云南石林洞穴发育特征

THE CHARACTERISTICS OF CAVE DEVELOPMENT IN SHILIN

石林位于滇东喀斯特高原南部,喀斯特极其发育,以发育了典型的石林地形而闻名遐迩,倍受国内外喀斯特学者的关注。洞穴是本区广泛发育分布的一种喀斯特地下形态,类型多样。依据它们的剖面形态、成因和所处的地貌部位差异,将其划分为罅状洞穴、水平洞穴和倾斜洞穴三个类型。洞穴在发育分布上受到区域碳酸盐岩地层分布的控制,表现出洞穴分布的相对集中性、洞穴发育对地层的选择性和洞穴发育的成层性等特征。洞穴发育规模绝大多数为中小型洞穴;洞穴多为现代地下洞河,埋藏浅且多天窗,并且洞穴的发育延伸方向明显受裂隙构造的控制。通过对石林地区喀斯特洞穴发育条件、洞穴发育类型、分布特征和洞穴发育的古地理环境特征分析,论述了石林地区洞穴的发育特征。

Shilin County, which got her name after Shilin karst formed, is 86 km south of Kunming, the capital city of Yunnan Province. The karst area covers 900 km2. Among them 350 km2 are Shilin karst landscapes, which has been set as statelevel natural protected area. Cave is one of the most developed karst features, too. From 1995 to 2000, around 70 caves were explored. Based on their section shapes, location and hydrogeological settings differences, they could be classified into three types of caves. The first type is fracturelike cave, formed by the enlargement by water along fractures. There are innumerable such type of caves developed in Shilin landform areas. Such type of caves is small, 0.5～2 m wide and 20～40 m deep. Strictly, the cave was the outcome of Shilin evolution. The second type of cave is horizontal caves, which mainly developed in the Fengcong shallow depression landscape areas, right outside of Shilin landscapes. Those caves are very complicated, in view of their shapes or genesis. The third type is slope caves, and they mainly distribute at Fengcongdepression karst areas or hillsides of lower mountains, where ground water table is around 100～150 m deep. The cave is commonly connected with vertical shafts or collapse dolines as entrance. The fast flows play a great role in the formation of such type of cave. Generally, the cave development in Shilin County enjoys the following characteristics: (1) The cave development mainly concentrates in three elevation zones. (2) The development of cave is strongly controlled by the lithology of carbonate rocks. Most caves developed in Permian and Carboniferous carbonate strata areas. (3) Small and medium scales caves dominate absolutely. (4) Most caves have active water flow and are at the near water table stage. As the ceiling rock of caves is very thin, karstwindows are well developed. Most caves are water caves, which are normally shallow buried and (5) the orientation of cave passage obviously controlled by structure fissures and there is a great difference between caves of the east and west part of the region. In west, the orientations of caves are dominant by SN or near SN direction. But in east the WE or near WE orientations are predominant. The three water tracing tests in Tianshengguan area, the northeast part of Shilin have revealed the complicacy of underground cave system of this region: the Northsouth and Westeast underground water systems coexist. In lowwater period, the Westeast conduitfissure system works very well, but during high water level, some water drains in NS direction. Obviously the caves show different stages of paragenesis. Caves suffered the alternation of several periods of deposition and periods of fast water flows and flood water.