Navegando por Assunto "Micropaleontologia"

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Acesso aberto (Open Access)
Estudo paleontológico do limite oligoceno/mioceno nas formações Ilha de Santana e Pirabas nas bacias Pará-Maranhão e Barreirinhas na plataforma equatorial noroeste do Brasil.
(Universidade Federal do Pará, 2023-12-14) GUIMARÃES, Beatriz Teixeira; AGUILERA SOCORRO, Orangel Antonio; http://lattes.cnpq.br/5854051483674293; https://orcid.org/0000-0003-4418-8351
Sedimentary carbonate outcrops of the Pirabas Formation at the Bragantina Platform in North Brazil represent the exposed portion of the entire carbonate succession in the marine equatorial platform from the subsurface Ilha de Santana Formation (Cretaceous/Maastrichtian-Miocene/Aquitanian) in the Pará-Maranhão Basin and from the Formation Pirabas (Miocene/Aquitanian-Serravallian) in the Barreirinhas Basin, both from the Humberto de Campos Group. The transgressive deposit, flooding, and advance of the carbonate platform were investigated through the study of outcrops of the Pirabas Formation (type locality in the Ilha de Fortaleza, Pará state) and the analogous carbonate of the upper section of the Ilha de Santana Formation of the well-log 1- MAS-16-MA (510 to 660 meters below the seabed). The stratigraphic analyses were based on petrography, microCT, microfossil assemblages (foraminifers, ostracods, and bryozoans) and index species (Amphistegina, Archaias, Pyrgo, Quinqueloculina, Pirabasoporella, Nellia, Skylonia, and Alpheus), and biofacies approach. The boundary between the Ilha de Santana Formation (Aquitanian/Burdigalian at 510–660 m section of 1-MAS-16-MA) and the Pirabas Formation (Burdigalian/Serravallian at the Ilha de Fortaleza outcrop) suggests that shallow-water sedimentary facies are similar to those deposited in the marginal basins and marks the start of siliciclastic supplies to the inner platform and the reduction of coralline algal carbonate factories.
Acesso aberto (Open Access)
Taxonomia do gênero Cyprideis (crustacea; ostracoda), Formação Solimões (Mioceno), Bacia do Solimões, estado do Amazonas, Brasil.
(Universidade Federal do Pará, 2023-11-26) FERREIRA, Renato Rafael Martins; RAMOS, Maria Inês Feijó; http://lattes.cnpq.br/4546620118003936; https://orcid.org/0000-0003-0276-0575
Studies of Neogene ostracods from the western Amazonia region, began in 1979, mainly dealing with taxonomic identification, recording a vast, diverse, and endemic fauna, predominantly represented by the Cyprideis genus. This genus is euryhaline and adaptable to the most diverse environmental conditions, such as water salinity level, temperature, and oxygenation, presenting high ecophenotypic plasticity. Thus, the rapid adaptive response of the genus to bioevents, during the deposition of the Pebas System, in the Neogene, in the western region of the Amazonia, led to the development of peculiar morphological characteristics and high intraspecific variation, making it difficult to differentiate species of the genus within this system. Although several authors have studied the Cyprideis genus from the Neogene of Western Amazonia, the number of species is still underestimated. In that context, the present study aimed to survey and taxonomic refinement of the species of this genus, from different boreholes (1AS-1-AM, 1AS-4-AM, 1AS-8-AM, 1AS-32- AM, 1AS-33-AM and 1AS-36-AM) drilled in the western Amazon, west of the state of Amazonas. A total of 9353 valves were counted, in which 30 species and 8 genera of ostracods were identified. Out of these, 22 species belong to the Cyprideis and 8 belong to other genera (Cypria aqualica, Cytheridella danielopoli, ?Paracypris sp., Pellucistoma curupira, Penthesilenula olivencai, Perissocytheridea acuminata, Perissocytheridea ornellasae and Rhadinocytherura amazonensis). The species Cyprideis goeldiensis and Cyprideis javariensis are new and Cyprideis sp. 1 remains in open nomenclature. A new variation of the species Cyprideis matorae was identified and the species Cyprideis santaelenae, originally described for the Pebas Formation, is recorded here for the first time for the strata of the Solimões Formation. The presence of index species allowed the identification of four ostracod zones in core 1AS-32-AM (Cyprideis caraionae Zone, Cyprideis minipunctata Zone, Cyprideis cyrtoma Zone and Cyprideis paralela Zone), compatible with the Grimsdalea palynozone, from the middle to upper Miocene. A new Ostracod Association Zone named Cyprideis cyrtoma Association Zone is here proposed, which has an inferred age in the Tortonian and records the peaks of abundance and diversity of species, especially of the genus Cyprideis, throughout the cores studied herein and in those from previous studies. The great predominance of species of the Cyprideis genus in the studied material, in addition to the associated occurrence of rare freshwater and marine genera, points to a lacustrine, semi-confined, brackish and mesohaline environment.