The Maranhão Basin, located in the N-NE region of Brazil, mainly in the states of Maranhão and Piauí, covers an area of approximately 600,000 km2. This basin had its framework formed in the Eopaleozoic, probably as a consequence of the collision between the Amazon and Brasiliana platforms, being considered of the intracratonic type or simple interior of the IS type. The sedimentary column of the Maranhão Basin is composed mostly of Silurian to Cretaceous rocks, with a thin Tertiary and Quaternary cover. The Piauí and Pedra de Fogo Formations represent the Permocarboniferous of this sedimentary column. The lithofaciological characterization, determined by means of drill cores in the two formations, was developed in several vertical profiles. The data obtained, compared to those in the literature, made it possible to define the various depositional environments. The sediments of the Piauí Formation can be arbitrarily divided into two members (Lower and Upper). The Lower is predominantly made up of coarse to very fine sandstones, with intercalations of shales and siltstones and rare levels of conglomerates. The Upper Member is composed of medium to very fine sandstones, with intercalations of carbonates, shales and siltstones, and subordinate levels of flint and evaporites being common. This Formation has an average thickness of 260 meters, being thicker in the central part of the Basin. Its lower contact with the Poti Formation, of the Lower Carboniferous, is discordant, and the upper one with the Pedra de Fogo Formation is gradual. These sediments belong to a desert system, with a brief marine transgression. Palynological analyzes of samples from the 1-MD-1MA well of the Piauí Formation show a palynological association constituted by the following genera: Puncttatisporites sp., Virkkipollenites cf. obscurus, Apiculatisporis sp. And Patonieisporites ap. This palynological association confirms the upper carboniferous age for the Piauí Formation. The Pedra de Fogo Formation is divided into three members (lower, middle and upper) with no formal stratigraphic connotation. The Lower Member consists of pelitic (siltite/shale), carbonate and evaporitic rocks, with less frequent contributions of flint and sandstones. It has an average thickness of around 45 meters. The Middle Member is characterized by a cyclic succession of siltstones, shales, sandstones and sometimes thick flint layers. Its thickness increases towards the center of the Basin, measuring on average about 44 meters. The Upper Member is characterized by sequences of siltstones, shales, carbonates and silexites. Subordinately, there are evaporites and sandstones. An average thickness of 58 meters is estimated, being thicker towards the west of the Basin.
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