O GRUPO ARARAS (NEOPROTEROZÓICO) NA PARTE NORTE DA FAIXA PARAGUAI E SUL DO CRATON AMAZÔNICO, BRASIL

Abstract

The Neoproterozoic Araras Group is redescribed and redefined on the basis of facies and stratigraphic data from the northern Paraguay belt and south of the Amazon craton, State of Mato Grosso, Brazil. This predominantly carbonatic unit reaches approximately 600 m thick, overlies glaciogenic diamictites of the Puga Formation and is covered by siliciclastic rocks of the Alto Paraguai Group. The Araras Group succession was divided into four formations: (1) Mirassol d´Oeste, composed of fine-grained dolostone and dolostone with stromatolite; (2) Guia, with fine-grained bituminous limestone, shale and calcareous breccia, locally dolomitized; (3) Serra do Quilombo, consisting of fine-grained dolostone, sandy dolostone and sparry dolomite cemented-breccia and matrix-supported breccia; and (4) Nobres, comprising fine-grained dolostone, dolomitic breccia and conglomerate, sandstone, pelite and layers of secondary chert. The Araras Group was deposited in a platform of deep to moderately deep waters (Mirassol d´Oeste, Guia and Lower Serra do Quilombo formations) and under storm and tidal influences (Upper Serra do Quilombo and Nobres). The Mirassol d´Oeste Formation and the base of Guia Formation, in the southwest of Amazon craton, constitute a Neoproterozoic cap carbonate deposited after the Puga glacial event correlated to the Marinoan episode, within the context of the lowlatitude glaciations according with the snowball Earth hypothesis. The detailed stratigraphic study of Araras Group has established the basis for global correlation of these deposits with other Neoproterozoic post-glacial units around the world.