Abstract

Criteria concerning sample and analytical data and stratigraphic control have been used in a critical assessment of the suitability, for use in construction of a Phancrozoic time-scale, of radiometric data relevant to the Carboniferous, Permian and Triassic periods. Few of the age determinations available in 1982 satisfy these criteria and many of those used previously as a basis for time-scales for this part of the Phanerozoic are considred unacceptable by present standards. On the basis of this review, ages of 365 ± 5 Ma, 290 ± Ma and 250 © 5 Ma. respectively, are proposed for the beginning of the Carboniferous. Permain and Triassic periods, and 205 © 5 Ma for the end of the Triassic. Radiometric ages are related. where possible, to the principal chronostratigraphic divisions of the rock successions representing those periods.