The metropolitan area of Belém (RMB) is located in a distensive segment filled by sedimentary sequences of Pirabas and Barreiras Formations (COSTA et al., 1996) which constitute one of greater ground water reservoir of Brazil (Oliveira, 2003).
The aim of this work is to offer information about these aquifers units thorough using data from geology, geometry and cinematic, hydrogeology and morph tectonic, to comprehend the evolution of these units in space and time. Databank used in this work was obtained from: (1) field data; (2) information of well drilling; (3) topographic maps in scal1 1:100,000; (4) Landsat 7 images; (5) SRTM – Shuttle Radar Topographic Mission; and (6) GIS – Geographic Information System of RMB, Guajará and Marajó Bay. Softwares SPRING, Arc View and Global Mapper were used to process and treatment of data and images. Two main scales were used in this study: (1) a regional scale 1:100,000 evolving maps of Belém, Acará and Abaetetuba giving a total of 10,635 km2; and (2) a semi detail scale 1:25,000 adjusted at RMB with total of 1, 929 km2. Morph tectonic analysis showed three geomorphologic domains: Fluvial Plain Terrain, Terrain of Hills and Terrain of Small Mountains. The directions of topographic elements of terrain are compatible with the directions of the drainage net. The analysis of drainage net gave five main basin domains: (1) Coastal; (2) Marapanim River; (3) Guamá River; (4) Acará-Moju River; and (5) Pará River. Thorough this analysis was identified and defined neotectonic elements represented for lineaments from each hydrographic basin, with general directions NE-SW, NW-SE and NNE-SSW in regional scale. The RMB shows main directions in NE-SW and NW-SE with secondary trends WNW-ESE. Using projection and extension of lineaments presents in RMB, was possible to draw a two-dimensional model, which form three-dimensional blocks. Were defined two kinds of sectors based on distinct aspects of blocks. Sector I is located in southeast and Sector II is in northeast portion of RMB. There are kinematics variations in these two sectors. Sector I has dextral moving with stretching direction NW-SE and normal faults NE-SW. In the Sector II the cinematic is sinistral with stretching direction NW-SE and normal faults NE-SW associated. 4 Correlation between water wells located in different blocks proved that geologic layers present in both blocks have distinct attitudes, probably influenced by neotectonic processes. In Sector I, the gradient is moderate 1/180 m/m in the other hand Sector II has gradient 5x bigger 1/30 m/m. The different values on gradient suggest that Sector I and II are distinct with regarding to the slope of layers. With treatment integrated of information obtained was possible to establish the stretching direction for Pirabas-Barreiras Basin in NW-SE. Normal faults related to the development of basin have trends NE-SW. These structures are potential surfaces of low pressure, being favorable places to recharging of aquifers intercepted by its. So it is necessary to be worried about the possibility of pollution in these aquifers by human activity in these places of recharge. Since the recharge areas are exposed to urban or agricultural purposes.
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