红层盆地岩性差异对丹霞地貌发育的控制

Lithologic Control on the Development of Danxia Landscapes in Red Basins

陆相红层盆地的岩性在横向上和纵向上都有比较明显的变化,导致发育的丹霞地貌形态迥异。本文以赣东北信江盆地、粤北丹霞盆地、陕北地区为例,采用对比分析、数值模拟等研究手段,总结了红层盆地中常见的岩石及地貌类型,提出岩性在丹霞地貌坡面演化过程中的关键作用。在信江盆地中,龙虎山、龟峰等挺拔高耸的山峰主要发育在盆地南缘的河口组厚层砾岩中,而盆地中部贵溪、弋阳地区的近圆形山丘则产在塘边组大型交错层理风成砂岩中;与其类似,丹霞山的赤壁陡崖主要发育在丹霞组厚层砾岩夹风成砂岩中;相反,陕北地区波浪状地貌主要发育在洛河组风成砂岩中。利用河道-山坡综合地形演化(CHILD)地貌模拟软件,假设在同样的构造抬升和河流侵蚀作用下,分别模拟了细砂岩、细砾岩、中砾岩构成的山体坡面的演化过程。模拟结果显示,细砂岩山体易形成较为平缓的坡面,中砾岩易形成陡峻崖壁和巷谷,而介于二者之间的细砾岩则形成较为明显的沟壑系统。CHILD模拟结果与实地观测一致。因此,红层岩性差异在丹霞地貌演化过程中扮演了重要的角色,也是未来地貌定量模拟研究中需要考虑的关键因素。

The terrestrial red basins are characterized by distinct lateral and vertical lithologic changes, which leads to development of different Danxia landscapes. The comparative analysis and numerical modeling are used to summarize the dominant rock and Danxia landscape types, and to propose that lithology plays a key role in the Danxia slope evolution in the Xinjiang Basin of northeastern Jiangxi Province, Danxia Basin of northern Guangdong Province and northern Shaanxi Province. In the Xinjiang Basin, the prominent cliffs particularly occur in the conglomerate-dominated Hekou Formation at the southern basin margin, while the subrounded low hilly terrains develop in the eolian sandstone-dominated Tangbian Formation in Guixi and Yiyang areas at the middle areas of the basin. Similarly, the prominent cliffs generally occur in the conglomerates with eolian sandstone interbeds of the Danxia Formation in the Danxiashan Global Geopark of northern Guangdong Province. In contrast, the wavy landscapes develop in the Luohe Formation eolian sandstones in northern Shaanxi Province. Under the assumption of the similar tectonic uplift and river erosion, the Channel-Hillslope Integrated Landscape Development (CHILD) model was used to test slope evolution in the fine-grained sandstone, fine-grained conglomerate, and pebbly conglomerate. The modelling results showed that the gentle slopes develop in the fine-grained sandstones, the gullies occur in the fine-grained conglomerates, while the prominent cliffs occurred particularly in the pebbly conglomerates. Therefore, lithology is the fundamental factor that needs to be paid more attention in the future quantitative modeling of Danxia landscapes.