第三系红层下石林的岩溶动力学特征

KARST DYNAMICS FEATURES OF STONE FOREST UNDER THE TERTIARY RED CLASTIC ROCKS

区域地球化学表明 ,第三系泉水及直接被第三系覆盖的灰岩泉水的SIC在雨季小于 0 ,在旱季大于 0。在祭白龙洞 ,地表被第三系覆盖洞段滴水的暂时硬度比地表无此覆盖层的滴水小 1 .6～ 3mmol/L ,pH值也较低。第三系盖层中空气CO2 浓度为 1 0 0 0 0～ 1 4 0 0 0mg/m3,随深度下降。第三系的裂隙最大渗透张量为 0 .0 2～ 0 .0 5m/d,高于石灰岩。野外溶蚀试验结果 ,第三系盖层中石灰岩的溶蚀速率为 1 .5mg/ 1 0 0d,且垂直溶蚀速率与水平溶蚀速率相当。上述特征表明 ,较高的裂隙渗透张量及随裂隙下渗的富侵蚀性的水是石芽、石林发育的两个重要因素。

Stone Forest in the Shilin Scenic Area, Shilin Yi Nationality Autonomous County, Yunnan Province is one of the famous sword-like pinnacle karst features in the world and it is developed in the limestone, dolomitic limestone and dolostone of the Qixia and Maokou formations of the Upper Permian, which were directly covered by the Tertiary red clastic rocks. So, limestone, dolostone and the Tertiary as one of the insoluble covers (the other, basalt) constitute a special karst dynamics system different from the naked karst dynamics system. What is this particular karst dynamics system characterized by? Regional hydrogeochemistry showed the SIC (saturation index of calcite) of spring water from the Tertiary and limestone directly covered by the Tertiary was smaller than zero in rainy season and larger than zero in dry season. In Cave Jibailong, the temporal hardness of cave drop water from the section covered by the Tertiary on the surface was 1.6-3 mmol/L less than that without the Tertiary covers on the surface. The pH was lower, too. CO2 in the Tertiary cover air continuously declines with depth. Maximum fracture permeability tensors of the Tertiary are 0.02-0.05 m/d, larger than those of limestone favorable for the downward percolation of erosive water. The solution test in the field showed solution rate of limestone of the Tertiary was 15.2mg/100d, higher vertically than horizontally. These features suggest that higher fracture permeability and aggressive allogenic water percolating down the fissures are two important factors for the development of stone forests. This is why well-developed stone forests often appear together with a small area of Tertiary red clastic rocks.