The Precambrian Evolution of the South American Cratonic Margin South of the Amazon River

Abstract

The continued progress in geologic mapping in South America of large areas previously poorly known, the compilation of regional charts, and the growing number of radiometric age determinations has made it possible to outline the major structures of the Precambrian, and to begin to explain the geologic history of the cratonic areas. This can be done with greater confidence for the upper Precambrian, here considered as being the time interval between 1800 and 570 m. y.* Older events can only be clearly recognized in small areas, as, for example, in the northern part of the Guyana shield.