CONTEXTO ESTRATIGRÁFICO E ANÁLISE DE MINERAIS PESADOS DA MEGASEQUÊNCIA SEDIMENTAR CRETÁCEA-NEÓGENA AFLORANTE NA PORÇÃO OESTE DA BACIA DO AMAZONAS, AM

Stratigraphic context and heavy mineral analysis of the Cretaceous and Neogenous sedimentary units in the western portion of the Amazon Basin, AM

Abstract

In the western portion of the Amazon Basin, the Mesozoic-Cenozoic siliciclastic rocks megasequence of the Javari Group spring up, formed by the Alter do Chão and Novo Remanso formations, characteristic of fluvial depositional paleoenvironments. They exhibit the best exposures in Manaus, Iranduba, Manacapuru, Novo Airão, Careiro Castanho, Itacoatiara, Beruri, and Presidente Figueiredo municipalities where they are possible to visualize the discordant contact between the units despite the challenge in individualization due to the sedimentary facies’ similarity. Associated with palynological and regional paleosurface data, the application of the heavy minerals’ method has proved to be a crucial tool in defining the Cretaceous-Neogene stratigraphic framework in the western portion of the Amazon Basin owed to the defined mineralogical differences. While the Cretaceous unit is composed of an ultra-stable assemblage with zircon, tourmaline, and rutile grains (ZTR index), the Neogene one stands an ultra-stable to unstable assembly with ZTR grains, in addition to sillimanite, staurolite, kyanite, epidote, apatite, topaz, and hornblende. The differences observed were 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.