Conditioning local structures of the geometric and hydraulic characteristics of the Guarani Aquifer System (GAS): the Santa Helena farm structural high, boa Esperança do Sul, São Paulo, Brazil

Abstract

Fazenda Santa Helena High (FSHH) is the name given to the local structure identified by well drillings for groundwater extraction in the Guarani Aquifer System (GAS), housed in Jacaré-Guaçu High, into the region of the Jacaré-Guaçu and Jacaré-Pepira basins, Boa Esperança do Sul Municipality, São Paulo State, Brazil. This structure, whose limits have not yet been delimited, affects the geometric and hydraulic characteristics of the SAG. Data from deep wells and borehole logging showed that the SAG is represented in the area by fine to very fine clayey sandstones, with frequent Interbedded shale layers. This succession belongs to the basal portion of the Piramboia Formation and lies above unconformity on siltstones and shales of the Corumbataí Formation. The reduced thickness of about 80 m and the lithologic characteristics of the SAG affect negatively the aquifer transmissivity, resulting in low-productivity wells. The present article reveals the existence of this substructure that exerts influence on the water storage and the local potentialities of the SAG, and draws attention to the possibility that there are innumerable others in a similar geological context or hidden under the coverage of the basaltics of Serra Geral Formation and sedimentary rocks of Bauru Group.