Caracterização mineralógica por difratometria de raios-x de arenitos da Formação Capacete (Cretáceo Superior da Bacia Sanfranciscana) em Coromandel, Minas Gerais

Abstract

The Capacete Formation, Upper Cretaceous of the Sanfranciscana Basin, consists mainly of pelite, sandstone, and conglomerate deposited in braided and meandering river systems. The aim of this work was the mineralogical characterization of the sedimentary rocks of the Capacete Formation in Coromandel, state of Minas Gerais, Brazil, by X-ray diffraction (XRD) analyzes. The mineralogical composition of the ten samples analyzed is relatively uniform. The minerals identified were quartz, muscovite, illite, orthoclase and kaolinite. The combination of facies analysis, paleocurrent and modal count data with the XRD data obtained here confirms and refines the understanding of the sedimentary provenance of the Capacete Formation. The mineralogy identified in the sandstones and conglomerates suggests that the igneous and metamorphic rocks of the Brasília Belt were the main source of the sediments of the Capacete Formation during the Late Cretaceous. In this sense, the quartz and muscovite grains most likely originate from the phyllites and quartzites of the Rio Verde Formation of the Ibiá Group and the schists and quartzites of the Araxá Group. The orthoclase grains are interpreted as originating from the metagranites and metatonalites of the Jurubatuba Suite. The identified clay minerals are interpreted as the product of chemical weathering of feldspars and muscovite. The minerals identified by XRD suggest source areas in the N-NW from a recycled orogenic belt.