Earth

Chemical deposits

All caves are filled with more or less large amounts of chemical deposits,   minerals and physical deposits, sediments of various types  which are mostly transported by water into caves. These, as a whole, are known as speleothemes, and are a very precious database regarding the geological, environmental and especially climatic evolution of the past.
Chemical sediments form when water saturated with calcium carbonate is subjected to variations in temperature or CO₂ content, or gets concentrated due to evaporation, thus becoming oversaturated. Therefore excess carbonate deposits in the form of concretions, known as speleothemes, which can have various shapes and morphology depending on where they form, the way the minerals precipitate, etc. Most speleothemes are made of calcite, which is surely the most widespread cave-mineral. Almost all speleothemes form in a sub-aerial environment. However, in particular conditions, in small closed basins with over-saturated water, even underwater speleothemes can form. Most speleothemes that can be observed in flooded caves formed in the sub-aerial zone, and were subsequently brought to the phreatic zone thanks to a flooding of the conduits with fresh or salt water, or as a consequence of a subsequent rise in the base-level.
Speleothemes form more rapidly and more abundantly in warm climates. Growth generally takes place in concentric bands, and their chemical composition (particularly with regard to the oxygen isotopes) is controlled by that of both water and atmosphere in which they formed. Therefore they provide  important data regarding the climate of the past.