Análise de fácies e proveniência sedimentar da formação capacete (Grupo Mata da Corda) na região sudoeste da bacia Sanfranciscana, Coromandel, Minas Gerais

Abstract

The Mata da Corda Group, Upper Cretaceous of the Sanfranciscana basin, is formed by the Patos and Capacete formations, which occur laterally interdigitated. The Patos Formation is composed of mafic-ultramafic alkaline volcanic rocks with effusive and explosive nature. The Capacete Formation is usually interpreted to consist essentially of epiclastic sedimentary rocks derived from reworking of the volcanic rocks of the Patos Formation. In the Coromandel region, west of the state of Minas Gerais, the Capacete Formation comprises deposits attributed to sedimentation in braided and meandering fluvial systems. The current paleogeographic model applied to this unit, which does not cover the area studied, suggests that the source-areas are in the south, in the region influenced by the uplift of the Alto Panaraíba Arch. This work, based on facies analysis (1:20 scale), paleocurrent measurements, Gazzi-Dickinson modal counting methos, and data available in the literature, presents a new paleogeographic model for the southwestern region of the Sanfranciscana Basin. The lithofacies described are consistent with previous studies and are evidence of a fluvial braided depositional system. However, paleocurrents measured on through and planar cross-stratification of sandstones from the Coromandel region indicate a dominant paleoflow toward the SE, with source-areas to the northwest of the depositional site. The modal detrital composition of the Capacete sandstones in the study area suggests source-areas in a recycled orogenic belt, in addition to a small contribution from volcanic rocks. Integration of paleocurrents and modal count data indicated that several units of the Brasília Belt, inclunding the mesoproterozoic orthogneisses of the Jurubatuba Suite and the neoproterozoic sedimentary rocks of the Araxá, Canastra, and Ibiá groups, with a small contribution of sediments from the neocretaceous volcanic rocks of the Patos Formation, acted as source-areas of the Capacete Formation during the Late Cretaceous time. Such rivers would have originated in a graben with N60-70W direction, parallel to the major axis of the Alto Paranaiba Arch.