Conodonts of chesterian age (lower carboniferous) from Amazonas Basin

Abstract

Conodonts characteristic of Chesterian age (Lower Carboniferous) were collected fonn the Tapajós River outcrops, in Pará State at the base of the Itaituba Fonnation, Amazon Basin. The identified species are Gnathodus bilineatus, Lochriea mononodosa, Gnathodus girtyi. These conodonts porvide good cross coverage for improved intercontinental correlation near the Mississipian-Pennsylvanian boundary. The presence of these chesterian fonns along the Tapajós River constitutes important tools to the stratigraphic correlation of Amazon Basin and other basins. These fonns, absents in the adjacents sediments to the Puros Arch, provide new ideas about the first transgressions in this basin. It is proposed that this marine transgression couldbe ingressed through a regional northeast-southwest structuraJ low crossing the outcroping area, and associated to tectonism originated form Early Hercinien Orogenic pulses together with the Purus Arch.