REFLECTIONS ON THE 230 Th/U DATING OF DIRTY MATERIAL

Abstract

High correlation coefficients between the activity ratios of the uranium and tho- rium isotopes common for the Nisochroni approach of 230 Th/U dating of dirty material mask the requirement to check for closed-system conditions of uranium in addition to the detrital correction of 230 Th/U ages. The difficulty to calculate standard deviations of 230 Th/U dates derived by the Nisochroni approach complicates the problem. The methodical reasons are discussed. Closed-system conditions are checked by the 234 U/ 238 U n 230 Th/ 238 U AR plot which can also be used to carry out least-squares fitted detrital correction of 230 Th/U ages of dirty material.