地质与地貌条件对岩溶系统的控制与指示

Geological and geomorphologic settings acting as the controlling factors and indicators for karst systems

岩溶系统的发育与分布在很大程度受地层、构造、地形和地貌条件等因素的综合控制与影响,地层因素包括可溶岩的矿物组分、结构及其与其他岩性地层的组合关系,矿物组分和结构决定了岩石的可溶性、孔隙度和渗透率,并影响岩溶发育的进程;根据岩性组合特征,可将同一地层划分,或将不同地层合并为含水层、隔水层或弱透水层。构造因素包括褶皱、断裂和裂隙,褶皱和断裂控制了岩溶水流系统的内部结构和边界特征,而层面、节理和小型裂隙组成的三维裂隙网络是岩溶水流入渗的优先通道,也是岩溶发育的先导。尽管大型岩溶地下河系统的发育与分布与地形无关,但地形控制了区域水文基准面,进而控制了岩溶发育的深度以及地下水的排泄模式,而且根据地形调查可确定外源水的边界范围。岩溶地貌和岩溶形态发育既是地质条件的集中反映,同时又可为地下岩溶空间发育和岩溶水流分布提供指示,但有些岩溶地貌和形态是古岩溶作用的产物,与现代岩溶水文系统并不发生直接联系,因此,岩溶地质调查还应综合分析区域地质和地貌演化史。

Geological and geomorphologieal settings are indispensable for the karst system development. The bulk mineralogical compositions and internal structures of soluble rocks control the chemical solubility, primary porosity and permeability. Based on the associations of the soluble rocks with other insoluble ones, lithostratigraphy can be transformed to hydrostratigraphy： aquifer, aquiclude or aquitard. Tectonic factors, such as folds, faults and fractures, control the internal structures and boundaries of a karst system. Water movement in hard rock aquifers mainly occurs in a network of fractures and bedding planes, which constitute zones of preferential infiltration and pioneers for karstification. Although subterranean rivers are largely independent of topography, the topography is of great importance, as it defines the hydrologic base level and thus guides the regional orientation of the drainage pattern. The catchments of sinking streams originating on non - karst formations can also be delineated on the basis of topography. Karst landforms not only be restricted by geological settings, but provide indications on the karst development and hydraulic properties of the aquifer. Karstification evolves over time, and the climatic and topographic conditions also change over time, which may result in changes in the base level and flow directions. The present underground drainage pattern of a karst system can often only be understood by considering its landscape history.