Análise geomorfológica da região entre os municípios de Itacoatiara, Silves e Iitapiranga, nordeste do Estado Amazonas

Abstract

The studied area is located in the northeast part of the State of Amazonas, along the State roads AM-010 and AM-363. It encompasses the cities of Itacoatiara, Silves and Itapiranga, which are inserted in the morphostructural units of the River Trombetas Desiccated Plateau Negro River and the Amazonian Plain. This research has as main objective to characterize the geomorphologic and morphostructural features and to correlate them with the geological units, by means of the cartographic bases in the 1:100,000 scale of the cities of Itacoatiara-Sheet SA.21-Y-D4/Ml-582; ltapiranga-Sheet SA.21-Y-B-IV/Ml - 0521; Anebá - Sheet SA.21-Y-Vl/Ml-520 and São José do Amatari-Sheet SA.21-Y-C-lll/Ml - 58, as well as with the interpretations of the remote sensor images (MDT)/SRTM (Shuttle RADAR Topography Mission), LANDSAT-5 of TM sensor and field work. The geomorphologic features are built up on rocks of the Alter do Chão Formation and of the Novo Remanso Formation; these features were carved under the influence of endogenetic factors (tectonic movements with faults) and exogenetic (climatic actions: weathered and erosive). The relief in the River Trombetas Desiccated Plateau - Negro River is desiccated, and shows plateau and hills shape. The hills present convex tops (Dc) with altimetry and amplitude up to 1 km of extension for 200m of width reaching 80m. On the other hand, the plateaus display smoothed and preserved tops (Dptac), convex tops (Dptc) and smoothed tops (Dpta), with amplitudes that range I to 8 km of extension, with 100 to 400m width and altimetry up to I 50m. In the restricted area of the Amazonian Plain, the more representative relief shapes are fluvial terraces, paranas (connecting rivers), islands, lakes and furos, that are mainly under the influence of the hydrodynamic actions of the Amazon River. The draining net is constituted by the Amazon River and its main tributaries: Uatumã, Anebá, Caru and Urubu rivers. The draining pattern that predominates is the dendrict, although in the southwestern part of the studied area predominates the subdendrict pattern, in the environs of the Canaçari Lake is the orthogonal pattern, in the Units Cl, F2, F3 and G, predominates the treliça, and to the south, the ring pattern. The area displays several representative structural segments of first order, that have preferential directions NW-SE and SW-NE which controls the direction of the Amazon, Uatumã, Anebá, Caru and Urubu rivers. In turn, the structural segments of second order, which have N-S and NNE-SSW direction, control the relief and the hydrography of the area, whose main consequence is the alignment of the valleys and ridges, and the directions of the rivers and igarapés from the first to the fourth orders. The geometric analysis of the photointerpreted structural elements combined with field work observations resulted in the identification of normal faults in listric arrangements and allowed to elaborate a morphostructural model represented by a system of scalonated prisms that deep about 25° to SW. From the pedologic point of view, sand deposits and Iatossoils with red-yellow colors are found, as well as ferruginous lateritic profiles with well defined horizons, with a mineralogical composition of quartz, kaolinite, hematite and goethite.