The Parnaíba sedimentary basin western margin geology in the State of Pará, Brazil, indicates that the present basin margin is of a tectonic origin and not its original depositional limit. The Paleozoic section bearing fine sediments are strongly faulted and is covered by an extensive Cenozoic sedimentation probably the last period of tectonic reactivation. To the north, parallel to the Tocantins river, a thick Quaternary sedimentation covers all the preceding formations reaching colossal thicknesses at the mouth of the Amazon river.
