Papers by Rogério Oliveira Barbosa
O Arquipelago de Anavilhanas, localizado no baixo curso do Rio Negro, se desenvolveu sobre rochas... more O Arquipelago de Anavilhanas, localizado no baixo curso do Rio Negro, se desenvolveu sobre rochas siliciclasticas das formacoes Nhamunda (Paleozoico), Alter do Chao (Cretaceo) e Novo Remanso (Neogeno), sendo constituido por 2 unidades de terracos fluviais, o superior (TFS) e o inferior (TFI). Os terracos foram individualizados principalmente por meio de datacoes (LOE e C-14), que revelaram idades de 211.394 +/-29.300 anos AP a 69.988 +/- 8.860 anos AP para o TFS e de 2.558 +/- 87 anos AP a 368 +/- 145 anos AP para o TFI. O TFS esta localizado na margem esquerda do Rio Negro, posicionado em cotas entre 25 m a 40, sendo constituido por intercalacoes de camadas de areia e lama (silte e argila), que definem pares de estratificacao heterolitica inclinada relacionadas a migracao de barras laterais em um rio retilineo. A deposicao deste terraco esta relacionada ao grande aporte de sedimento mais grosseiro liberado por erosao durante o periodo de rebaixamento do nivel do mar. O TFI e repres...
Journal of South American Earth Sciences, 2017
The Amazonas fluvial system originates in the Andes and runs ca. 6700 km to the Atlantic Ocean, h... more The Amazonas fluvial system originates in the Andes and runs ca. 6700 km to the Atlantic Ocean, having as the main affluent the Negro River (second largest in water volume). The Amazonas transcontinental system has been dated to the late Miocene, but the timing of origin and evolutionary processes of its tributaries are still poorly understood. Negro River alluvial deposits have been dated to the middle to late Pleistocene. Recently, we studied a number of boreholes drilled for the building of a bridge at the lower course of the Negro River. A thin (centimetric) sedimentary deposit was found, laterally continuous for about 1800 m, unconformably overlaying middle Miocene strata and unconformably overlain by younger Quaternary deposits. This deposit consists predominantly of brownish-gray sandstones cemented by siderite and with subordinate mudstone and conglomerate beds. Palynological, granulometric, textural and mineralogical data suggest that the initial Negro River aggradation took place in the deep incised valley under anoxic conditions and subsequently along the floodplain, with efficient transport of mixed origin particles (Andean and Amazonic). Angiosperm leaves, wood and pollen are indicative of a tropical continental palaeoenvironment. A well preserved palynoflora that includes Alnipollenites verus, Grimsdalea magnaclavata and Paleosantalaceaepites cingulatus suggests a late Pliocene to early Pleistocene (Piacenzian to Gelasian) age for this unit, which was an age yet unrecorded in the Amazon Basin. These results indicate that by the late Pliocene-early Pleistocene, large scale river activity was occurring in Central Amazonia linking this region with the Andean headwaters, and therefore incompatible with Central Amazonia barriers like the Purus arch.
Uploads
Papers by Rogério Oliveira Barbosa