The central region of the Amazon is located within the largest drainage basin in the world. In the basins of the Uatumã and Urubu rivers in this region, the landscape have drainages with long straight stretches, abrupt inflections, course changes evidenced by abandoned meanders, and basin asymmetries, and smooth variations of the landscape dissection and roughness patterns, which are morphological features suggestive of the action of modern tectonic activity. Geologically, the study area is covered by Tertiary sediments that are cut by normal faults and joints. To identify the influence of surface and subsurface geological structures on relief, we applied geomorphometric techniques on the digital elevation model from SRTM. These techniques have been separated into two groups: 1) basin asymmetry, isobase and river sinuosity were used for reveal the genesis of relief forms, and 2) fractal geometry, drainage density and semivariogram were used to verify the spatial distribution of the roughness, dissection and elevation. Furthermore, the trend-surfaces were also observed by elevation (semivariograma), roughness (self-affine fractal geometry) and drainage density anisotropy (self-similarity fractal geometry). The results of the first group permited the delineation of nine geomorphological domains that exhibit preferential migration paths and a potential relationship to block tilting. The comparison of the boundaries of these domains with geological and geophysical data suggests that these boundaries are likely related to subsurface faults that would have controlled the generation of younger faults and the relief modelling of the region. This interpretation is confirmed by the correspondence between subsurface and surface faults and the boundaries and shapes of the domains, the change in the sinuosity of rivers when crossing boundaries, and the effects of a high concentration of seismic activity along one of the limits on the region. Other geomorphological data also indicate structural control of the relief. There is a relationship between the orientation and approximation of the isobase map lines and the high-angle normal faults mapped in the floodplains of the main rivers. For the second group of variables, the results reveal the spatial coincidence between domains, defined by the analysis of roughness (fractal dimension) and elevation (semivariogram), and subsurface geological structures. This is the case in the area of Silves, where the undulating relief exhibits drainage with annular and radial patterns, coinciding with faults and folds previously mapped by seismic surveys. Another example of such influence is the combination of high magnetic with low dissection pattern mapped by drainage density. In addition to the spatial distribution, trends of these geomorphometric variables were compared among themselves and also with geological information. The results indicate that the predominant directions of the major anisotropy axis is NNE-SSW and NE-SW for the interfluve regions, and NW-SE to the alluvial plains. The ...
ABSTRACT. The availability of digital elevation models produced by the SRTM (Shuttle Radar Topographic Mission) opened new possibilities for studies of geological remote sensing in the Amazônia, since these models enhance subtle details of the terrain and drainage system, usually masked in conventional orbital images. Using as a case study an area located in the Amazonas sedimentary basin, this article discusses an approach to use these data as an aid to oil exploration in that region. The analysis of the drainage network automatically extracted from that product, combined with altitude information provided by the digital elevation model, revealed a number of drainage anomalies, which may indicate surface expression of buried geological features. One of these drainage anomalies is located exactly within the limits of the Azulão Gas Field, and may correspond to the surface expression of the hydrocarbon trapping structures in that area. The methodological approach discussed in this study can be replicated elsewhere in the Amazonas and Solimões sedimentary basins, which together comprise about 1,000,000 km 2 covered by rainforest.Keywords: SRTM elevation data, morphostructural analysis, petroleum exploration, Amazonas Basin. RESUMO.A disponibilidade de modelos digitais de elevação gerados com pela SRTM abriu novas possibilidades para estudos de sensoriamento remoto geológico na região amazônica, uma vez que tais modelos realçam detalhes sutis da morfologia do terreno e da rede hidrográfica, geralmente mascarados em imagens orbitais convencionais. Usando como estudo de caso umaárea localizada na Bacia do Amazonas, o presente artigo discute uma abordagem para uso desses dados como subsídiò a exploração petrolífera na região. A análise da rede de drenagem extraída automaticamente daquele produto, aliadaà informação altimétrica, revelou várias anomalias de drenagem que podem indicar expressão em superfície de feições geológicas em profundidade. O campo de gás de Azulão está situado exatamente nos limites de uma dessas anomalias de drenagem, sugerindo que ela deva representar a expressão morfológica das estruturas responsáveis pelo trapeamento dos hidrocarbonetos naquelá area. A abordagem metodológica discutida neste artigo poderá ser replicada em outras bacias sedimentares, especialmente nas Bacias do Amazonas e do Solimões, com cerca de 1.000.000 km 2 cobertos pela floresta tropical.
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