Correlation of proterozoic sediments of Western and Central Africa and South America based upon radiochronological and paleontological data

Nearly 70 new Rb-Sr isochron ages and many K-Ar conventional ages have been determined between 1975 and 1980 on Proterozoic sedimentary or metasedimentary sequences in western and Central Africa and South America. Some stratigraphic results have been established: (1) five formations have been dated of the Lower Proterozoic; (2) a long sedimentation gap occurs, mainly in western Africa and in some regions of Central Africa and South America between nearly 1600 and 1100 Ma; (3) the upper Riphean assemblages of stromatolites have been dated and compared to those of the Eurasian craton; (4) two main glacial events have been dated, the first one placed at ca. 950 Ma, the second during the Vendian, at ca. 650-620 Ma; (5) it can be stated that, when applied to Precambrian sequences, all stratigraphic methods must be used together. (Auth.)