Wave-modified deposits of Pastos Bons Formation are interpreted as lacustrine system. This system was fed by fluvial channels, which constituted a flysch-like delta front. Subsiding areas controlled the implantation of lakes in southeast of Parnaíba Basin. Diminishing of salinity and aridity enhanced biological activity in Parnaíba Basin. Pastos Bons formation evidences the climatic attenuation in west Gondwana.