Navegando por Assunto "Amazon River"

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Acesso aberto (Open Access)
Hidrodinâmica, transporte e proveniência sedimentar no baixo rio xingu e sua importância como “Tidal River” amazônico
(Universidade Federal do Pará, 2022-07-14) MEDEIROS FILHO, Lucio Cardoso de; LAFON, Jean Michel; http://lattes.cnpq.br/4507815620234645; ASP NETO, Nils Edvin; http://lattes.cnpq.br/7113886150130994
This research is based on the investigation of the processes (geological and hydrodynamic) that govern the recent evolution of a large tributary of the lower Amazon, the Xingu River. The aim was to investigate its aspects of sedimentary evolution and hydrological flows, from already consolidated data on the filling of its ria and how its patterns of transport and sediment trapping, its seasonal and tidal effects have been established, in addition to understanding the role of the Amazon River as a regulator in the dynamics of its tributary. Hydrodynamic measurements of flow, velocity and water level along with bottom sediment and MPS samples were collected at 3 annual seasons (February, June and November). The results provided support for the investigation of the Xingu-Amazonas interaction and the evolution of the bottom morphology of the lower Xingu. The results suggest a filling of the ria both by the Xingu River, forming a prominent headwater delta, and the Amazon River, where tidal variations transport sediments upstream in the Xingu River. On the other hand, large areas in the central part of the ria indicate muddy sedimentation. Elementar geochemistry allowed us to trace part of the history of sediments and source rocks, together with the analysis of immobile elements (Al, Ti, Zr, Hf, Th) and rare earth elements (REE) because they are poorly fractionated during weathering processes. and they are concentrated in the bottom sediments to the detriment of the dissolved fraction of the rivers. The deposits preserved in the lower Xingu River, despite draining cratonic regions in higher areas, confirm that the bottom material is derived from heterogeneous sources with predominantly intermediate igneous compositions and that they underwent important recycling during fluvial transport. The hydrodynamic modeling allowed to indicate the fluvial discharge as the most relevant forcing for the muddy deposition dynamics in the Xingu estuary. From a numerical model, it was possible to extrapolate the flow and transport dynamics beyond the open boundaries, that is, the central portion of the ria, elucidating the interaction mechanism between river and tidal discharge and the associated sedimentary dynamics. The determination of the amplitudes and phases of the tidal components, whether of purely astronomical origin or resulting from shallow waters, as well as the average level and the hourly discharge proved to be fundamental for the understanding of the governing processes.
Acesso aberto (Open Access)
Modelo de propagação usando dois raios com modificação de fase para mobilidade aplicado a receptor LoRa sobre rio.
(Universidade Federal do Pará, 2024-09-19) RIBEIRO, Lucian Morais; BARROS, Fabrício José Brito; http://lattes.cnpq.br/9758585938727609
As predicted by experts, there has been exponential growth in the number of IoT devices used by the general population. Among these devices, one of the most notable groups is the Long Range (LoRa) devices. The most relevant feature of LoRa technology is its low energy consumption, while simultaneously providing a wide coverage area. If applied in the Amazon region – a densely forested, humid area with populations far from urban centers and with very little infrastructure – this technology could offer a new range of services to the region’s inhabitants, including services involving communication on the move. Starting from the principle that the most well-known propagation models are not adjusted to the specificities of the Amazon region, nor do they consider the phase variations caused by receiver movement – which makes radio links difficult to predict – we aim to present solutions to this problem through this work, which presents adjustments to the Two-Ray propagation loss model to accommodate LoRa communications over the Amazon rivers when the receiving devices are in motion. The proposed model is compared to the standard Two-Ray Model, which serves as the baseline, and achieves better results. Additionally, the study evaluates the impact of tides on the propagation loss of LoRa signals in river environments.
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.