Navegando por Assunto "Neogeno"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Famílias hyriidae e mycetopodidae (Mollusca:Bivalvia) da Formação Solimões (Mio-Plioceno) bacia do Solimões, AM, Brasil: taxonomia, inferências paleobiogeográficas e paleoambientais.
(Universidade Federal do Pará, 2024-06-16) ARAÚJO, Lorena Lisboa; RAMOS, Maria Inês Feijó; http://lattes.cnpq.br/4546620118003936; https://orcid.org/0000-0003-0276-0575
The Solimões Formation, situated in western Amazonia, represents the Neogene sedimentary sequence from Solimões Basin. Its is correlated to Pebas Formation in Peru and is well known for its abundant and rich fossil content, including mollusks. Research on fossil mollusks bivalves from this unit began in the 19th century, with the Gabb (1868). These organisms have calcareous bivalve shell that allow their preservation, making them valuable tools in paleoecological, paleoenvironmental, biostratigraphy and paleogeography studies. Despite the abundance and diversity of this group in western Amazonia, in Brazil there is only few studies conducted. Therefore, the present study aimed the taxonomic identification of bivalve mollusks belonging to the families Hyriidae and Mycetopodidae and to contribute in paleoenvironmental and paleoecologic interpretations, as well as the paleobiogeographic distribution of the identified fauna. The study material comprised 200 samples collected from sedimentary banks along the Jurua and Javari rivers, near Eirunepé and Atalaia do Norte towns, Amazonas State, Brazil. The taxonomic analyses allowed the identification of three genera (Castalia, Diplodon, and Prisodon) from the family Hyriidae, and one genus (Haasica) from the family Mycetopodidae. The fossil assemblage consists exclusively of freshwater taxa, indicating lacustrine and fluvial environments during the upper Miocene in the study area. The genus Castalia exhibits a wide geographical distribution, primarily in South America, with its oldest records dating to the Cretaceous. Its absence in the Paleogene may be attributed to limited studies of this period in Brazil, which focused mainly on marine basins. Meanwhile, records of the genus Diplodon span from the Jurassic to the upper Miocene. For the first time, fossil evidence of both genus Prisodon and Haasica was identified in the Miocene.
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.
Acesso aberto (Open Access)
Strontium isotope stratigraphy of the Pelotas Basin
(2014-03) ZERFASS, Geise de Santana dos Anjos; CHEMALE JUNIOR, Farid; MOURA, Candido Augusto Veloso; COSTA, Karen Badaraco; KAWASHITA, Koji
Strontium isotope data were obtained from foraminifera shells of the Pelotas Basin Tertiary deposits to facilitate the refinement of the chronostratigraphic framework of this section. This represents the first approach to the acquisition of numerical ages for these strata. Strontium isotope stratigraphy allowed the identification of eight depositional hiatuses in the Eocene-Pliocene section, here classified as disconformities and a condensed section. The reconnaissance of depositional gaps based on confident age assignments represents an important advance considering the remarkably low chronostratigraphic resolution in the Cenozoic section of the Pelotas Basin. The recognition of hiatuses that match hiatuses is based on biostratigraphic data, as well as on global events. Furthermore, a substantial increase in the sedimentation rate of the upper Miocene section was identified. Paleotemperature and productivity trends were identified based on oxygen and carbon isotope data from the Oligocene-Miocene section, which are coherent with worldwide events, indicating the environmental conditions during sedimentation.