Abstract

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.

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