The Pirabas Formation occurs in the physiographic zones of Salgado and Bragantina, northeast region of Pará state, in an extensive and scattered outcrops, most expressive at Capanema, Salinópolis and Maracanã areas, and others less expressive localities that are disappearing due to urban expansion or by quaternary sedimentation cover. This research deals a detailed micropaleontological analysis in the occurrence of district of Japerica, municipality of São João de Pirabas, a restricted, highly weathered outcrop with macrofossils absents. This study reveals a microfaunistic association characterized by little abundance and apparent generic and specific diversity, consisting of nine genera of bryozoans, in addition to bivalves, echinoids, ophiuroids and crinoids, as well as rare ostracods and gastropods. The paleoenvironmental interpretations suggest an eutrophic and shallow marine environment with agitated, oxygenated, warm waters with high disponibility of calcium carbonate. The rich and varied microfossiliferous content of this same lithofacies in better represented occurrences of the Pirabas Formation, suggests changes in the original taxonomic composition due to diagenetic processes and continuous action of physical and chemical weathering on the rocks (leaching, dissolution and recrystallization processes) causing fragmentation and great destruction of a majority of bioclasts and poor preservation quality of the present taxa, which made it difficult to recognize diagnostic morphological features.
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