Abstract
The Guarani (GAS) and Serra Geral (SGAS) aquifer systems are the main groundwater sources in southern Brazil. We investigated the crucial relationship between the primary, intergranular pore system in the GAS and the secondary pore system associated with fractures in the SGAS in order to understand better the compartmentalization and connection, water storage, and productivity of both aquifers. Data from 375 wells that produce from both aquifers was used to evaluate the hydrodynamic characteristics of the GAS-SGAS contact. The integration of data using remote sensing, structural data, and thin section analysis support interpretations about the compartmentalization and potential connection of the aquifers. Fault zones trending NW, EW, and NNE demarcate six structural blocks in which the GAS-SGAS contact varies more than 400 m in elevation. Thin section analysis of sandstone texture and composition allowed us to determine the relationship between the type of porosity and cement type and content. The surface demarcating the Guarani-Serra Geral contact is highly productive in 93% of the wells that reach both aquifers. The integration of our results allowed us to propose a conceptual hydrogeological model for the GAS and SGAS aquifers in the study area.
Highlights
Granular and fractured aquifer systems constitute most of the groundwater sources available for human, industrial, and agricultural activities throughout the world
The 35 lineaments identified on a 1:750,000 scale included a set of 8 lineaments of more than 15 km in length, which were recognized as geomorphological features, and coincident with the valleys of the most important rivers (e.g., Sinos, Paranhana, Rolante, Ilha, and Areia rivers – see Fig. 1) that limit six structural blocks in the study area (Fig. 2)
The recharge zone is in the North of the study area, while the discharge zone is along the Sinos River, running parallel to the main tectonic lineament
Summary
Granular and fractured aquifer systems constitute most of the groundwater sources available for human, industrial, and agricultural activities throughout the world. This context is crucial for hydrogeological research, as the Continental Flood Basaltic provinces (CFB) represent the most extensive magmatic flows recorded in geological history ( Jerram and Widdowson 2005, Waichel et al 2012) They are recorded in the Deccan Plateau in India (Kulkarni et al 2000, Katpatal et al 2014), Paraná-Etendeka in South America and South Africa (Erlank et al 1984, Peate et al 1990), Rio Columbia Plateau in the USA (Whiteman et al 1994), Golan Heights in Israel (Dafny et al 2006), and Dalha Basalts in Djibouti, Africa ( Jalludin and Razack 1994). Large aeolian deposits are older than basalts, but they can be coeval with those rocks bearing fractures, locally juxtaposing the basalts (Almeida and Melo 1981, Scherer 2000, 2002)
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