John C. Vogel

Calibration of Radiocarbon Dates for the Late Pleistocene using U/Th Dates on Stalagmites

Twenty paired 14C 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 7ka 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.

Suitability of Ostrich Eggshell for radiocarbon dating

Ostrich eggshell from archaeological sites remains largely free of more recent carbon contamination and as such is suitable material for radiocarbon dating. The carbonate fraction of the shell does, however, display an initial deficit in 14C, which causes the ages to appear 180 ± 120 yr too old.