鄂尔多斯高原黄河支流阶地和裂点研究

The formation and evolution of the Yellow River is an important issue of fluvial landscape and regional geomorphology in China. Many investigations of the landscape evolution of the river have been performed, and mainly focused on the main stream of the river in the upper and middle reaches, especially in the Jinshaan gorge located in the eastern Ordos Plateau (Chinese Loess Plateau). However, relatively little research has been carried out on the tributaries of the Yellow River and to date only a few research groups have focused on this topic. This project is intended to investigate the fluvial terraces and knickpoints in the tributaries of the Yellow River in the Ordos Plateau. The studied rivers include 22 tributaries, such as Weihe, Kuyehe, Wedinghe, Tuweihe and Yanhe. We use DEM to extract parameters such as channel slope and drainage area. In field we identify paleochannel positions (terrace) by looking for the exposures of fluvial gravel and sand, which are usually covered by loess/paleosol sequence in the study region. We observe and measure knickpoints in situ. The elevation of the terrace and knickpoints are measured using differential GPS and other devices. Samples from different sedimentary facies of terrace deposits are systematically dated using optically stimulated luminescence techniques. Terrace sequence and chronology for each tributary will be established. The factors affecting terrace formation and the relationship between the terraces of the tributaries and the Yellow River are investigated. A distribution map of knickpoints in the study area is constructed, and the factors affecting the evolution of knickpoints and the relationship between the knickpoint and the Yellow River are be investigated. The implication of the evolution of the tributaries and knickpoints for the Yellow River and the effect of headward erosion of knickcpoints and the evolution of the Yellow River on the evolution of the Loess Plateau landscape will be discussed.

黄河的形成和演变是中国河流地貌与区域地貌的重大基础理论问题，前人做了大量的研究，这些工作主要集中在黄河中上游地区的干流，尤其是鄂尔多斯高原东部的晋陕峡谷河段。然而黄河支流的研究相对较少。本项目准备对鄂尔多斯高原上发育的渭河、窟野河、无定河、秃尾河和延河等22条黄河支流进行阶地和裂点调查研究。通过DEM分析提取有关流域面积、河床坡度等参数，在野外依据河谷两岸的河流沉积露头确定古河床（阶地）的位置并进行阶地划分和对比，实地观察裂点，用差分GPS等测量阶地和裂点的高程。通过阶地堆积物的系统光释光测年，建立各支流阶地的年代序列并确定其形成的影响因素以及与黄河干流阶地的关系。绘制各支流流域的裂点分布图，分析影响其发育的因素及与黄河演化的关系。探讨黄河支流阶地和裂点的发育演化对黄河演化的指示意义，以及裂点溯源侵蚀和黄河演化对黄土高原地貌的影响。

本项目《鄂尔多斯高原黄河支流阶地和裂点研究》是国家自然科学基金委批准的面上项目（批准号41471003），执行年限2015.01-2018.12）。在执行期间主要开展了以下工作：（1）黄河主要支流阶地与裂点发育特征及其与黄河演化的关系；（2）黄河晋陕峡谷下游段支流下切历史的数学模拟研究；3）黄河支流裂点的识别及其分布规律；（4）晋陕峡谷黑峪口地区黄河阶地形成年代研究；（5）对外开展了其它研究内容的科研合作。取得的主要结果有：（1）通过DEM和谷歌地球影像分析和野外工作，说明了晋陕峡谷各支流的地貌形态特点，鄂尔多斯地块的抬升速率可能大于黄河及支流的下切速率；（2）通过水动力模型的模拟得到了黄河及支流在晚更新世以来的下切速率，在95-75 ka间的下切速率为0.93 mm/a；在75-30 ka间为0.30 mm/a；在30 ka至今为0.54 mm/a，气候或降水对下切速率的大小起了重要作用，推测壶口瀑布在8万年前已经形成，其高度与这期间鄂尔多斯抬升的高度吻合都是约38米；（3）根据距离和坡度图与水力学方程及DEM图对晋陕峡谷下游段（壶口瀑布下游）的支流裂点分析表明，各支流发育的裂点类型相似，距上游源头10 km的河段内没有裂点分布，距黄河5-10 km的支流河段是典型的裂点分布区，推算出晋陕峡谷下游段的黄河至少在2.28 Ma前就已经形成；（4）阶地的光释光年代学研究表明石英的单片再生剂量法是测量本区阶地堆积物年代最可靠的方法，但测量的可靠上限可能不超过10万年，在黑峪口地区识别出7级阶地，22个光释光样品的年龄数据表明黑峪口地区黄河阶地的第二、三和四级基座阶地的形成年代分别约为65、76 和108 ka，第五，六和七级阶地的形成年代大于128 ka。计算的下切速率为0.3 mm/yr（108 ~76 ka）、 2.8 mm/yr (76~69 ka)和0.2 mm/yr (65 ka–现在). 上面这些结果对我们进一步理解黄河的演化具有重要意义。（5）在贵州黔西县观音观发现了东亚最早的具有勒瓦喽哇技术的石器，年代约为80-170 ka。项目在执行期间已发表了9篇标注本项目资助的学术论文，其中有8篇发表在国际学术期刊上。