The Study On The Features, Development And Evolution Of Karst Morphology In Lower Reaches Of Wujian

There are large,widely distributed karst areas and variety of karst landforms.in China. the area of carbonate rocks (including buried below non-soluble rock), is 3.46 x 106km2, about 1/3 of land area of China. and there are variety of types karst, generally speaking, these types can be divided into four types:subtropical karst of South China, arid and semiarid karst of North China and temperate semihumid karst of northeast China Alpine karst on Qinghai-Tibet Plateau.There is international significance on the work of Karst landform in China. Compared with the Karst areas elsewhere in the world, the Karst forms of China is more colorful, distinctive. because the development of karst landforms in China has mre unique advantages.that is to say:the backgrounds for the development of karst in mainland China are characterized by:i,hard,compact carbonate rocks ii,strong Cenozoic uplift; iii,heat-moisture matching monsoon climate;iv, without scouring actions of continental ice sheet of the Last Glaciation. All these backgrounds make the karst forms of China have preserved before Traissic; and have a long, continuous history of karst development.The subtropical karst of South China has been known as the continental tropical-subtropical karst "museums and textbooks, so it is important in the work on the karst geomorphology of China. In July 2007, the south China Karst had been officially recorded in UNESCO's "World Natural Heritage List " by UNESCO, and the karst valley of lower reaches of Wujiang had also been recorded in this list as the representative of the subtropical karst valley.The study of development and evolution of karst landform of the of lower reaches of Wujiang is very important that we how know karst features of subtropical gorge regions is developed and evolved。but now the study is still very weak.The study method of Karst feature complex is be applied in the Karst morphology study of the of lower reaches of Wujiang, and this method can avoid the confusion that the same form of different innate character brought about in the Karst morphology study. In order to explore the evolution process of this area, the characteristic of Karst feature complex typical locations of the steeped landforms will be studied and will be combined to the development stage of karst landforms.The key research of the evolution of karst landforms is to study the characteristic of depositional forms. The combining analysis of the dissolutional and depositional forms, we can know karst landforms evolution process of this area through the study of the characteristic of depositional forms of typical place.On the study of the controlling factor of the development of karst landform, this study apply Karst Dynamics system(KDS) to explore causes of karst landforms evolution.these causes can link with interaction of lithosphere, hydrosphere, biosphere and atmosphere, so the development and evolution of karst forms can be controled by internal and external forces.Conclusions as the following are drawn:(1)There is a large scale of karsts geomorphology and possesses a unique subtropical mid-mountain karst gorge characteristic,enriched abundant surface karst represented by cone fengcong-depression, giant doline, gorge, natural bridge, and underground karst represented by giant caves and secondary speleothems. It perfectly display typical multitype and multilevel karst features of subtropical deep incising gorge regions.(2)The Karst feature complexs on the different topographic surface are products of different developmental stages of karst landform. Exi Phase (Higher Plateau Phase) in the three gorges areas. kept in the watershed regions of 1700m to 2000m above sea level, At present the Karst feature complexs of earth surface of this phase are represented by combination low peaks, Karst platform with large polygons and Shallow dish depressions.The feature of the peaks is rounded and the distancing between two peaks is high,about 500m;there are little caves, who are small; there developed red clay on karst platform. all these reflects a elderly period of karsts development period. and formed e from the Paleogene to the early stage of neogene, The lower planation surface of 1200～1500m above sea level, the feature of earth surface of this phase is tall peaks and large depressions, the height between peak and the table is 25～35m or so, and distancing become smaller and is 300-400m. there developed karst caves and abundan secondary deposits. are be found in it. Its surface deposits is red soil, in some places,weathering crust of iron was found;this reflects a maturity period of karsts development period. The erosion surface of 500-800m above sea level, the marked feature is Peaks-trough valley, valley; the height between peak and depression is 25～35m or so, and distancing become smallest and is only 250m. the peak,s bases are closely linked, the features of peakis not the typical, the top is fat and Preserve the original characteristics of geomorphic surface; Its surface deposits is yellow soil. All this reflects young period karsts development period.(3)All the karst features of lower reaches of Wujiang, are the reflection of its special lithological, Stratigraphical, tectonical, topographical, hydrodynamic conditions,climatic background, neotectonics movement,as well as long term karstification. the dominant factors of development of karst landforms are neotectonics movement. hydrodynamic conditions and climatic background.To study on karstification intensity and its variation under different geological settings, we come to conclusion:under previous climatic conditions, the karstification intensity on Exi earth surface is weaker than Pengdi's, this indicate the Karst feature complexs of Exi have developed very long time and its form can be attribute to the latest period Tertiary dry Climatic conditions; the karst features of Pengdi's surface is younger than Exi's and Shanyuan's, may be develop short time.Under the influence of neotectonics movement, the features of the study area manifest Multiple generations and karst gorges and planation surfaces appear alternately; at the same time, the planation surfaces are to be transformed different intensity by the later tectonic movement and its features on the different setting appear characteristic. In the dividing ridge far away from modern water-draining ground, grounding integration is still favorable because the geomorphology is not largely affected under the periodically--enlivened, and the karsts geomorphology here mainly represents cone fengcong-depression. However, most region, which is affected by the periodically—enlivened, that Higher Plateau Phase and Hilly Plateau Phase were uplifted to different altitude, so river drainage systems began to cut down on the hilly plateau phase earth surface to form gorges with steep banks and releases a scenery of core-shaped karst topography and reflects a youth period of karsts development period. Some places, but in minority, are still in the middle period. Therefore, The variety of distribution and combination karst geomorphic features can reflect the evolution history of karstification processes.(4) It involved three evolved stages of Exi stage, Shanyuan stage, Pengdi stage and Gorge stage to form the geomorphic framework including karst leveling plane and dissected gorges in the lower reaches of Wujiang,We have a more clear understanding the features, development and evolution process of of subtropical karst gorges because of the study on karst gorge in the lower reaches of Wujiang, so, this study sheds light on the formation and evolution of the Yangtze River Three Gorges. Meantime, the karst landform, s evolution of the lower reaches of Wujiang is affected by neotectonic movement and hydrodynamic conditions, this make erosion and corrosion to Superimpose, and to make the development intensity increases, all this can form beautiful Wujiang river gorge, but to make the ecological environment become more fragile, this bring up to some disasters such as flood and drought, soil erosion, desertification, land subsidence and so on. We also note that there are the role of different karstication intensity and role in different settings,and this imply us that we must know the karst landform different features of the different surfaces and karst geoge in land use, water resources development,and environmental protection.