δ13C and 87Sr/86Sr of phosphorites from the São Francisco Craton, Brazil: phosphogenesis and correlations

Abstract

Phosphate accumulations in the São Francisco Craton are found in both the cratonic non-deformed strata, and in the Brasilia Fold Belt, to the west of the cratonic area. The deposits are stratigraphycally controlled and their formation is probably related to a widespread episode during the terminal Proterozoic Era (Cook and Shergold, 1986). These authors suggested that major phosphogenic event followed a period of glaciation, which “could produce a large volume of cold, nutrient-rich water, resulting in a major expansion of organic productivity in the photic zone following the glacial period”.