Formation Model Of Danxia Landform In The Longhushan Geopark, China

Danxia landform, characterized by red wall or red cliff, derives from red continental clastic deposits. As a typical Danxia landform-dominated park, the Longhushan Geopark is taken as my working area, the distribution, development conditions and classification of the Danxia landforms are revealed, with the assistance of remote sensing technology and information about the regional geology setting. The first factor concerning the formation of Danxia landform is lithology. The Danxia landform in the park is developed in mainly in the Hekou Formation of Late Cretaceous, secondly in the Tangbian Formation. The landforms developed in the two formations show obviously different topology. The Hekou Formation is a series of coarse clastics in alluvial-fluvial fan at piedmont, dominated by the reddish purple clumpy conglomerate and sandy conglomerate, including some interbeds of coarse-grained sandstone with pebbles, fine-silt sandstone with pebbles and ferric siallitic or calcareous cementations. Conglomerate is stronger against the wind or water erosion than sandstone and silt-sandstone. Such rocks evolved into red wall or cliff, protuberances or concaves (large concaves can further develop into rock tanks or caves), because the rock body collapses along the vertical joints by the gravity not in balance after the softer interbeds are eroded firstly. On the other hand, the Tangbian Formation is in a series of fine-grained clastics in a set of aeolic sand dunes, dominated by the reddish purple clumpy fine sandstone, containing a little fine sandstone with pebbles and thin laminated silt-sandstone. This lithology tends to form dwarf and gentle hills under erosion, with some lower cliffs and red walls, as well as cave groups in different sizes. The other factors controlling the topology of Danxia landform include the gentle occurrence of the strata, and fractures or vertical joint (fissure) structures. The occurrence of strata defines the configurations of the top of rock block and the structured slope. The uplift of the Crust after the deposition of Xinjiang Basin in the Late Cretaceous made an eroded area accompanied with fractures, joint structures, and cross-cuttings of joints and differential uplifts of blocks. The EW and NW-oriented fractures determine the scale, strike and profile of Danxia blocks. The dense NNE-oriented, NEE-oriented and NW-oriented joints define the arrangement pattern of mesas, peak clusters, hoodoos, stone walls, girdles, peaks and columns. The structural uplifts also play an important role in the formation of Danxia landforms. The rapid uplifting area usually develops a series of mesas, peak clusters or hoodoos, whereas relatively slow uplifting area usually has peaks, deep-cutting rivers or valleys. In a word, the external geological drivers to form Danxia Landform are water current erosion (from rain and river) and flow erosion, and collapse by gravity.The landforms in the study area can be divided into three stages. If it is based on the development stages, there is young Stage, Mature Stage and old Stage. It could be distinguished into five types Danxia Landform. From the point view of geological processes and formation ways, they are Current Wash-Offs, Post-Collapse Remainders, Post-Collapse Piles, Water Erosions and Erosion-Collapses. Based on the general topology, there are positive and negative landforms, which can be subdivided into 23 subtypes.