Dating calcite methods

Bones and teeth, however, are primary archaeological materials and are common to many archaeological sites. Bones bearing cut marks from stone tools are a clear proxy for human occupation of a site, and in the study of human evolution, hominid remains provide the primary archive material. Hence, many attempts have been made to directly date bones and teeth using the U-series method. Unlike calcite, however, bones and teeth are open systems. Living bone, for example, contains a few parts per billion (ppb) of Uranium, but archaeological bone may contain 1-100 parts per million (ppm) of Uranium, taken up from the burial environment. Implicit in the calculation of a date from °Th/U or Pa/ U is a model for this Uranium uptake, and the reliability of a U-series date is dependent on the validity of this uptake model. 

The technological advance that moved speleothem studies into a prominent place in the study of paleoclimates was the development of reliable and accurate methods for assigning absolute dates to individual calcite layers (Thompson et al., 1975). Such methods as U/Th dating and dating are now well established. A brief review is given here only because all of the other speleothem data depend on these techniques to establish time scales. 

Brook et al. (1990) found pollen grains incorporated in the pore spaces within the speleothem fabric. Since the age of the encapsulating calcite could be determined by U/Th methods, the age of the pollen could also be determined far beyond the usual limitation of carbon-14 dating. From pollen speciation in speleothems. Brook et al. concluded that the Chihuahuan Desert of southwestern United States and the Kalahari Desert of northwestern Botswana were wetter during northern hemisphere glacial and interstadial times. In contrast, wetter conditions in the Somali-Chalbi Desert corresponded with interglacials and to a lesser extent with interstadials. 

Ford, D. C., Thompson, P. L., and Schwarcz, H. P., 1972, Dating cave calcite by the uranium disequilibrium method some preliminary results from Crowsnest Pass, Alberta, International Geography 1972—La Geographie Internationale, Technical Program Abstracts - International Geographical Congress 22 21. 

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