1. Department of Earth and Planetary Sciences, University of California, Davis, California 95616, USA
2. Berkeley Geochronology Center, Berkeley, California 94709, USA
3. Department of Geosciences, University of Wisconsin, Milwaukee, Wisconsin 53211, USA
4. Departamento de Geologia, Universidade Federal do Paraná, Curitiba, PR, 80060-000, Brazil
5. Departamento de Paleontologia e Estratigrafia, Universidade Federal Rio Grande do Sul, Porto Alegre, RS, 90040-060, Brazil