The role of the relief dynamics in duricrusts evolution on Conceição River valley, Quadrilátero Ferrífero – MG

Abstract

Petrological studies using macromorphological, micromorphological, mineralogical and microchemical analyzes were performed to identify possible faciological variations of duricrusts in the different fluvial depositional levels of the Conceição River valley, Quadrilátero Ferrífero, Minas Gerais, and to understand its relation with the relief. Its position in the landscape suggests that these are the youngest duricrust of the Quadrilátero Ferrifero, and that its formation proves the dynamics of formation and transformation of weathering mantles in this important geological-geomorphological domain of Brazil. Previous research has revealed the existence of cemented levels interspersed with fine sediments and called them conglomeratic duricrusts. The results found here reiterate this denomination and clarify that the compositional variation of the cement allows identifying three distinct facies: F1 – aluminous duricrust; F2 – iron-aluminous duricrust and F3 – ferruginous duricrust. All types (especially F1 and F2) occur at the highest depositional level, and in the other levels only type F3 was identified. Microstructural organizations suggest genetic relationships between the facies. Old levels of iron-aluminous duricrust have undergone deferruginization, remobilizing the iron and concentrating aluminum, forming the type F1. As these are located at the highest fluvial level, the variety of facies can be used as an important indicator of the landscape evolution, characterizing a chronosequence.