Navegando por Assunto "Amazon Basin"

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Amphibians and reptiles from Floresta Nacional de Pau-Rosa, Amazonas, Brazil: an important protected area at the heart of Amazonia
(Instituto Nacional de Pesquisas da Amazônia, 2017-09) FERREIRA, Gisele Cassundé; STURARO, Marcelo José; PELOSO, Pedro Luiz Vieira Del
Amazonia harbors the largest and most diverse tropical forest in the world, but knowledge about the species diversity of the region is still far from ideal. Given this low level of faunal and floral knowledge, we present an annotated list of the species of amphibians and reptiles found in Floresta Nacional do Pau-Rosa (FNPR), along the Rio Paraconi, municipality of Maués, state of Amazonas, Brazil. Herpetofauna of the FNPR was sampled with pitfall traps, active search and occasional encounters from February 18 to March 28, 2009. A total of 270 specimens were collected, representing 39 species of amphibians and 24 species of reptiles. At least seven of the species collected at FNPR represented, at the time, unnamed taxa (four of which have now been named). The number of taxa collected and the high number of unnamed taxa highlight the importance of this area in terms of biodiversity and as a priority for conservation. We also discuss about the amphibian diversity in Amazonia.
Acesso aberto (Open Access)
Modelagem sísmica via métodos das diferenças finitas: caso da bacia do Amazonas
(Instituto Nacional de Pesquisas da Amazônia, 2009-03) FERNANDES, Lindemberg Lima; CRUZ, João Carlos Ribeiro; BLANCO, Claudio José Cavalcante; BARP, Ana Rosa Baganha
This paper discusses the seismic modeling in medium with strong discontinuities in its physical properties. The approach takes in consideration the existences diffractions and multiple reflections in the analyzed medium, which, at that case, is the Amazon Basin. The stability and boundary conditions of modeling were analyzed by the method of the finite differences. Sedimentary rocks deposited since the Ordovician to the present, reaching depth up to 5 Km. The bodies of diabasic between the paleozoic sediments are layers reaching thickness of hundred meters, which add to 90.000 km3, form the geology of the Amazon Basin. The occurrence of these structures is responsible for multiple reflections during the propagation of the seismic waves, which become impossible a better imaging of horizons located bellow the layers. The representation this geological situation was performed an (synthetic) acoustic velocity model. The numerical discretization scheme is based in a fourth order approximation of the acoustic wave equation in space and time The understanding of the wave propagation heterogeneous medium has improved for the application of the finite difference method. The method achieves a good resolution in the interpretation of seismic reflection events. The numerical results discusses in this paper have allowed to observed the influence of the multiple reflection in a high velocity layer. It increase a loss of energy and difficult the interpretation of the target. For this reason the integration of surface data with the well data is recommended, with the objective to get one better image of the targets below of the diabasic layer.
Acesso aberto (Open Access)
Proveniência sedimentar dos depósitos cretáceos da Formação Alter do Chão, Bacia do Amazonas, região de Ponta do Curuá, Prainha-PA
(Universidade Federal do Pará, 2020-08-03) SANTOS, Raiza Renne Leitão dos; SOARES, Joelson Lima; http://lattes.cnpq.br/1345968080357131
Deposits of the Alter do Chão Formation are found along the right bank of the Amazon River and are well registered in the locality of Ponta do Curuá, municipality of Prainha, the western region of the State of Pará. The outcrops are characterized by thick layers of fine to coarse sandstones interbedded with siltstones and claystones, and subordinate subordinate conglomerates. The facies analysis carried out in these outcrops allowed the individualization of 8 sedimentary facies, grouped in three facies associations (AF), configuring a high sinuosity and mixed load fluvial meandering depositional system. AF1 comprises facies with a thicker granulometry of the studied succession and was interpreted as the filling of the fluvial channel, characterized by massive to stratified conglomerates, massive sandstones, sandstones with trough and tabular cross-bedding, sandstones with convoluted laminations and climbing crosslaminations. AF2 was interpreted as abandoned channel filling deposits and corresponds to thick layers of massive to laminated mudstones that are sporadically associated with thin layers and very thin sandstone lenses forming wavy-linsen bedding. Well-preserved leaves and trunks are present in this association. AF3 corresponds to the flood deposits, composed of massive to laminate mudstones, massive sandstones, and sandstones with trough, tabular and sigmoidal cross-stratifications. The study of heavy minerals in the sandstones of this formation showed an assembly with a predominance of ultra-stable minerals such as zircon, tourmaline, rutile and anatase, and less frequent minerals such as kyanite, staurolite, sillimanite, andalusite, and garnet. Metasedimentary sources are suggested due to the presence of aluminum-rich metamorphic minerals. Whereas, rutile and tourmaline are present in both igneous and metamorphic rocks, being more common in the latter. Well-rounded minerals suggest an origin from sedimentary deposits, in the same way that subhedral and euhedral minerals suggest first cycle sediments. The high stability of this assembly is attested by the high compositional maturity exhibited by these sandstones, with values of the ZTR index ranging from 69% to 99%. These high values indicate that chemically unstable minerals have been eliminated over geological time, probably due to the action of interstitial fluids that circulate in the porous during weathering and diagenetic processes. However, the analyzed mineral assembly is more compatible with conditions of exposure to intense chemical weathering. The effects of intrastate dissolution in the area is directly proportional to the increase in the ZTR index, being attested by the presence of corrosion textures on the surface of the minerals that were analyzed from SEM images. Thus, the mineralogical assembly would reflect the effects of the intense chemical weathering, under a humid tropical climate, imposed on the deposits of the Alter do Chão Formation that would be associated with the lateritization event responsible for the genesis of bauxite deposits during the Paleogene. Recently, the luminescence (LC) characteristics of quartz grains have been used as provenance indicators, mainly in rocks affected by weathering or rich in quartz. In this work, luminescence signals were acquired by polychromatic cathodoluminescence to establish the relationship between luminescent signals and the genesis of this mineral. The studied grains present red, blue, violet and brown colors, with different intensities: the reddish-brown tones, are generally attributed to metamorphic rocks; dark blue luminescence is a characteristic observed in quartz of plutonic origin; grains with intense LC such as blue, red and violet of high bright, are volcanic quartz. Geochronological analyzes carried out on detrital zircons using the U-Pb method allowed to determine that the main sources for the Alter do Chão Formation are Paleoproterozoic ages, subdivided into two groups: (1) 1771 to 1906 Ma; and (2) 1957 to 2037 Ma, in addition to a small Archean contribution (Neoand Meso-Archean) aged between 2529 and 2977 Ma. The data from the first group, 1771 and 1906 Ma, were correlated with the age of provenance of metasedimentary rocks from the Araguaia Belt, which occurs on the eastern edge of the Amazon Craton. Ages around 1957 and 2037 Ma are consistent with rocks from the Maroni-Itacaiúnas Province, located on the eastern edge of the basin. It is possible to mention rocks associated with late to post-collisional orogenic magmatism such as the Igarapé Careta Intrusive Suites (2065 ± 33 Ma), Parintins (2030 ± 3 Ma) and paleoproterozoic indistinguishable granitoids occurring in the Amapá Block and Carecuru Domain, in addition to rocks related to post-orogenic magmatism such as the Granodiorito Sant'Ana (1986 ± 5 Ma) of the Bacajá Domain. Archean contributions can be associated with rocks from the Central Amazon Province or even to Archean nuclei distributed in the region.