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Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Journal of South American Earth Sciences 31 (2011) 444e456 Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames Relation between sedimentary framework and hydrogeology in the Guarani Aquifer System in São Paulo state, Brazil Ricardo Hirata a,*, Ana Gesicki b, Ondra Sracek c,d, Reginaldo Bertolo a, Paulo César Giannini e, Ramón Aravena f a Laboratory of Physical Models e LAMO/CEPAS, Institute of Geosciences, University of São Paulo, Rua do Lago 562, 05508-080 São Paulo (SP), Brazil b National Department of Mineral Production (DNPM), São Paulo District, Rua Loefgreen, 2225, 04040-000 São Paulo (SP), Brazil c Dep. of Geology, Faculty of Science, Palacký University, 17. listopadu 12, 771 46, Olomouc, Czech Republic d OPV s.r.o. (Protection of Groundwater Ltd), Belohorská 31, 169 00 Praha 6, Czech Republic e Institute of Geosciences, University of São Paulo, Rua do Lago 562, 05508-080 São Paulo (SP), Brazil f Department of Earth and Environmental Sciences, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1 article info abstract Article history: This paper presents the results of a new investigation of the Guarani Aquifer System (SAG) in São Paulo Received 19 July 2010 state. New data were acquired about sedimentary framework, flow pattern, and hydrogeochemistry. The Accepted 11 March 2011 flow direction in the north of the state is towards the southwest and not towards the west as expected previously. This is linked to the absence of SAG outcrop in the northeast of São Paulo state. Both the Keywords: underlying Pirambóia Formation and the overlying Botucatu Formation possess high porosity (18.9% and Guarani Aquifer System 19.5%, respectively), which was not modified significantly by diagenetic changes. Investigation of sedi- Transboundary aquifer ments confirmed a zone of chalcedony cement close to the SAG outcrop and a zone of calcite cement in the Sedimentary framework fi Flow pattern deep con ned zone. The main events in the SAG post-sedimentary history were: (1) adhesion of ferru- fi Cation exchange gineous coatings on grains, (2) in ltration of clays in eodiagenetic stage, (3) regeneration of coatings with Environmental isotopes formation of smectites, (4) authigenic overgrowth of quartz and K-feldspar in advanced eodiagenetic stage, (5) bitumen cementation of Pirambóia Formation in mesodiagenetic stage, (6) cementation by calcite in mesodiagenetic and telodiagenetic stages in Pirambóia Formation, (7) formation of secondary porosity by dissolution of unstable minerals after appearance of hydraulic gradient and penetration of the meteoric water caused by the uplift of the Serra do Mar coastal range in the Late Cretaceous, (8) authigenesis of kaolinite and amorphous silica in unconfined zone of the SAG and cation exchange coupled with the dissolution of calcite at the transition between unconfined and confined zone, and (9) authigenesis of analcime in the confined SAG zone. The last two processes are still under operation. The deep zone of the 13 SAG comprises an alkaline pH, NaeHCO3 groundwater type with old water and enriched d C values (<À3.9), which evolved from a neutral pH, CaeHCO3 groundwater type with young water and depleted d13C values (>À18.8) close to the SAG outcrop. This is consistent with a conceptual geochemical model of the SAG, suggesting dissolution of calcite driven by cation exchange, which occurs at a relatively narrow front recently moving downgradient at much slower rate compared to groundwater flow. More depleted values of d18O in the deep confined zone close to the Paraná River compared to values of relative recent recharged water indicate recharge occur during a period of cold climate. The SAG is a “storage-dominated” type of aquifer which has to be managed properly to avoid its overexploitation. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction There are several large aquifer systems around the world. One of the most important is the Guarani Aquifer System (SAG, from the Spanish and Portuguese abbreviation), located in the Paraná sedi- mentary basin in South America (Fig. 1) with a surface area of * þ þ Corresponding author. Tel.: 55 11 30914804; fax: 55 11 30914207. 