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Journal of South American Earth Sciences 31 (2011) 444e456

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Journal of South American Earth Sciences

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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 (<3.9), which evolved from a neutral pH, CaeHCO3 groundwater type with young water and depleted d13C values (>18.8) 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 sedimentary 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

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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 hydrogeochemical 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

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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. These coarse facies are associated with the advance of method) and high-temperature combustion (HTC e SMEWW a braided fluvial system, informally named Itirapina Sandstones by 5310B method), respectively. Caetano-Chang and Wu (2006) and Caetano-Chang (1997). A Per- The QA/QC procedures of the water analyses included analyses mianeTriassic age has been proposed for this formation on the of blanks, spikes, and laboratory duplicates, and the results indi- basis of its lower abrupt, non-erosional, and interbedded contact cated that the analyses presented satisfactory accuracy and preci- with the Corumbataí and Teresina formations (Passa Dois Group), sion. The global analytical error of the analyses was evaluated deposited in an epicontinental marine context during the Late through ion balance, and the results are within the acceptable Permian (Lavina, 1991; Giannini et al., 2004). range of 5%. Considering a wet eolian depositional system for Pirambóia Samples for d2H and d18O analysis were bottled directly in the Formation, revealed by the presence of mudstones and siltites of field and determined by mass spectrometry at the laboratory of the interdunes deposits, the water table probably was near to the Geochronology Research Center (CPGeo, IGc-USP, Brazil), but only depositional surface (Giannini et al., 2004). Considering the lateral d18O were used for interpretation because spatial trends for both coexistence of the eolian system (Pirambóia) and the shallow marine isotopes were similar. Determination of d13C was performed at Beta system (Passa Dois), the first system can be characterized by coastal Analytic, Florida (USA) by standard AMS. dunefield (Giannini et al., 2004), with its phreatic level directly Multivariate statistical analyses were performed, using the controlled by the “Passa Dois” relative sea level fluctuations. To the program PAST (Hammer et al., 2001) and speciation modeling was top of the Pirambóia Formation is a decreasing frequency of fine- performed by the program PHREEQC (Parkhurst and Appelo, 1999). grained strata as a consequence of less influence of water in interdunes, probably related to regressive conditions of the “Passa Dois” 3. Sedimentary framework of the Guarani Aquifer System coast line. The existence of a fluvial depositional system at the top of this formation (Itirapina Sandstones) reveals conditions of tectonic 3.1. Geological context activity in the basin (Caetano-Chang and Wu, 2006). The Botucatu Formation is composed of commonly reddish, very The Paraná and Chacoparaná basins are a large intracratonic fine to medium-grained sandstones arranged in sets of cross strat- depression of Paleozoic and Mesozoic age, which covers an ification of medium- and large-scale (5 m thick and hundreds of extensive area (around 1.4 million km2) in part of Brazil, Argentina, meters long in average), attributed to giant crescent eolian dunes. Paraguay, and Uruguay. Its thickness of 7000 m comprises sedi- This formation has characteristic monotonous facies, which are mentary and igneous rocks accumulated in tectonic-sedimentary related to the conditions of interior desert or erg (among others, transgressiveeregressive cycles separated by basin-wide uncon- pioneering studies by Washburne, 1930; Almeida, 1953, 1954 in formities, arranged in four major depositional sequences (Milani Gesicki, 2007) and more recently interpreted as a dry eolian depo- et al., 1994, 1998; Santa Ana et al., 2009). sitional system (Scherer, 2000) due to the absence of humid inter- The deposition of Pirambóia