美国西部红层地貌发育及与中国东南部丹霞地貌的对比

美国西部和中国东南部都是世界上中生代红层的主要分布区,形成了以赤壁丹崖为特征的地貌景观,具有很高的对比研究价值。通过地质资料分析和野外考察,对美国西部红层的分布和形成年代,地质构造背景,岩性和地貌特征等进行梳理,并和中国东南部丹霞地貌进行对比。结果表明：美国西部红层地貌和中国东南部丹霞地貌都是发育在红层基础上的侵蚀地貌,都有显著的红色陡崖坡,但受控于区域地质构造、物质基础、及主导外营力等因素的差异,两地具体的地貌特征并不完全一致。美国西部红层主要形成于三叠纪和侏罗纪,红层堆积的构造环境为大型弧后盆地,沉积环境复杂多变,以陆相为主,尤以风沙沉积最为典型,岩性以细砂—粉砂岩和泥岩为主,砾岩很少,主导外营力为流水下切,红层发育的地貌类型相对单一,总体以高原—峡谷景观为主。中国东南部丹霞地貌区的红层多形成于白垩纪,构造环境为内陆中小型断陷/拗陷盆地,沉积环境全部为陆相,以粗碎屑混杂堆积为主,主导外营力以流水冲刷侧蚀为主,发育的地貌类型较为多样,整体以簇群式峰丛—峰林景观为主。

Development of red bed landform in the western United States and a comparison with Danxia landform in southeast China

The western United States and southeastern China, featured by landscapes of red cliffs, are major distribution regions of red beds in the world. It is of great value to make a comparative study on red beds and landform development in these two regions. Based on geologic literature analysis and field investigation, this study summarizes the distribution, age, geologic background, lithology, and geomorphic features of red beds in the western United States. Then, a comparison with Danxia landform in southeast China was conducted. It reveals that red bed landform in the western United States and Danxia landform in southeast China are erosional landform developed on red beds, with red cliffs as a remarkable geomorphic feature. However, due to differences in regional geologic background, material basis, and the dominant exogenic force, specific geomorphic features in these two areas are not exactly the same. Red beds in the western United States were mainly deposited in a huge back-arc basin during the period from Triassic to Jurassic. Although depositional environment for these red beds are complex, most of them are continental deposits, especially eolian deposit. In terms of lithology, the majority of red beds in the western United States are composed of fine-grained sandstones, siltstones or mudstones, with very few conglomerates. In terms of geomorphic development of red beds in this region, the downcutting process by flowing streams has been playing a dominant role, creating relatively simple red bed landform types that are characterized by a geomorphic combination of plateau and canyons. As for Danxia landform in southeast China, red beds were deposited in Cretaceous in small and medium-sized rift basins or depression basins. They are all continental deposits, mainly composed of coarse-grained clastic rocks. In aspect of landform development, the controlling exogenic factor is lateral erosion by streams, which produces various types of red bed landforms, with peak clusters and hoodoos as overall landscape feature.