川北旺苍苍王峡龙潭子河壶穴形态及成因初探

A preliminary study on the morphology and genesis of potholes in Longtanzi River,Cangwang Gorge,Wangcang,northern Sichuan

河成壶穴是山区河床基岩上常见的微地貌类型,记录了区域地貌演化过程、水流与河床边界相互作用的关键信息。基于此,笔者等以川北旺苍苍王峡龙潭子河110处河成壶穴为研究对象,详细测量其形态特征并进行统计分析。结果表明:非串珠状壶穴大小、深度及形态在河床纵剖面上的分布没有明显的规律性,而串珠状壶穴具有一定的规律性;壶穴集中分布在下寒武统阎王碥组硅质砾岩中,其中发育的石英砂岩夹层对壶穴的形成和演化起到了关键性作用,双层天生桥壶穴则是典型的代表;区内发育NE、E—W向平面共轭X型构造节理和S—N向构造节理,三角形、菱形、不规则形壶穴多受两组或3组节理控制,其中S—N向构造节理还控制了壶穴的长轴走向和河谷走向;构造节理对壶穴口形态的演化影响显著,而对壶穴垂直剖面形态的影响不显著。本研究将丰富和完善河成壶穴地貌的数据资料,为米仓山地区河流地貌和构造演化提供科学依据。

Stream pothole, is a common microrelief type of river bedrock in mountainous area, recording key information of the evolution of regional geomorphy and the interaction between running water and riverbed boundary. In this paper, the morphological characteristics of 110 stream potholes in Longtanzi River, Cangwang Gorge, Wangcang, northern Sichuan, are measured and analyzed statistically. The results show that the size, depth and morphology of common potholes are irregular in the riverbed profile, while bead-like potholes are regular to some extent. The potholes distribute intensively in siliceous conglomerate of the Lower Cambrian Yanwangbian Formation, among which the quartz sandstone interlayers are very important to the formation and evolution of potholes, and potholes in the double-layer natural bridge are the typical representative. NE and E—W planar X-conjugate structural joints and S—N structural joints were developed in the region. Triangular, rhombic and irregular potholes were mostly controlled by two or three sets of joints, among which the S—N structural joints also controlled the long axis direction of the potholes and valley direction. The structural joints have played an important role in the evolution of the mouth morphology of potholes, but have no obvious effect on the vertical morphology of potholes. This study will enrich and improve the research data of stream potholes, provide a scientific basis for the evolution of river geomorphology and tectonics in Micangshan area.