Fatores hidrogeológicos, espeleológicos e estruturais no desenvolvimento de zonas preferenciais de carstificação, nordeste do município de Sete Lagoas, MG

Abstract

The development of karst terrains is influenced by the interaction of various factors, ranging from regional to local scale. At the regional scale, tectonic processes can lead to the formation of geological structures such as shear zones, horsts, and grabens. At a more local scale, these structures transform into discontinuity zones in soluble rocks, such as limestones, where the percolation of meteoric water can preferentially enlarge fractures, faults, bedding planes, or folds, resulting in the formation of karst networks. This study investigated the main factors that enabled the development of preferential karstification zones and presented a 3D geological model of the area northeast of the municipality of Sete Lagoas, which has experienced significant urban and industrial growth in recent decades. To achieve these objectives, regional analysis methods were employed, including hypsometry and morphostructural lineaments, as well as regional geophysical techniques such as gravimetry, magnetometry, and radiometry. Local methods included geological, speleological, and structural mapping, along with the collection of groundwater level data from tubular wells, karst springs, and lakes, as well as geophysical surveys in areas of interest using electrical resistivity imaging (ERI). Regional results indicate that the preferential karstification zones follow NE-SW and NW-SE directions, linked to tectonic forces that form grabens and horsts in the basement, as well as weakness zones in the limestone and metapelite rocks of the Sete Lagoas and Serra de Santa Helena formations. The potentiometric surfaces show a regional flow direction towards the NE, with evident drawdown cones in at least three regions, particularly in the industrialized portion north of Sete Lagoas. Since the onset of industrialization in the 1980s, there has been a reduction of about 30 m in the water level, reaching up to 100 m in the industrialized area. Locally, geophysical sections from electrical resistivity indicated both lateral and vertical continuities of regional karstification zones, correlated with surface karst features such as cave entrances, sinkholes, lakes, and springs. The analysis of the data, compiled into a 3D geological model, contributes to the hydrogeological understanding of the northeastern part of the city of Sete Lagoas and serves as a basis for future studies in water resource management.