Development Conditions of Karst Platform - Canyon
(1) Widespread carbonatite constitutes the basic condition for the forming of karst platform-canyon.
In the geopark, carbonatite formation has been developed widely, including slope platform facies carbonate intercalated with argillaceous sediments in the Cambrian system and Ordovician system, as well as neritic facies carbonate intercalated with siliceous sediments in the Permian system and Triassic system. The sediment up to a thousand meters deep covers an area of about 2100.32km2, representing 73.41% of the total area of the geopark. As the carbonate minerals in the rocks are readily soluble in water while the pores between the silt, arenite and psephite contained in the rocks are of easy enrichment of water, such impure carbonatite containing mud and silt is weak in resisting weathering and corrosion, among the worst in various kinds of carbonatite. Under them are Shipai formation in Cambrian system and Silurian strata consisting of silty shale, argillite and argillaceous siltstone, which are of poor water permeability. They are often formed the base of platform-canyon zone but experienced no further corrosion.
(2) Special geological structure plays an important role in the formation of platform-canyon karst landform
The geopark is located by chance among three primary fractures , i.e., Zhangjiajie-huayuan Fracture, Malichang Fracture and Guzhang-Jishou Fracture, thus being a relatively separate landform unit where the widely developed secondary and tertiary fractures as well as high-angle joints and fissures were beneficial for the formation of karst canyons which were characterized by the traceable development of fracture and joint fissure on the karst platform.
(3) Neotectonics was the internal driving force in the forming of platform-canyon karst landform
The Himalayan neotectonic movement starting from the Tertiary period made the crust in the region uplift and caused such effects as gradually lowered base level of erosion, intensified hydrodynamism, denudation, erosion and corrosion. Consequently, the flowing water cut off the weak fissure zones between high-angle joints, fissures and fractures, forming the unique landform consisting of deep-incised canyons, cliffs and karst walls.
(4) Warm and humid climatic conditions are the external driving force in the forming of platform-canyon karst landform
The geopark has a subtropical monsoon climate, with an annual mean temperature at 15.8 -19.5℃ and annual mean precipitation of 1600 - 1800mm. The abundant precipitation provides adequate surface and underground runoff while higher temperature helps the interaction between water and rocks, accelerating the underground corrosion and surface erosion in the karst region. In addition, warm and humid climatic conditions are favorable for flourishing vegetation and the concentration of corrosive CO2 contained in the water is up to 6.6 - 9.9 mg/L, having strong corrosion .
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