The Cretaceous Codó Formation exposed in the Central Parnaíba Basin was studied in outcrops and mines in the Pedreira Grossa Integral, Grajaú region, Estate of Maranhão. The integration of facies/microfacies and palynological analysis allowed to corroborate with previous interpretation to this unit and it also provide some paleoclimatic insights. Six sedimentary facies were identified and grouped into 2 facies associations of a lacustrine system: 1) wave-influenced central lake, formed by black shale, nodular gypsum, green shale and sandstone with wave-cross lamination, with nodular gypsite and rosete of gypsite; and 2) salt pans and sabkha, composed by fibrous/laminar gypsum, gypsum arenite, and chevron gypsite, acicular gypsite, mosaic gypsite, pseudonodular gypsite. Palynomorphs analysis indicated the absence of gymnosperms and abundance of angiosperm palynomorphs from Monoporopollenites, Retitricolporites and Stephanocolporites, Psilamonocolpites, Echitriporites, Retiperiporites genus, as well as Retitriletes fern. This assemblage suggests a wet environment with well-developed forests likely related to marginal zones of lakes or floodplain, unlike previous interpretation of arid climate to Codó Formation. The development of these research provided training in evaporitic rocks, also contributing to the development of similar sedimentary models of source and selant rock of Parnaíba Basin.
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