Correlação bioestratigráfica e paleoecológica de foraminíferos cenozóicos das Formações Marajó e Pirabas, Nordeste do Estado do Pará, Brasil

Abstract

Previous studies have re-evaluated stratigraphic and geophysical aspects of the sedimentary sequences of the east coast in the northeast of Pará state, reinterpreting the geological limits of the Marajó Basin and the Bragantina Platform, structures separated by the Vigia- Castanhal fault. These geotectonic compartments demonstrate the influence of the major transgressive event that occurred globally at the beginning of the Neogene and the intervention of the increased inflow from the Andean transcontinental cratonic drainage of the Amazon River on the development of the Bragantina Platform marine carbonate sequences from the Pirabas Formation (Oligo-middle Miocene) and the expressive siliciclastic-carbonate sedimentation of the Marajó Formation developed in the post-rift phase at the Marajó Basin. The two study sites Inhangapi (Marajó Formation) and Vigia (Pirabas Formation) are located near the Vigia-Castanhal trough and correspond to the boundary between the Marajó Basin and the Bragantina Platform respectively. This study aims at correlating biostratigraphically the paleoenvironmental conditions and paleoecologies based on qualitative and quantitative multivariate analysis, foraminifera association analysis by cluster grouping and paleodepth measurement with P/B ratio; carried out according to taxonomic classification of benthic foraminifera following specific contributions. The fossiliferous contents of these formations present a great similarity and diversity in the benthic hyaline microforaminifera that occur in both siliciclastic and calcareous depositional environments. These habitats have been colonized by a diverse and abundant benthic life that indicate shallow, warm, good circulation, and oxygenation in the transitional marine zone. Thus confirming that these two Cenozoic sedimentary units present different lithologies and depositional environments, the Marajó Formation being generated in a dynamic, suboxic, variable salinity, restricted marginal marine environment and marine incursions confirmed by the abundance of species such as Cribroelphidium williamsoni, Ammonia tepida and A. beccarii; and the Pirabas Formation was interpreted as a brackish marine marginal environment and oxic of middle neritic platform with abundance of the species Cibicides subhaidingerii and Cassidulina laevigata. These two localities maintain micropaleontological silimarities, confirmed by the presence of species such as Hanzawaia mantaensis, C. pachyderma, Uvigerina peregrina and Lobulata lobulata which converts them into chrono-correlative units.