Navegando por Assunto "Rio Paracauari - PA"

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Estudo sedimentológico dos paleocanais da região do rio Paracauari, Ilha de Marajó - estado do Pará
(Universidade Federal do Pará, 1981-11-19) BEMERGUY, Ruth Léa; TRUCKENBRODT, Werner Hermann Walter; http://lattes.cnpq.br/5463384509941553
This investigations deals with the paleochannels of the Paracauari river In the northeastern region of Marajó island, based on the photogeological interpretation of maps (scale: 1:20.000) and Sedimentological studies of 13 holes with maximun depth of 50 meters. Morphologically the paleochannels are caracterized by meandering forms and are easily recognized by the vegetation and topographic features. The paleochannels are constituted of texturally mature and well sorted sands. The study of the heavy minerals fractions shows that following species are more importante: tourmaline, staurolite, zircon, andalusite and kianite. These minerals constitute a mature suite whi.ch are not only from the Amazon river system but also from the Tocantins river system. The clay fraction are represented by kaolinite, montmorilionite, illite and chlorite. These mineralogical composition reveals the influente of the more them one climatic change. The possible sources areas for these minerals are: the Andes Mountains; the upper Amazon and the Tocantins basin from this work we conclude that the methods of sedimentological research presented here with the studies of the morphological patterns in the northern and northeastern regions of Marajó Island can be applied to groundwater prospecting.
Acesso aberto (Open Access)
Geofísica aplicada à prospecção de água subterrânea na área do Rio Paracauari – Ilha de Marajó - Pará
(Universidade Federal do Pará, 1979-08-24) CAVALCANTI, Gerardo Majela Lima; SAUCK, William August; http://lattes.cnpq.br/6655455534234531
The Rio Paracauari pilot study area in the east-central part of Marajo Island is typical of the low, planar, natural grasslands of this deltaic region. The cattle ranches of this area suffer considerable losses during the dry seasons because the groundwater is generally brackish. A 250 Km2 study area was chosen in wich geo-electrical methods were used to search for and outline any shallow fresh-water aquifers which might be present. Fifty-three Schlumberger vertical electric sondings were made on a grid of approximately 2 by 2.5 Km, as well as 5 horizontal Wenner resistivity profiles. The VES data were initially treated with the auxiliary point method and later, groups of models were constructed using a curve-generating routine to fit the field VES curves. The geo-electric results show two types of terrain. The first with higher resistivities, reaching to 950 ohm-m, is characterized by long (10 Km) belts up to one Km wide with dominantly sand sediments beginning near surface and extending to depths on the order of 60 m. These are saturated with potable water, with the water table typically at depths of only 2 to 5 m. These aquifer zones cover less than 30% of the area. The second type of terrain occupying the rest of the area has resistivities less than 6 ohm-m and often as low as 0.5 ohm-m, and is interpreted as silts and clays with saline water. Water samples taken from the surface and from shallow wells show a range of resistivities between 1.1 and 362 ohm-m. Seven drill holes were made, to depths as great as 54m. These verified the geophysical interpretations and clearly showed the differences between the channel-fill deposits which constitute the aquifers (channel sands or point bar deposits) and the fine, organic and clay-rich sediments of the adjacent flood-plain environment. Several of the drill holes were completed as water wells and now supply potable water on two of the ranches. Although the ages of the sediments are unknown, these large channels could have been excavated during the Pleistocene sea-level minimum and later filled with coarse, medium, and fine sand as sea level rose again, diminishing the velocities of the rivers or distributaries passing through the region. There has since been a drainage reversal, with the belts underlain by channel sands now existing as slight topographic highs, which could be explained by differential compaction.