Karst environments preserve some of the best archives of past climate, vegetation, hydrology, human impact, landscape evolution, volcanism and tectonic evolution. Much research has been carried out since the works of Ford and Williams (1989) on karst geomorphology and hydrology, as well as dating of karst deposits. Since the last decade of the 20th century, research has focused on the extraction and interpretation of climate and environmental proxy data from karst archives, in particular from stalagmites. The nature of the karst environment, and karst processes provide all the ingredients necessary for the capture and preservation of environmental signals (Fairchild et al., 2007). The aim of this chapter is to illustrate the link between surface and subsurface karst processes which result in the formation of unique archives that record a variety of physical and chemical proxy data that allow the reconstruction of past climate and environmental changes, including variability in the carbon cycle. Karst environments are regions where sparingly soluble rocks outcrop and efficient acid hydrolysis creates spectacular dissolution landforms. The release of CO₂ from karst waters to the atmosphere causes precipitation of calcium-carbonate deposits, which, in caves, are collectively known as speleothems. Karst carbonate deposits capture climate and environmental signals in their macro- and micro-morphological characteristics, their mineral composition, and their chemical properties. They can be precisely dated with radiometric techniques and, thus, constitute an archive of climate change for millions of years. Karst carbonate formation is a product of both inorganic and organic processes. The influence of bacteria appears to be particularly important in the formation of calcareous tufa, deposits which commonly dam flowing water at both surface and subsurface. Bacteria also play a role in favouring the growth of mineral fibres in cave moonmilk, a plastic and powdery deposit consisting mostly of water and calcite. The most typical products of deposition in the subsurface karst environment are speleothems consisting of a rigid and relatively fragile arrangement in successive layers of calcium-carbonate crystals, which are here referred to as sparitic speleothems. Stalagmites, stalactites and flowstones mostly consist of calcite, and less commonly of aragonite or other minerals, which reflect events that occurred at the surface in their fabrics, trace-element composition, stable-isotope ratio and organic chemistry. The focus of this chapter is on issues related to the formation of karst deposits and their significance as palaeoclimate archives.
Carbonates in Continental Settings: Facies, Environments, and Processes p. 269-318