侵蚀型天坑演化研究

Evolutional process of erosional tiankengs

中国天坑研究学者通过系统调查,确立“tiankeng”作为标准地貌术语,并规范其形态特征,提出塌陷型天坑和侵蚀型天坑两种成因类型。文章以重庆武隆箐口天坑、陕西汉中伯牛天坑、马达加斯加安卡拉那高原的曼格里(Mangily)天坑、巴布亚新几内亚穆勒高原的阿底(Atea)天坑为研究对象,通过对比分析4个天坑(群)发育的地层结构、地貌演化和水文地质特征等,论述侵蚀型天坑系统演化的共性特征,即三元或二元地层结构、深厚包气带和巨大地势差异、覆盖型岩溶分布、覆盖层对雨水的汇聚或夹层对地下水的汇聚等。基于侵蚀型天坑的成因条件,认为其发育阶段可分为:落水洞-竖井(地下河)阶段、侵蚀-竖井状大厅阶段、崩塌-天坑形成阶段和天坑退化阶段,并对侵蚀型天坑演化机理提出新的认识。

In this paper,the common features of the erosional tiankeng are discussed by comparing the stratigraph⁃ic structure,geomorphic evolution and hydrogeological characteristics of four tiankengs in the world,i.e.,Qingk⁃ou Tiankeng in Wulong karst of Chongqing and Boniu Tiankeng in Xiaonanhai Plateau of Hanzhong,China,Mangily Tiankeng in Ankarana Plateau,Madagascar,and Atea Tiankeng in Muller Plateau,Papua New Guinea.The current study indicates that the erosional tiankeng is commonly characterized by ternary(sandwich)or binary stratigraphic structure,covered-karst distribution,deep vadose zone and great topographic differences,as well as catchment of rainwater by the overlying layer.Based on these genesis conditions,when the surface water converg⁃es and flows into the soluble rock aquifer to form underground karst cave,its evolutionary stages can be divided in⁃to(1)sinkhole-shaft(underground river)stage,(2)erosion-shaft-chamber stage,(3)collapse-forming tiankeng stage,and(4)tiankeng degradation stage.The genesis analysis of erosional tiankeng provides a new in⁃sight into its evolutionary mechanism.