Constraining the age of the Iporanga Formation with SHRIMP U-Pb zircon: implications for possible Ediacaran glaciation in the Ribeira Belt, SE Brazil - Campanha, Ginaldo Ademar da Cruz; Basei, Miguel Angelo Stipp; Tassinari, Colombo Celso Gaeta; Nutman, Allen; Faleiros, Frederico Meira (Gondwana research, 2008)