Calibration of radiocarbon dates for the late pleistocene using U/Th dates on stalagmites

Twenty paired ¹⁴C and U/Th dates covering most of the past 50,000 yr have been obtained on a stalagmite from the Cango Caves in South Africa as well as some additional age-pairs on two stalagmites from Tasmania that partially fill a gap between 7 ka and 17 ka ago. After allowance is made for the initial apparent ¹⁴C ages, the age-pairs between 7 ka and 20 ka show satisfactory agreement with the coral data of Bard et al. (1990, 1993). The results for the Cango stalagmite between 25 ka and 50 ka show the ¹⁴C dates to be substantially younger than the U/Th dates except at 49 ka and 29 ka, where near correspondence occurs. The discrepancies may be explained by variations in ¹⁴C production caused by changes in the magnetic dipole field of the Earth. A tentative calibration curve for this period is offered.