Depósitos sedimentares neoproterozoicos do Grupo Tucuruí - Cinturão Araguaia, Nordeste do Pará

Abstract

The Tucuruí Group of Neoproterozoic age outcrops in Tucuruí region, northeastern of Pará state, along with the transition between the Amazonian Craton and Araguaia Belt. The group is defined by a volcano-sedimentary sequence containing basaltic flows and diabase sill intrusions interbedded with siliciclastics deposits. The Tucuruí thrust fault override these sets rocky westward resulting in shearing, fracturing and fluid percolation in these rocks. The siliciclastic deposits consist of amalgamated subarkoses and siltstones, whose layers are oriented NNE-SSW direction with low dip to SE. In addition presenting coarsening and thickening upward. In this investigation were recognized two sedimentary facies associations: Deposits of Shoreface and Coastal Tempestites Face. This association suggests easy transport processes and sedimentation linked to a shallow marine environment, following the foreshore zone to zone shoreface under influence of wave storm. The petrographic analysis revealed the compositional and textural immaturity of arkosean sandstone and siltstone indicating nearby source area of provenance of mafic to intermediate igneous rocks. The sequence was subject to the mesodiagenetic sedimentary conditions. Thus, the siliciclastic deposits of Tucuruí Group represent the portion of a preserved segment influenced by coastal storm waves in a rift basin or foreland with nearby source area, composed of igneous rocks with strong relief, and marked predominantly by physical weathering. Basaltic volcanic flows occurred during the evolution of this basin.