Minerais Pesados dos Sedimentos de Fundo do Estuário do Rio Marapanim

Abstract

Heavy minerals are important indicators of sedimentary processes that help in the interpretation of the depositional history of sediments, making it possible to identify their source-area for a given environment. The Marapanim River estuary, located on the northeast coast of Pará, was chosen as a working area for a study of the characterization and provenance of the estuarine bottom sediments, through the analysis of heavy minerals. The main objective was to study the heavy minerals, identifying and quantifying their distribution along the estuary, to later compare them with the sediments that constitute the mangroves of this region, as well as with the sediments of the probable source area (Formação Barreiras). Fifty sediment samples were collected and submitted to grain size separation and grain counting on slides using a petrographic microscope. Some grains were observed and analyzed using a scanning electron microscope (SEM). The main non-opaque heavy minerals occurring in the background sediments are: colorless, brown and pink zircon, euhedral, subrounded and rounded; green, yellowish-brown and brown tourmaline, prismatic, subrounded and rounded; light yellow and reddish-yellow staurolite, angular and subrounded; and subhedral cyanite. Minerals that occur in smaller quantities are rutile and sillimanite. The study indicated that the estuarine bottom deposits make up an average of 38% zircon, 20% tourmaline, 32% staurollta and 10% cyanite among the heavy minerals. Data on provenance are still limited, but the results show that these minerals partially resemble the assembly of sediments of the mudflat mangrove plain, as well as the sediments of the Barrier Formation, in proportions and textural characteristics.