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1. Bolsista do CNPQ Brazil-Programa de Pós-Graduacāo em Geociencias, Institute de Geociencias, UFRGS, Agronomia, Caixa Postal 15001, CEP 91501-970, Porto Alegre, RS, Brazil; 2. Johann Wolfang Goethe University, Institute of Geology and Palaentology, Frankfurt/Main, D-60054 Germany; 3. Institute of geology, University of Tuebingen, Tuebingen, D-72076 Germany |