Fácies e associação de fácies dos depósitos sedimentares da Formação Ipixuna, nos arredores da cidade de Ipixuna do Pará, Sub-Bacia de Cametá, norte do Brasil

Abstract

The studied sedimentary deposits are distributed around the city of Ipixuna do Pará, along the Belém-Brasília (BR 010) road, located in the northeastern of the state of Pará. These deposits belongs to Ipixuna Formation, margin of Cametá Sub-Basin, Graben System of Marajó. Historically, the Ipixuna Formation have been studied due to the occurrence of associated kaolin deposits. However, there are still gaps in our understanding of the geology/sedimentology that allow the understanding of the Cretaceous sedimentation episodes which acted in filling the basins of Graben Marajó. The first sedimentological studies conducted in the study area attributed genesis related to the occurrence of fluviallacustrine channels in the region. However, new evidences revealed the fluvial-estuarine nature of these packages. The present study corroborates the recent studies in the area. The facies mapping allowed the identification of one facies Association subdivided into four subassociations: Sub-association: Center channel, Sub-association Floodplain, Sub-association Point bar e Sub-association Longitudinal sand bar, composed of polymictic conglomerates, friable sandstones to kaolin-rich sedimentary structures such as with tabular cross-bedding and trough cross-bedding, festonate cross-bedding with foresets covered by massive and laminated films of clay, Siltstones and Mudstones, pelites with Heterolitic Inclined Bedding, containing fossil traces of Skolithos facies. The facies analysis suggests that intergradative processes assigned to tidal estuary complex environments meandering river channels, in the context of tidal influence activities.