AGE OF CAVES

   The ages of individual caves may vary enormously. In most regions the youngest cave passages have reached their present dimensions during the last 10,000 years, or since the last Pleistocene glacial retreat. In higher latitudes most caves can be related to erosion during the later Pleistocene climatic variations of the last million years, and older caves have largely been removed by continuing surface lowering. In tropical regions less interrupted erosion conditions have encouraged survival of older caves; the Mulu caves of Sarawak include large passages at least two million years old. Relict caves hundreds of millions of years old may survive in some buried limestones, but are commonly filled with younger sediments (see neptunian deposits), minerals or, very rarely, igneous rocks. These fill materials may themselves be dateable, either on the basis of contained fossil material (including pollen), by comparison with similar rock types that occur at the surface or by isotopic age determination methods identical to those applied to suitable surface rock materials. See also dating of cave sediments [9].