Arid Zone Palaeoenvironmental Records from Cave Speleothems

Solution caves and speleothems are common in many of the world’s arid areas. Speleothems can be accurately dated to at least 500 k yrs B.P. and can provide a wealth of palaeoenvironmental data. In areas almost too dry for speleothem growth today, the frequency of ages for relict formations provides evidence of past periods of increased moisture. Speleothems now under water because of a rise in the groundwater level, provide information on past drier periods of climate when water levels were much lower than they are today. Speleothems may contain pollen and other plant microfossils even when the clastic cave sediments and sediments outside the cave do not. In deserts, where pollen grains are rarely preserved in the highly oxidizing environment, cave speleothems are potentially a major source of palaeovegetation data. Many arid-land caves have poorly ventilated passages with close to 100% humidity. These passages may contain stalagmites laid down in isotopic equilibrium with the precipitating waters. The oxygen, carbon and hydrogen isotope characteristics of these formations can provide relative or absolute palaeotemperature data, information about the air masses that brought rainfall to the cave in the past, and information on the relative importance of C 3 and C 4 plants in the vegetation cover above the cave over time. Finally, it is now clear that caves in semi-arid areas may contain stalagmites with annually deposited layers, the thickness of which may be a proxy of annual precipitation. Such deposits may eventually provide high-resolution precipitation records that can be used to predict climate into the 21st century.