以云南石林喀斯特洼地灰岩水平凹槽为模拟对象,用氧化钙粉柱(CaO)和岩盐柱(NaCl为主)进行水平凹槽发育实验。实验结果表明,在流动湖水、水渠、静水湖泊和湿地中形成了半环形颈状水平凹槽、环形颈状水平凹槽、倾斜凹槽、双层水平凹槽,湖岸高坡土层中不发育凹槽。岩盐柱溶蚀水平凹槽深度发育速度(1.2~4.56 cm/h)大于钙粉柱水平溶蚀凹槽发育速度(0.000 4~ 0.008 9 cm/h)。相同成分岩石的水平凹槽发育速度在流水和静水中的差值为3?22倍,水中发育速度是土层中的2倍。石林地区喀斯特洼地石灰岩凹槽类型多样。实验和调查结果对比,发现能指示湖泊湿地水位变动凹槽类型主要有半环形颈状水平凹槽、环形颈状水平凹槽、环形半曲面凹槽,分别对应湖泊岸坡、湖泊、湿地中心。实测水平凹槽平均深度63.9533.40 cm。用碳酸盐岩综合侵蚀率(化学溶蚀率的1.5倍,135 mm ? ka~(-1))与气岩界面溶蚀率(5.2 mm ? ka~(-1))的差值(129.8 mm ? ka ~(-1))为水平溶蚀凹槽发育速率,算得到石林喀斯特洼地石灰岩水平凹槽持续发育时间为4.922.573 ka。据此推断,约5 000年前,石林喀斯特洼地石灰岩底部开始发育水平凹槽,湖泊湿地密度16 % (0.15 km~2 / km~2),属高原喀斯特湖泊湿地区,现今湖泊湿地密度不到0.5 %。这有可能表明研究区从5 000年前的湿润降雨丰沛期转向了现代干湿季气候与人类强烈活动干扰,湖泊湿地面积发生深刻变化。
英文摘要:
This study simulates the corrosive effects of water on the development of horizontal karst grooves with analogous cases to the karst depressions in Yunnan Shilin area, China,by using testing pillars made of calcium oxide powder(CaO) and halite (NaCl),respectively. Experimental results show that semi-circular bottleneck-shaped horizontal grooves, annular bottleneck horizontal grooves, inclined grooves,and dual-layered horizontal grooves formed,respectively,under the environments of moving water of lake,canal,stagnant water lake and karst wetland. No grooves developed in the soil layer along the lakeshore high concave slopes. Moreover,the growth rate of horizontal solution grooves in halite pillar (i. e. 1.2?4.56 cm/h) was much higher than that of calcium powder one (as 0.0004?0.0089 cm/h). Meanwhile,in the pillars of same materials,the solution groove growth rate in flowing water was 3?22 times as much as that in stagnant water; and the rate in water was two times as much as that in soil with normal moisture content. There are diverse types and extremely large quantity of solution grooves developed in the karst depressions and karst lakes 8&- wetlands in the Shilin area. Among them,the horizontal grooves, with the shapes of semi-circular bottleneck, annular bottleneck and annular half curved face,respectively reflect the fluctuated water environments as lakeshore and central areas of lake wetland,where the measured average depth of the solution grooves is 63.9533.40 cm with significant differences with sites and altitudes. The average corrosive rate of solution grooves can usually be presented by the difference value of the integrated corrosive rate of carbonate rocks (i. e.,135 mm ? ka~(-1),or 1.5 times of the chemical dissolution rate of the carbonate rocks) and the air-rock interface's corrosive rate (i. e. 5.2 mm ? ka~(-1)). from which the growth time length of the horizontal groove can be sorted out. As a result, the mean growth time length of the limestone horizontal grooves in the Shilin karst depression area is about 4.922.573 ka. Accordingly, it can be speculated that the horizontal grooves were initially produced around five thousand years ago at the rock bottom in the karst depressions; at that beginning stage, the areal density of the karst lakes wetlands was 16% in this area which belonged to karst lake/wetland plateau landform with a year-round humid and high rainfall climate. However, at present, the density has been reduced to only 0.5% due to the dramatic change in the areal size of lakes & wetlands, which also implies the heavy impact of climate change and intensive human activities on the karst environment.