed. In this project, the major study objects are the barrier dams, lakes and outburst sediments in the upper Jinsha River and its adjacent region. By carrying out geological and geomorphologic survey and analyzing on the remote sensing images, to ascertain the landform shape, sedimentary structure and distribution characteristics of the barrier dams,lakes and outburst sediments. Through systematically analyzing on the lithofacies, partical size, sedimentary structure, gravel fabric and microstructure, to discuss the facies type and model of the outburst sediments. By using Optically stimulated luminescence dating and radiocarbon dating to obtain the high precision age data and establish the formation times and processes of the barrier dams,lakes and outburst sediment. Thus, it could provide theory basis for studying on the development, evolution and hazard risk assessment of barrier dams.

第四纪堰塞坝是山地一种重要的地貌类型，深刻地影响着山地环境的变化。查明堰塞坝、湖及溃坝堆积的地貌过程与沉积特征，对于认识山地灾害地质过程以及古地理重建具有重要的研究价值，同时也填补了混杂堆积研究中的一个空白，因为迄今在国内外均缺乏对堰塞坝溃坝堆积相的系统认识。金沙江上游地处青藏高原东南缘，新构造运动活跃，是古、今堰塞坝的多发地区。本项目以金沙江上游及邻区的堰塞坝、湖及溃坝堆积为研究对象，系统开展野外地质地貌调查，结合遥感图像分析，查明堰塞坝、湖及溃坝堆积体的地貌形态、沉积结构与分布特征。选择典型剖面的岩相、粒度、沉积构造、砾石组构和微结构等进行综合分析，探讨溃坝堆积的沉积相类型与模式。采用光释光和碳十四测年技术获取高精度的年代数据，揭示堰塞坝、湖及溃坝堆积的形成时代与过程，进而为堰塞坝的发育演化规律及灾害风险评估研究提供理论依据。

青藏高原东南缘第四纪堰塞坝广泛发育，深刻地影响着该区山地环境的变化。查明堰塞坝、湖及溃坝堆积的地貌过程与沉积特征，对于认识山地灾害地质过程以及古地理重建具有重要的研究价值。本项目以岷江上游和金沙江上游典型堰塞坝、湖及溃坝堆积为研究对象，详细开展了野外地质地貌调查，查明了叠溪和雪隆囊古堰塞坝、湖及溃坝堆积体的地貌形态、沉积结构与分布特征，分析了堰塞湖沉积和溃坝堆积的沉积相类型与沉积特征。采用光释光和碳十四测年技术获取高精度年代数据，揭示了堰塞坝、湖及溃坝堆积的形成年代与演化过程。堰塞湖沉积按其粒度特征可以分为上游段，中游段和下游段三个部分。上游段的沉积物主要是粉砂质砂和砂质粉砂，中游和下游段的沉积物较细，主要是黏土质粉砂和粉砂。堰塞湖溃坝堆积体的沉积相划分为两个大类：巨砾层相、砾石层相和砂层相。每个巨砾层相代表一个高流态沉积事件，而砾石层相和砂层相则是由脉动流沉积形成。微观结构上，堰塞湖溃口位置石英砂的主要表面特征表现为断块结构，中段表现为贝壳装断口以及撞击坑，下段的v型坑等痕迹变得更加明显。这种变化表现了石英砂颗粒之间的碰撞从不均匀的高能碰撞向均匀的低能碰撞转变。采用洪水动力学理论中的水流能量法重建了叠溪古堰塞湖和雪隆囊古堰塞湖的溃决洪水的洪峰流量，其最大洪峰流量分别为49821m3/s和10786m3/s。该项目成果为堰塞湖系统的发育演化规律研究及重大灾害风险评估提供了理论基础。