Navegando por Assunto "Neogene"

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Acesso aberto (Open Access)
Flora e fauna do neógeno das áreas de manguezais de lagoas costeiras da plataforma equatorial do Brasil: processo de piritização
(Universidade Federal do Pará, 2021-04-02) MATA, Giovanni Alvaro Teixeira da; AGUILERA SOCORRO, Orangel Antonio; http://lattes.cnpq.br/5854051483674293; https://orcid.org/0000-0003-4418-8351
The carbonate-siliciclastic rocks from the early to middle Miocene Pirabas Formation in the equatorial margin of Brazil show a brackish ecofacies of mangrove and coastal lagoons paleoenvironments under tidal influence. The studied section has dark mudstone at the top, characterized by a microbial methanogenesis zone where pyritized trunks, leaves, micro- and macrofossils, and trace fossils, have been investigated. The petrographic characterization and crystallographic analyses distinguish mostly framboids crystal for trunk fragments to the octahedric and cubic crystals from invertebrate shells. The geochemistry analyzes revealed that Fe and S are concentrated both in the fossiliferous content of invertebrate constituents and in the matrix that hosts the trunk, while the other elements are mainly linked to invertebrates. The preferential distribution of these elements is in accordance with the presence of FeS2 compounds replacing fossils, reflecting the anoxic and reducing conditions of the environment. The pyrite-rich lithostratigraphic section was deposited in a shallow water environment, where pyrite mineralization was developed during the early diagenetic stage under anoxic conditions, plenty of organic matter, warm and mixohaline water. The integration of faciological, stratigraphic and chemical data from the carbonate deposits of the Pirabas Formation, in addition to reconstructing the stratigraphic behavior of these units in the period studied, would also assist in understanding the paleoenvironmental and paleogeographic changes of the Bragantina Platform and its possible relationship with global events.
Acesso aberto (Open Access)
O Neógeno e Pleistoceno da Amazônia Central: Palinoestratigrafia, Paleoambiente e relação com os eventos evolutivos do Rio Amazonas
(Universidade Federal do Pará, 2021-03-19) LIMA JÚNIOR, Walmir de Jesus Sousa; JARAMILLO, Carlos Alberto; NOGUEIRA, Afonso César Rodrigues; http://lattes.cnpq.br/8867836268820998
Outcrop-based facies analysis of 25 m-thick Neogene succession was carried out in the Eastern Solimões Basin, Central Amazonia. The Miocene Solimões Formation includes lake/overbank, suspended-load meandering fluvial channel with subdelta crevasse, and flood plain/crevasse splay deposits, confirming the previously interpreted Pebas-Solimões megawetland system. The Upper Pleistocene Içá Formation unconformably overlies the Solimões Formation and comprises mixed load to bedload meandering fluvial channel and floodplain deposits. The Solimões Formation's palynostratigraphy was carried in this exposed succession and a drill core (196-291 m), generally in organic matter-rich mudrock. The occurrence of exclusively continental fossils associated with phytoclasts and freshwater algae such as Ovoidites confirm the wetland setting restricted to Western Amazonia. Monoporopollenites annuulatus and other grasses indicate an oscillation between shrub and tree phases linked to dry and humid interval fluctuations. The upper Miocene-Pliocene ages for the Solimões Formation obtained since amplitudes zones identified mainly Crassoretitriletes vanraadshovenii, Echiperiporites akanthos, Echiperiporites stelae, Fenestrites spinosus, Psilastephanoporites tesseroporus, Grimsdalea magnaclavata, and Alnipollenites verus. The first appearance of Alnipollenites verus is modified for the Miocene. Reworked palynomorphs found in this succession indicate autocyclic processes related to the environmental dynamic, while acritarchs indicate erosion of Paleozoic source areas. The Andean tectonics affected Central Amazonia dramatically, causing the progressive uplift of the Solimões Basin and the emergence and demise of the Pebas-Solimões mega-wetland succession. This progradation event was amplified by the expressive sea-level fall in the middle-Tortonian (11-8 Ma), resulting in the Andean Amazon River's onset. The generated unconformity resulted in a gap and bypass sediment of ~ 9,5 Ma. Only in the Late Pleistocene, the Solimões Basin subsided, causing the implantation of a mixed- to bedload meandering system that represents the sedimentation restart of the Amazon River in the Central Amazonia.