Análise faciológica dos evaporitos do membro Ipubi (Formação Santana) nas minas Pedra Branca e Conceição Preta, Município de Santana do Cariri, Ceará

Abstract

This present paper has as objective the faciologic description of the Ipubi member of the Santana Formation, in the Pedra Branca and Conceição Preta mines, the town of Santana do Cariri, setted in the Araripe Plateau, south portion of the Ceará state. The metodology used was the outsourcing of the mines estratigraphics sections and analisis of one hole poli with approximately 30 meters length. Was firstly identified in the work, three faciologic units: with gypsum-anhydrite, carbonatic-clay and anhydrita-gypsum compositions. In the section base occurs a anhydrite-gypsum, with micro-crystalline anhydrite altered to gypsum according to stratification plans and transversal fractures. Just above occurs a shale layer with thin and biomicritic (ostracodes) limestone intercalations, and fibered gypsum veins parallel to the bedding. Over covering these, occurs a thick gypsum layer compounded by micro- and macro-grained gypsum, presenting rare shale and cardonates lenses. While the complete section outcrops in the Conceição Preta mine, only the superior gypsum section outcrops in the Pedra Branca mine. Possibly, the anhydrite-gypsum transformation took place during a uprising of the groudwater which hydrated the anhydrite, so that facies is diagenetic, just like the gypsum-anhydrite facies is sin-depositional, by were progressive transformation of the gypsum into anhydrite. Meanwhile, the carbonate-clay facies corresponds a transition between a more tempered climate and a more dry and arid climate during the gypsum/anhydrite deposition time. About the deposit genetic model, there are no conclusive data to determinate the possible sedimentation environment.