Palinologia da Formação Pirabas, nos municípios de Primavera e Salinópolis, nordeste do estado do Pará, Brasil

Abstract

During the Paleogene - Neogene transition, the Amazon coast (Brazil) presented very low rates of sedimentation and influx of siliciclastic sediments supplied by an ancient river basin, which allowed the formation of extensive and thick carbonate deposit. According to the development of Amazon fan in the upper Miocene, these deposits may have represented the last stage of carbonate sedimentation in transitional environments of the Amazon coast. The integration of facies and pollen analysis of a drill hole from Primavera/PA (FPR-160 core) and reassessment of pollen systematic of Cunha (2013) from an outcrop in Salinopólis/PA, allowed the identification of a lagoon connected to a shallow marine platform formed between the upper Oligocene and lower Miocene. The occurrence of Retibrevitricolporites grandis in FPR-160 core in the basal portion of the core, which is just above the crystalline basement rocks, provided a maximum age restricted to the upper Oligocene for the base of the formation Pirabas. The presence of Retitrescolpites irregularis, Psilatricolporites crassoexinatus and Retibrevitricolporites grandis together with the absence of Zonocostites ramonae and Deltoidospora adriennis may indicate that there was considerable continental influence on the deposits or occurrence of a marine environment with restricted mangrove areas. The occurrence of Mauritiidites franciscoi, P. crassoexinatus, R. irregularis, Malvacipolloides maristellae and Zonocostites ramonae in the outcrop in Salinopólis/PA, suggests lower Miocene age to the top of this unit, interpreted as a lagoon bordered palaeoenvironment by mangrove vegetation.