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A glaciacao jequitai : um guia estratigrafico para o pre - cambriano superior no brasil

1981; Sociedade Brasileira de Geologia; Volume: 11; Issue: 1 Linguagem: Inglês

10.5327/rbg.v11i1.205

2317-4889

J.G.P Couto, L Bez,

Paleontology and Stratigraphy of Fossils

Based on recent radiometric ages determined for the so called and on litogical and stratigraphic descriptions of glaciogenic rocks a new stratigraphic division is suggested for the Upper Precambrian in Brazil. A restrition to the Bambui Group is proposed taking its base as defined by the Paraopeba Formation (Carrancas Member included) made up of carbonated (primarily limestones and subordinate dolomites) and pelitic rocks. The rock sequence, composed primarily of dolomites, that crops in the Vazante/Paracatu region is dropped from the base of the Bambui Group. With this statement becomes clear that the several interpretations correlating the Bambui and Macaubas Groups have to be revised. The correlation of the stromatolites, described by School (1976) in Couto Magalhaes and located below the glaciogenic rocks with the stromatolites that crop in the Vazante/Paracatu region, is possible taking into account as belonging to a same unit and deposited before the Bambui Group. It is easy now to understand that between this unit, located below the tillites, and the Bambui Group, both deposited in warm climate, as showed by the stromatolites, one or more glaciations occurred. The age of this glacial event is comprised by the time interval of 640 m.y, (age of Bambui Group base above the tillites in Jequitai region) and 950-1,350 m.y (age of the stromatolites below the tillites in Couto Magalbaes region). The name Jequitai Glaciation is suggested for this event. As a consequence of the data presented a new approach for mineral exploration in the Upper Precambrian rocks in Brazil has to be worked out.