Caracterização textural e mineralógica preliminar das barras arenosas e manguezais do estuário do rio manguezais do estado do Pará

Abstract

The Mojuim River flows into the Marajó Bay, forming a tidally dominated estuary composed of several depositional environments (sandy and muddy tidal flats, estuarine bars and islands colonized by mangroves). These environments are composed of unconsolidated sediments, whose textural, mineralogical, and aprovenience characteristics are the fundamental objective of this work. Samples were collected using a dredge, Vibracore system and a mud auger, and later submitted to lithological and textural description, and laboratory processing for grain size and classic mineralogical analyses (heavy minerals and X-ray diffraction). The mangroves are composed of essentially muddy sediments (very low silt content) bioturbated, with oxidation zones ranging from 50 to 70cm. The estuarine bars are composed of medium to fine, light gray, moderately selected, very platicuretic sand, with approximately symmetric distribution and composed predominantly of subangular to subrounded grains of quartz, epidote, tourmaline, zircon, tremolite, staurolite, basaltic homblende, and cyanite. The presence of microfossils (foraminifera) was also recorded. The sedimentological parameters analyzed (degree of rounding and selection), the low ZTR index and the presence of unstable minerals indicate the textural and mineralogical immaturity of the estuarine bar sediments. The source of these sediments is associated with the Barrier Formation, over which the Mojuim River has much of its course laid down. However, the presence of microfossils may indicate another source area (platform sediments and/or Pirabas Formation).