Datação de Sedimentos Pós-Barreiras no Norte do Brasil: implicações paleogeográficas

Abstract

The Barreiras Formation exposed in the northeastern of the State of Pará, overlain by a variety of oxidized, light red to pale yellow strata, whose ages are presented, for the first time, in the present work. Based on dating methods applying optically stimulated luminescence (OSL) following the protocols MAR (Multiple Aliquot Regeneration) and SAR (Single Aliquot Regeneration) and, whenever possible, 14C, it was possible to conclude that the formation of these strata took place at the end of late Pleistocene to Holocene, with recorded LOE/MAR ages ranging from 430,000 (±60,000) to 3,400 (±400) yr BP. A comparison of OSL/MAR and OSL/SAR results showed good equivalence among values for the deposits with younger ages, and significant differences for deposits with relatively older ages. The fact that strata with older ages show evidence for deposition under sub-aqueous conditions led to conclude that the differences obtained herein is more likely due tothe cosmic radiation acquired during deposition in previous depositional sites. Taking into account the obtained ages, and integrating these data with information derived from previous publications, it can be concluded that the Post-Barreiras Sediments record deposition at the margin of a wide paleovalley, which display its main sedimentary record to the west of the study area