Neoproterozoic glacial and gravitational sedimentation on a continental rifted margin: The Jequitaı́–Macaúbas sequence (Minas Gerais, Brazil)

This paper is a contribution to the knowledge of the sedimentation of Neoproterozoic sequences, known as the Jequitaı́ Formation and Macaúbas Group. These sequences are present along the transitional zone between the São Francisco Craton and the Brasiliano (≌600 Ma) Araçuaı́ fold belt in Minas Gerais, Brazil. A sedimentological study of these Neoproterozoic sequences enables us to distinguish between true continental and marine glacial facies and glacial material reworked by various subaqueous gravitational processes. The cratonic Jequitaı́ Formation consists of massive and stratified diamictites up to 100 m thick. This diamictite association is tentatively interpreted as glaciomarine in origin. It continues eastward, in the Araçuaı́ fold belt, as the metasedimentary Macaúbas Group, which is composed of metadiamictites, quartzites and schists from 5–12(?)km thick. The Macaúbas Group consists of resedimented glacial material deposited by subaqueous debris flows and turbidity currents. A depositional model is proposed for the Jequitaı́–Macaúbas glacial/gravitational sequence. From west to east, a glaciomarine sequence, possibly deposited from an ice-sheet and slightly reworked by gravitational processes, was reworked along the São Francisco cratonic border and generated a slope apron system made up of diamictites associated with turbidites and rhythmites.