Age determination of travertine from archaeologic sites

Where travertine has formed by slow passage of calcite saturated water on to archaeological sites, the deposits of cultural materials may be enclosed within material which is datable by a number of isotopic methods. Th-230/U-234 dating is generally applicable for travertines which are not contaminated by detritus, not too porous or permeable, and containing more than 0.1 ppm of uranium. Travertines containing 1 ppm U or more can be also dated by Pa-231/Th-230 methods. The presence of detritus may result in contamination of the sample by varying amounts of U and Th ; the latter can be recongnized by the presence of Th-232 in alpha spectra and various procedures for adjusting data to correct for Th-contamination are presented. Dates for sites ranging in age from 10.000 to greater than 350.000 yerars have been obtained for sites in Europe, Asia and North America. The use of U-234/U-238 ratio measurements, independent of knowledge of initial ratios, may now also be possible for samples of sufficiently high U content ; the ana- lysus depends on the recognition that "hot" atoms of U-234 are more readily leachable than atoms deposited at the time of formation of the sample. Leaching of the sample allows discrimination between these populations. Coupling of U-series dating with either thermoluminescence or electron spin resonance dating may extend the range of applicability.