Abstract: Shuanghe area have a lot of caves, Shuanghe cave system is longest one. Lithological characters, structure and hydrology control the cave development. Among them, gypsum layer that contained in the stratums is a key factor. Formation process of Shuanghe cave system has four phases. Key Words: Shuanghe cave system, formation factor, evolution process
1. Introduction
Guizhou Province is located in the southwest of China. Shuanghe cave system is situated in Suiyang County where is at the north of Guizhou, it is 250 km apart from Guiyang the capital of Guizhou.
Shuanghe area belong to the Yangtze River System, the altitude is between 700 to 1700 m, north is higher than south. Landforms of the area is mainly Fengcong-depression and Fengcong-valley.
This area densely covered by caves. We have found more than 100 entrances, 58 of them have been surveyed, and the total length is more than 100km. The Shuanghe cave system is the longest one in this area.
Shuanghe cave system is a complex cave system what developed in dolomite. It has 23 entrances and consists of many branches and three underground rivers. The general width is 10-20m, general high is around 10m, and the length is 85290m.
2. The Main Formation Factors of Shuanghe Cave System
(1) Lithological Characters
Shuanghe cave system developed in dolomite and dolomitic limestone of Cambrian and Ordovician system. There are gypsum layers in the stratums. Geological map of Shuanghe area
Middle to thick stratums supplies good material elements for developing cave. Gypsum layer is an important factor of cave development. Not only it can be dissolved more easily than carbonate rock, but also it can make rock break while it crystal at the wall and top of caves.
(2) Structure
Shuanghe cave system is located between anticlinal axis and synclinal axis, so stratum dip is gently. There is no big fault in this area, but joint is development.Gently stratum is a good factor for long and huge caves developing. Developed joints benefit to water seep into the ground what developed a lot of branches in Shuanghe cave system. Because there is no big fault, stratum kept integrality, that make the huge cave channel stability.Because Himalayan movement made crust intermittence uprise, it formed several levels in Shuanghe cave system.
(3) Hydrology
Shuanghe cave system is located at the head of Furong River. Underground water flow out to surface as underground rivers. It is a main source of Chiwu River, branch of Furong River.In this area, because stratums contain gypsum layer, water contain SO42- more than general area, that benefit to dissolve dolomite.
Water Chemical in Shuanghe area mg/l K+ Na+ Ca2+ Mg2+ Fe2+,3+ HCO3- SO42- Cl- Shuanghe Water Cave 1.99 0.07 37.95 10.43 0.017 159.44 4.80 3.67 Dayu Spring 2.16 0.07 38.45 12.84 0.022 157.93 15.61 4.08 Yangjiagou Spring 2.24 0.15 37.66 10.31 0.015 150.41 10.09 3.67 Dafeng Cave(drop) 0.87 0.61 53.06 16.65 0.00 207.94 12.3 1.75 Helictite Branch(pool) 5.60 0.89 31.08 11.02 0.00 68.9 65.53 0.88 Gypsum branch(pool) 1.41 0.14 100.38 46.48 0.00 116.36 374.49 0.88
3. Main Evolution Phases of Shuanghe Cave System
Formation of Shuanghe cave system is complex. Through contrast Shuanghe cave system with landforms and analyze the speleothems, Formation process of Shuanghe cave system has four phases.
(1) Paleo-river Phase
This phase is the first phase, only formed some small sinkhole and shift. The landforms phase is Daloushan Phase. Altitude is between 1300 and 1500m.
(2) Shigao Dong Underground River Phase
In this phase, three old underground river systems had formed; they are Shigao Dong Underground River, Mahuang Dong Underground River and Pixiao Dong Underground River. Altitude is between 850 and 1000m.
(3) Shanwang Dong Underground River Phase
Because crust uprise, cave channels of Shigao Dong Underground River Phase became dry caves as lower caves capture. Some new underground river, such as Shanwang Dong Underground River, Lower Shiigao Dong Underground River, Dafeng Dong Underground River and so on, had formed. Altitude is between 800 and 900m.
(4) Shuanghe Suidong Phase
Caves developed to lowest level and connected each other. Shuanghe cave system and today’s underground river system have formed. Altitude is between 700 and 850m.
lipo Publié le : Jeudi 16 mars 2006 @ 15:34:49