Groundwater geochemical evolution in the northern portion of the Guarani Aquifer System (Brazil) and its relationship to diagenetic features

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The groundwater flow pattern in the northern portion of GAS (Guarani Aquifer System) is characterized by the existence of four regional recharge areas located in São Paulo, Mato Grosso do Sul and GoiAs states. From these areas of recharge the regional flow is radial and directed toward the center of the Parana Sedimentary Basin. Local discharge occurs in portions of outcrop regions. The groundwater has low mineralization and can be classified as Ca or Ca-Mg-HCO(3) type, Na-HCO(3) type and Na-HCO(3)/Cl/SO(4) type, this sequence represents the hydrochemical evolution. The mechanisms responsible for this evolution are dissolution of feldspars and removal of the carbonate cement from the sandstone mineral framework, followed by ion exchange, responsible for the increase in the Na concentration and decrease of Ca, and, finally, enrichment in Cl and SO(4) derived from underlying aquifer units. The hydrochemical evolution is consistent with diagenetic features that are observed in the sandstones, with the presence of siliceous cement in the outcrop areas, and carbonate cement toward the center of Parana Basin. (C) 2009 Elsevier Ltd. All rights reserved.