Direct dating of stromatolitic carbonates from the Schmidtsdrif Formation (Transvaal Dolomite), South Africa, with implications on the age of the Ventersdorp Supergroup

Pb isotopic analyses of stromatolitic limestones from the Schmidtsdrif Formation (Transvaal Dolomite) of South Africa give a late Archean isochron age of 2557 ±49 (2 sigma) Ma. The new date significantly changes the position of the Archean-Proterozoic boundary in the Kaapvaal province and suggests that a possible division of the Transvaal Supergroup is necessary. It also resolves the long-standing controversy about the age of the Ventersdorp Super-group, whose zircon U-Pb date of ca. 2.7 Ga must be more acceptable than the Rb-Sr dates of about 2.3 Ga. Our study provides a new example that demonstrates the great potential of employing the U-Pb systems of carbonate rocks for direct dating of sedimentary sequences.