关键词: 喀斯特;形态结构;洞穴成因

Abstract: The Shiliping area where Panxian Dadong cave site is located a t is situated in south- eastern Panxian County of Guizhou Province. This area is o n the dividing crest between the Wuduhe Riv er of the Beipanjiang drainage and the Mabiehe River of the Nanpanjiang drainage. The karst landscapes, in terms of morphometry , belong to the humid tropical karst. They are characterised by a combination of clustered cones and depressions, valley s and poljes, a typical karst of peak-cluster depression in China. The cones are found to be almost constant in slope angle ( 41°— 44°) and generally symmetrical in plan. The Late Tertiary was a very karstic and caverous period in the carbonate rocks of this area. The later tectonics are significant. With the great uplift of the neotectonics accompanied by the active incision of major rivers, the karstificatio n by erosion and corrosion proceeded vertically rather than horizonally as the surface and g round water in this area try to follow a lowering of the base-level and a thicking of the vadose zone. Under conditions of this increasing available relief and hence potential energy driving groundwater circulation, it is possible for any types of karst landforms at any stag es to evolve toward peak-cluster depression karst in an abnormal sequence and to exist in a steady state of developments. With the intermittent uplift accompanied by the frequent changes of base-level, alternating karstification in both vertical and lateral way s resulted in many times of headwater erosion and subsequent surface-levelled landforms and caves. The effects then spread from the low er reaches of trunk riv er to the upper reaches and from the major g org es to the plateau interfluves. In this uplifted and mountainous area, when the overlying classic rocks were stipped, the major rivers would a t first cut across the limestone surface. Eventually , large faults or fissures will become foci for infiltration of water and a part or all of the stream will disappear underground. This break-up of the fluvial system will be accelerated by the neotectonic uplift, which will low er the water table, empty the caverns and allow more water w ell seep into the rock. The infiltration points then will develop into a series o f do-lines and hence enclosed depressions. As a result, the disappearance of fluvial karst in allogenic area is a major hydrodynamic factor in the formation of peak-cluster depression (valley) . The vertical infiltration and lateral movement of the allogenic water are basically sure of cave formation and passage-leveled features. The alternations o f dry-wet and cool-warm climates in Quaternary may have played a n important part in the relic features o f peak-cluster depressions, valleys, and in the related speleo them types in caves. However, the landscape is still a sort of the tropical karst.

Key words: Karst, Morphometry , Speleogenesis