Ambiente de sedimentação e análise petrográfica das rochas carbonáticas da formação pedra de fogo – Palestina-PA

Abstract

The carbonate rocks that outcrop in the Palestina do Pará city belong to the context of the western edge of the Parnaíba basin, the northern region of Brazil. The scientific works are few on the Parnaíba Basin with a focus in the Pedra de Fogo Formation in this region. Previous works carried through the Pedra de Fogo Formation had interpreted for the depositional environment as neritic-shallow to coastal with sabkha plains under influence of storm, fluvialdeltaic, lagoon/fluvial with marine/wind contribution. The faciological analysis carried out in the area allowed to determine the paleoenvironment of the upper portion of the Pedra de Fogo Formation from Permian age. The outcrops studied conceived a succession of approximately 4 meters in the profile 1 and 3 meters in the profile 2 is predominantly carbonated with siliciclastics, where two carbonaceous facies were compiled in three facies associations of (AFA) margin; (AFB) transition margin-center; and (AFC) Center. These associations suggest a lacustrine system that developed during the Permian period influenced by arid climate. The inflow of siliciclastic sediments on the lake provided the generation calcilutites at the lake margin (AFA). With the phases of expansion and contraction that occurred in the lake, it has provided the intercalation of mudstone plated and mudstone massive facies (AFB). In the central portion of the lake has developed intense carbonate precipitation that prevailed until the time when the water depth began to decline (AFC).