Contexto estratigráfico e minerais pesados das unidades sedimentares cretácea e neógena aflorantes na Amazônia central

Abstract

Along the Solimões-Amazonas river system, between the Manacapuru and Uatumã tributaries (Central Amazon), siliciclastic rocks of the Javari Group outcrop, comprising the Cretaceous deposits of the Alter do Chão Formation and Neogenes of the Novo Remanso Formation, characteristic of a fluvial depositional paleoenvironment. They exhibit the best exposures in the municipalities of Manaus, Iranduba, Manacapuru, Novo Airão, Careiro Castanho, Itacoatiara, Beruri, and Presidente Figueiredo, where it is possible to visualize the irregular and discordant contact between the formations, defined mainly by well-developed lateritic paleosol. Although the individualization between formations is difficult due to the similarity of sedimentary facies, the use of heavy minerals integrated with palynological and geochronological data from paleosurfaces has proved to be an important tool in the elaboration of the regional stratigraphic framework. The Cretaceous unit is composed of an ultrastable assemblage with zircon, tourmaline, and rutile grains (ZTR index) and the neogenous unit presents an ultrastable to unstable assemblage with ZTR grains, in addition to sillimanite, staurolite, kyanite, epidote, apatite, topaz, amphibole (hornblende) and, less frequently, garnet. Mineralogical data could be associated with distinct source areas of the Amazon Craton, which were reworked during the implementation of the Cretaceous and Neogene drainage paleosystems in the Amazon Basin, which migrated west and east, respectively.