Evidence for the transition to an oxygen-rich atmosphere in the Rooiberg Group, South Africa — A note

The Rooiberg (Felsite) Group is a rare example of a conformable succession that apparently spans the period of evolution of an oxygen-rich atmosphere. This conclusion is reached indirectly from a review of the Proterozoic stratigraphy of South Africa, and directly from a consideration of the Rooiberg itself. The atmospheric transition coincides with the stratigraphic interval between the dark silicic lavas and associated grey volcaniclastics of the Damwal Formation, and the overlying red rhyodacites and intercalated red-bed sedimentary rocks of the Selonsrivier Formation. Radiometric age measurements indicate that this transition occurred after 2224 ± 21 Ma but before 2090 ± 40 Ma.