黄河兰州段河谷演化研究与认识

Research and Understanding of the Evolution of the Yellow River Valley in Lanzhou

兰州盆地作为黄河自青藏高原流入黄土高原的转折点,其河谷演化对黄河水系在不同地貌单元的演化研究有承上启下的意义。兰州黄河河谷演化研究至今已有近100年的历史,在研究过程中取得了重要的研究成果和认识:①兰州盆地黄河河谷之上发育1级剥蚀面,河谷中发育了宽广连续的9级阶地;利用多种测年技术较系统地测定了1级剥蚀面和9级黄河阶地的年代。②提出兰州黄河基座阶地的形成模式——在长期地面抬升的背景下,气候变化控制阶地形成的年代,抬升速率影响阶地的级数。③兰州至其上游各盆地内黄河最高级阶地年代逐渐年轻化,揭示现代黄河上游水系格局的形成是黄河自兰州盆地不断溯源侵蚀,逐渐贯通上游内流盆地的结果。同时,阶地序列年代学仍需继续深入,区域构造抬升变形特征缺乏直接证据,阶地发育模式需要模型模拟进行验证,水系变化的地貌响应不清楚,以及阶地河漫滩沉积记录的河流过程缺乏关注,这些问题将是今后研究的重点。

As the turning point of the Yellow River flowing from the Tibetan Plateau to the Loess Plateau,the valley evolution of Lanzhou Basin is of great significance to the study of the evolution of the Yellow River system in different geomorphic units.The evolution of the Yellow River Valley in Lanzhou has been studied for nearly 100 years.In the process of research,important research results and understandings have been obtained as follows:①The denudation surface develops above the Yellow River Valley in Lanzhou Basin,and the broad and continuous 9-level terrace develops in the valley.The age of the denudation surface and 9-level Yellow River terrace was systematically determined by using a variety of dating techniques.②The development pattern of the strath terraces of the Yellow River in Lanzhou was put forward.Under the background of long-term ground uplift,climate change controls the age of terrace formation,and the rate of uplift affects the number of terrace.③The age of the highest terrace of the Yellow River in the basins from Lanzhou to the upper reaches of the Yellow River is gradually younger.It is revealed that the formation of the present pattern in the upper reach of the Yellow River is the result of the headward erosion from Lanzhou Basin and the drainage intergration of the internal flow basin.At the same time,the chronology of terrace sequence still needs to be deepened,the characteristics of regional tectonic uplift and deformation are lack of direct evidence,the development pattern of terrace needs to be verified by model simulation,the geomorphic response of drainage change is not clear,and the river process recorded by the deposition of terrace flood plain is lack of attention.All those issues will be the focus of future research.