The Permian Pedra de Fogo Formation, which belongs to the Balsas Group of the Parnaíba
Basin, northern Brazil, is characterized a siliciclastic-carbonate succession with expressive
chert content, rare stromatolites and fossils of animals and plants, especially silicified trunks,
mainly of the Psaronius genus. In order to emprove the stratigraphic and paleoenvironmental
knowledgement of the upper portion of the Pedra de Fogo Formation, outcrop-basedm facies
analysis was carried out in the Filadélfia region, State of Tocantins, Southwestern Parnaíba
Basin. This study allowed the definition of a 100 m thick siliciclastic succession with
subordinate occurrences of carbonate and evaporites. Twenty-five sedimentary facies grouped
into six facies associations (FA) were identified: FA1-Lacustrine with ephemeral river
deposits; FA2- Storm wave-influenced lake deposits; FA3-Continental sabkha deposits; FA4-
Central lake deposits; FA5-Dune field deposits; and AF6-Lake/oasis deposits with inunditos.
These associations indicate that during Permian, an extensive lacustrine system developed
with adjacent dune fields and continental sabkha, as well as with contributions from
ephemeral rivers. Which when debauching into the lakes provide the formation of suspension
lobes and sheet flows (FA1). Sabkha plains (FA3) were formed in the marginal portions of the
lake, eventually influenced by storm waves (FA2), while the central zone was site of intense
pelitic deposition (FA4). The low supply of wind-blocon sand led to the formation of
restricted dune fields (FA5) with development of interdune lakes (oasis), where giant ferns,
sporadically flooded by ephemeral rivers (FA6). The predominanc of smectite and the lack of
kaolinite as well as the ocorrence of evaporites in the Association AF3 support the facies data
that the apper part of the Pedra de Fogo Formation was laid during a hot and arid climate.
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