Caracterização geológica-geofísica em uma área da Falha Açotéia-Piquiri aplicada a hidrogeologia, Santana da Boa Vista, RS

Abstract

The study on hydrogeology area aims to find structures and occurrence of groundwater in the northwest boundary of the Arroio Moirão Graben, located in the Sul-rio-grandense Shield, more precisely, on the Açotéia-Piquiri Fault (NE-SW direction). The research area is located southeast of Santana da Boa Vista, RS, near the Camaquã river, about 60 km from Caçapava do Sul, RS. In the municipal area there are several rock types, dating from the Paleoproterozoic to the Mesozoic, the main geological units currently in the field are: Ortognáissica Unit Complex Metamorphic Porongos (NW) and sedimentary rocks of the Sanga do Cabral Formation (SE), which are classified as aquitardo. Therefore, fractures and faults have an important role in hydrogeological standpoint. To identify them geophysical methods were used Remote Sensing, Electromagnetic Geoconductivity and Electrical Resistivity. Through orbital images of satellite Landsat 7 ETM + and its processing in SPRING 4.2, it was possible to identify lineaments and get the rosette diagrams with the absolute frequency. After this step were defined the electromagnetic traversal profiles in the direction NW-SE, orthogonal the Açotéia-Piquiri Fault. Two very weathered sandstone outcrops were observed in the region of the Paraná Basin and are few pebbles fragments in the area. The sediments in streams were analyzed for its composition, indicating that in the area there are large deposits of sediment ranging from clay to pebble, autoctones and alioctones materials. The geoelectric sections of apparent conductivity and resistivity exhibit similar behavior, clearly showing two distinct geological units and separated by a fault The Geoconductivity method provides better results for the identification of Açotéia-Piquiri Fault. Your geoelectric sections of apparent conductivity show low values (0-15 mS / m) to the basememt NW and high values (45-65 mS / m) for the Paraná Basin SE. The region associated with the fault presents intermediate values (16-44 mS / m) apparent conductivity, indicating completion of saturated detrital material So a more likely location for lease of a production well water is located at a point where failure at a depth of about 120 m, for greater lithostatic and hydrostatic pressure and consequently higher throughput.