The Gorutuba Formation: coastal to continental sedimentation on the eastern margin of Bambuí Basin (MG)

Abstract

In this study, we formally introduce the Gorutuba Formation, unit that encompasses the remaining coastal and continental records of the eastern margin of the Bambuí Basin, evolved during the Brasiliano/Pan-Africano Orogeny. In Minas Gerais, the Gorutuba Formation occurs in three main localities. In Jaíba and Colonial ridges, the unit shows a basal layer of breccia composed by clasts of limestone in arcosean matrix, recording the erosion and reworking of the underlying Jaíba Formation. Arcose occurs as layers and lenses within the breccia, and becomes the main rock to the top, where shows some lenses of ortoconglomerate. In Gorutuba and Rompe Gibão ridges, the unit shows the same stratigraphic pattern, but lies on the Serra da Saudade siltstones. In Buenópolis Sincline, on the other hand, arcosean sandstone with through cross stratification and conglomerate lenses lie on siltstones from Serra da Saudade Formation, lacking the basal breccia. The Gorutuba Formation records an uplift, exposure and erosion stage of the wide Bambuí marine platform. The basal breccia, which occurs in the northernmost areas, records an important unconformity, where the Jaíba carbonatic shelf was reworked by waves in response to the tectonic driven uplift. The increase of the sandstones to the top is associated to the gradual installation of a high-energy fluvial system, marking the clogging stage of the basin. The composition of the sandstones and the breccia’s matrix suggests the exhumation of granitic sources in the Araçuaí Orogen in this period.