Stepped Landform In Zhangjiajie, Hunan Province

Zhangjiajie, well-known for its spectacular sandstone landforms peaks, has been the subject of geomorphologists and geologists for decades. Prior to our present study, however, little is known about evolutionary and the timing of these spectacular sandstone landforms. Stepped landforms such as alluvial terraces, planation surface and karst caves are well developed in the study area. These can provide important evidence of the geomorphic evolution of the study area. Based on the previous studies, the correlations of the different stepped landforms and geomorphic evolution of Zhangjiajie were detailed analysed by the aid of sedimentology, geomorphology and chronology techniques, providing important information in terms of regional climate changes and tectonic movements.Field investigations indicate the occurrences of one planation surface and one erosion surface in the study area. The planation surface is at the evlevation of 1100 to 1300m, above which typical weathering crust and various karst landscapes appeared. The well-preserved sandstone platform under the planation surface form erosional surface, with an average elevation of 800 to 950m.The planation surface occurred in Late Tertiary and erosional surface formed in the Early Pleistocene.Fluvial terrace levels and karst caves were well preserved along the rivers in Zhangjiajie. Electronic spin resonance (ESR) method and thermal luminescence (TL) method indicated that all the terrace sequences began to aggradate since late Early Pleistocene. The terraces of Zhangjiajie should be the product of tectonic movement and climate change. The tectonic uplift provides a slice of space for aggradation of terraces, and the major effect of climate change is controlling the process of rivers'aggradation and incision.Our results indicate that seven terrace levels, adjusted by the middle Yangtze River network, started to developed in the Maoxi river in 1 Ma. Three terrace levels are well presented in the Suoxi River, with terrace level T4 locally emerging in the middle Suoxi catchment. Huanglong Cave, a typical karst cave in the study area, can be divided into four vertical levels, with the gravel layer occurring in the topmost level. Sedimentological analysis indicates an allochthonous source for the gravels, which have been formed under a warm and humid environment in Mid-Pleistocene. Four primary geomorphic levels are distinctive in the Zhangjiajie sandstone landforms, displaying a good geomorphic correlation with the alluvial terraces and Huanglong Cave in the middle-lower reaches of the Suoxi River. We thus can infer the timing of sandstone landforms formation in Zhangjiajie at Mid-Pleistocene.