Petrografia das Fácies Evaporíticas Sulfatadas do Membro Ipubi, Formação Santana (Bacia do Araripe)

Abstract

The Ipubi member of the Santana Formation (Araripe Basin) is a sulfated evaporite succession composed of gypsum and anhydrite of Aptian age, thus, it is chronocorrelated to the Brazilian Margin Salt Phase, when thick layers of salts accumulated. It is common in sulphate evaporites the variation between primary facies, which indicate the depositional features, and secondary facies, indicatives of recrystallization by diagenetic processes. This arrangement of facies is widely observed in the Ipubi Member, and it is due to a notable diagenesis, directly related with the basin evolution. Due to this situation, the present work aims through the petrographic characterization of these rocks to identify the different facies and to understand part of the diagenetic processes. In total, the 23 thins sections and 37 hand samples analysed indicated the occurrence of at least five facies; being two primary facies: prismatic gypsum and nodular anhydrite; and, three secondary facies: porphyroblastic gypsum, alabasterine gypsum and satin spar. After the identification, the different facies were organized according to the diagenetic stages, and from it, it was observed that the evaporites reflect, albeit locally, the regional processes that prevailed in the basin.