Karst

Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves.[1][2] It has also been documented for more weathering-resistant rocks, such as quartzite, given the right conditions.[3] Subterranean drainage may limit surface water, with few to no rivers or lakes. However, in regions where the dissolved bedrock is covered (perhaps by debris) or confined by one or more superimposed non-soluble rock strata, distinctive karst features may occur only at subsurface levels and can be totally missing above ground.[4]

Škocjan Caves, Slovenia
Global distribution of major outcrops of carbonate rocks (mainly limestone, except evaporites)
The Puerto Princesa Underground River, Philippines

The study of paleokarst (buried karst in the stratigraphic column) is important in petroleum geology because as much as 50% of the world's hydrocarbon reserves are hosted in carbonate rock, and much of this is found in porous karst systems.[5]