Chapter 49 The Neoproterozoic Macaúbas Group, Araçuaí orogen, SE Brazil

Abstract

AbstractThe Neoproterozoic Macaúbas Group records accumulation in the precursor basin of the Araçuaí orogen, located on the eastern margin of the São Francisco craton (SE Brazil). The Macaúbas basin evolved from a late Tonian continental rift to a passive margin that lasted at least untilc.660 Ma. It was orogenically inverted during the late Neoproterozoic Brasiliano event. The Macaúbas Group includes the pre-glacial Matão, Duas Barras and Rio Peixe Bravo formations, the glaciogenic Serra do Catuni, Nova Aurora and Lower Chapada Acauã formations, and the post-glacial Upper Chapada Acauã and Ribeirão da Folha formations. In the central sector of the Araçuaí orogen, the oldest glaciogenic unit of the group, the Serra do Catuni Formation, overlies the sandstone-conglomerate package of the Duas Barras Formation. The Serra do Catuni Formation consists of massive diamictite with minor sandstone and rare pelite, deposited mostly in a proximal glaciomarine environment. This unit passes upward and eastward into the Lower Chapada Acauã Formation, a thick succession of stratified diamictite, graded sandstone, pelite, transitional basalt and rare carbonate. This distal glaciomarine unit is covered by the diamictite-free Upper Chapada Acauã Formation, which passes eastward into the Ribeirão da Folha Formation, which includes fine-grained turbidite, pelite and ocean-floor rocks. In the northern sector of the Araçuaí orogen, the sandstone-pelite succession of the pre-glacial Rio Peixe Bravo Formation is covered by the Nova Aurora Formation, the glaciomarine unit rich in diamictite and Fe-rich diamictite, with minor graded sandstone and rare pelite. The Nova Aurora Formation is covered by the sandstone-pelite package of the Upper Chapada Acauã Formation. The pre-glacial and glaciogenic successions record the continental rift to transitional stages of the Macaúbas basin. The post-glacial succession represents proximal and distal passive margin to ocean floor environments. The Serra do Catuni Formation seems to be a proximal glaciomarine equivalent of the Jequitaí glacio-terrestrial deposits located on the São Francisco craton.