岩溶风化壳形成演化及其循环意义

FORMATION AND EVOLUTION OF KARST WEATHERING CRUST ON LIMESTONE AND ITS CYCLIC SIGNIFICANCE

灰岩溶蚀速率快而难溶物含量很低的特点显示岩溶区厚层连续风化壳的形成需要消耗巨厚的碳酸盐岩地层 ,有利于地貌向准平原化方向发展 .由于岩溶作用对地下水动力条件的敏感性 ,在地下水以垂直作用方式为主的地区会出现“土壤丢失”现象 ,导致溶蚀残余物质或地表原有的风化壳转入近地表岩溶裂隙(为石漠化提供了有利条件 ) ,从根本上制约了地表残余物质的长时间积累和连续风化壳的持续发展。所以 ,厚层连续的风化壳只能发育于地下水以水平作用方式为主的水文地质条件下 ,而这种条件从大的时间、空间尺度上只能出现在地貌发育晚期已经接近侵蚀基准的夷平面上 ,因此 ,厚层连续的岩溶风化壳具有明确的旋回意义。

The fact that the dissolution of carbonate is very fast and its residual is very little shows that the formation of a thick weathering crust in karst areas needs to dissolve huge thickness of carbonate rock, and is in favor of peneplanation. In the karst areas where groundwater circulates vertically, a process of 'soil loss' transits residual and/or pristine weathering crust from surface to cracks and cavities in carbonate rocks, consequently it is difficult to accumulate residuals for a longtime on the surface and form a weathering crust. A thick continuous weathering crust in karst areas can be developed under the condition that groundwater circulates horizontally. In a large scale of time and space the mentioned hydrogeological condition exists only on the planation surface near to the base level of erosion in the late stage of a geographical cycle. The continuous thick karst weathering crust is of definite cyclic significance because the sensitivity of karst to groundwater dynamics.