1.1 million km2. This is an intracratonic basin comprising sedi- E-mail addresses: [email protected] (R. Hirata), [email protected] (A. Gesicki), [email protected] (O. Sracek), [email protected] (R. Bertolo), [email protected] mentary sequences from the Silurian-Devonian up to the Creta- (P.C. Giannini), [email protected] (R. Aravena). ceous. The main water-bearing rocks are Cretaceous eolian 0895-9811/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsames.2011.03.006 Author's personal copy R. Hirata et al. / Journal of South American Earth Sciences 31 (2011) 444e456 445 Fig. 1. Potentiometric surface of SAG in São Paulo state and surroundings and location of sampled wells (associated to the cities) (modified and adapted from LEBAC, 2008 and Silva, 1983; and other sources: DAEE, IG, IPT, CPRM, 2005; PSAG, 2009; Assine et al., 2004). sandstones of the Botucatu Formation, which in São Paulo state are personal collections. The samples were prepared with blue epoxy underlined by Triassic fluvial-eolian argillaceous sandstones of the resin-impregnation and examined under petrographic microscope. Pirambóia Formation, and both formations are overlain by volcanic Representative samples were examined under an SEM (Scanning rocks, mainly basalts, of the Serra Geral Formation. Electron Microscope) equipped with EDS (Energy Dispersion The transboundary SAG extends to several countries, including Spectrometer) at the Institute of Geosciences, USP, for identification Brazil, Paraguay, Uruguay, and Argentina (Araújo et al., 1999). The of micromorphology and diagenetic components relationships. principal development of the SAG for drinking and industry uses is Groundwater samples were collected directly from the 25 in São Paulo state, representing more than 70% of SAG total operating water wells in the states of São Paulo, Mato Grosso do Sul, exploited yield (Foster et al., 2009). and Goiás (Fig. 1 and Table 1). The parameters determined in the The evolution of water chemistry and isotopic composition of field were temperature, pH, Eh, dissolved oxygen, and electric the SAG groundwater in São Paulo state has been studied by several conductivity, using glass electrodes. The alkalinity was also inves- investigators, including Gallo and Sinelli (1980), Silva (1983), tigated in the field and analyzed by titration with H2SO4, using the Kimmelmann et al. (1989a), Araújo et al. (1999), Meng and end-point based on the Gran plot (Appelo and Postma, 1993). Maynard (2001), Sracek and Hirata (2002), and Gastmans et al. Samples for cation analysis were filtered in the field by 0.45 mm (2010). The two last articles discussed a conceptual model based cellulose acetate membrane and acidified with ultrapure nitric acid on progressive downgradient movement of a cation exchange front to pH < 2. Analyses for cations (Ca, Mg, Na, K, Mn, Fetotal, Al, Ba, Pb, coupled with dissolution of carbonates, with resulting evolution of Zn, Cu, Ni, Cr, Cd, Sr, Ag, and dissolved silica) were performed by groundwater from CaeHCO3 type and lightly acid in the unconfined inductively coupled plasma-optical emission spectrometry zone towards NaeHCO3 type with high pH in the deep confined (ICP-OES - SMEWW 3120B method) at the laboratory of the zone. The objective of this study is to refine previous conceptual models of flow pattern and hydrogeochemical evolution in the SAG Table 1 List of sampled wells. in São Paulo state, based on new sedimentological and hydro- geochemical data. Then, these data are compared and discussed Code Town Code Town within the framework of flow pattern, groundwater chemistry, and MAT Matão ADD Andradina isotopic chemistry. JAB Jaboticabal ARÇ Araçatuba SER Sertãozinho EPI Presidente Epitácio BAT Batatais PRU Presidente Prudente 2. Material and methods SJB São Joaquim da Barra PGU Paraguaçu Paulista GUA Guaíra MRL Marília Diagenetic studies of the Pirambóia and Botucatu formations BAR Barretos TUP Tupã were performed by petrographic analysis of 130 cutting samples OLI Olímpia LIN Lins SRP São José do Rio Preto BAU 1 Bauru obtained during drilling of 30 water wells located in São Paulo FER 3 Fernandópolis BAU 2 Bauru State, as well as outcrop (11) and oil exploration well core samples FER 2 Fernandópolis AGU Agudos (9). Rock samples of well cuttings were obtained from DAEE CAS CassilândiaeMS SBB Águas de Santa Bárbara (Department of Water and Electric Energy) and CPRM (Brazilian LSA Lagoa Santa eGO TIM Timburi Geological Survey) and samples from oil exploration wells from MS: state of Mato Grosso do Sul; GO: state of Goiás otherwise, state of São Paulo. Author's personal copy 446 R. Hirata et al. / Journal of South American Earth Sciences 31 (2011) 444e456 Institute of Geosciences (IGc-USP). Anions (Cl, F, Br, NO3,PO4,SO4, cross bedding at a decimeter scale, deposited in amalgamated S) and DOC analyses were processed at Bioagri Ambiental labora- layers or intercalated with well sorted fine sandstones with cross tory (São Paulo, Brazil) by ionic chromatography (SMEWW 4110C stratification.