CARACTERIZAÇÃO MINERALÓGICA DOS MINERAIS PESADOS DA UNIDADE SEDIMENTAR NEÓGENA AFLORANTE NA ZONA DE CONFLUÊNCIA DOS RIOS NEGRO E SOLIMÕES, AMAZÔNIA CENTRAL

Abstract

The present study emphasizes the use of heavy minerals in the mineralogical characterization of the Neogene sedimentary unit informally called the Novo Remanso Formation, outcropping on the banks of the Negro, Solimões, and Uatumã rivers (Central Amazonia). In the last decade, sedimentary facies and palynology studies have individualized this formation and positioned it unconformably above the Cretaceous unit (Alter do Chão Formation) of the Purus Group in the Amazon Basin. The heavy mineral methodology has proven to be an efficacious tool to distinguish these formations that make up much of the relief in this part of the Amazon, especially in places where the contact relationship is not evident and/or hidden. Another critical factor that makes it challenging to individualize the outcrop formations is the similarity of the sedimentary facies, which indicates a fluvial depositional environment that sometimes still appears to be modified by overlying pedogenetic processes. The mineralogical data obtained in this study indicate that the Neogene sedimentary unit has an ultrastable to an unstable assemblage of heavy minerals, with a variety of ZTR grains (zircon, tourmaline, and rutile), in addition to sillimanite, staurolite, kyanite, epidote, apatite, topaz, amphibole (hornblende), and, less commonly, garnet. This mineralogical signature can serve as a standard for paleogeographic studies and sedimentary provenance that relate the Novo Remanso Formation deposition to the Neogene implementation of the Amazonas Basin drainage paleosystem, which migrated from west to east.