and Botucatu formations repre- dunes. The Botucatu formation age is assumed by some authors (e.g. sents late stages of tectonic-sedimentary evolution of the Paraná Milani et al., 1998) to be from the terminal Jurassic to the initial basin, which mark conditions of progressive continentalization of Cretaceous as interpreted on the basis of the lavas of Serra Geral Western Gondwana from the Late Permian to the Early Cretaceous. Formation (137e127 Ma, Turner et al., 1994), which covered dunes The final stage of the basin evolution is represented by Early rapidly and preserved them from erosion (Scherer, 2002). Cretaceous volcanism (Serra Geral Formation), and is responsible for the accumulation of up to 2000 m of tholeiitic basalts and 3.3. Pirambóia and Botucatu formations: texture, mineralogy, and dacites with interbedded eolian sandstones (Salamuni and diagenesis Bigarella, 1967; Soares, 1973, 1975). The Pirambóia and Botucatu formations are composed mainly of In terms of grain size, there is a clear trend of coarsening upward sandstones. They were deposited in distinct eolian sedimentary in the Pirambóia Formation and the opposite trend is observed in conditions and are separated by an unconformity of uncertain age the Botucatu Formation (Donatti, 2002). hiatus (Donatti et al., 2001). Both formations are frequently studied The Pirambóia Formation is characterized by fine to medium- together because it is difficult to distinguish between them, espe- grained sandstones deposited in dunes (grain sizes from 176 to cially in a hydrogeological context. However, they are different from 200 mm), fine to very fine-grained sandstones deposited in inter- genetic, depositional, age, and diagenetic evolution viewpoints. dune plains (grain size about 140 mm), and coarse-grained to conglomeratic sandstones at the top (grain sizes from 100 to 3.2. Stratigraphy and genetic model 110 0 mm, average 390 mm) (Caetano-Chang and Wu, 2006; Gesicki, 2007). On the other hand, the Botucatu Formation is characterized Recently, the deposition of Pirambóia Formation has been by fine to medium-grained sandstones (from 195 to 210 mm). attributed to the context of a wet eolian system (Donatti et al., Sorting in eolian sandstones, using Folk and Ward’s nominal clas- 2001; Giannini et al., 2004; Assine et al., 2004) and the Botucatu sification (Folk, 1968), varies from moderate to good (average Formation to a dry eolian system (Scherer, 2000; Donatti et al., standard deviation s ¼ 0.57) and from poor to very good 2001; Assine et al., 2004; Giannini et al., 2008), sensu termi- (s ¼ 0.3e1.3) in fluvial-eolian sandstones (Gesicki, 2007). nology defined by Kocurek and Havholm (1993). The sandstones of the Botucatu Formation and the upper part of The Pirambóia Formation (Late PermianeEarly Triassic) is the Pirambóia Formation (Itarapina Sandstones) are essentially characterized by very fine to medium-grained sandstones with composed of quartz arenites, with minor proportion of subarkoses medium-scale trough cross stratification (sets of 1e3 m thick), (sensu Folk, 1968). In contrast, the eolian sandstones of the attributed to eolian dunefields, besides intercalations of very fine Pirambóia Formation are predominately composed of feldspathic siltic sandstones, siltites, and mudstones with a low dip angle of arenites (sensu Dott, 1964) or subarkoses (sensu Folk, 1968). This stratification, attributed to wet interdunes. At the top of the sedimentary framework composition is observed at outcrops and formation are coarse sandstones and conglomerates with trough also in the subsurface samples (Gesicki, 2007). The average feldspar Author's personal copy

R. Hirata et al. / Journal of South American Earth Sciences 31 (2011) 444e456 447 content in rocks is 10.7% in eolian sandstones and 4.7% in fluvial- telodiagenesis, after the appearance of a hydraulic gradient in SAG eolian sandstones (Itirapina Sandstone) in the Pirambóia Formation with resulting penetration of meteoric waters from the recharge and 5.4% in the Botucatu Formation (Gesicki, 2007). zone in the east after uplift of Serra do Mar in Late Cretaceous time, The mineralogical composition of framework grains is one of the w65 Ma (Araújo et al., 1999; França et al., 2003); (8) authigenesis of main factors influencing the diagenetic evolution of each unit. Both kaolinite (Pirambóia Formation) and amorphous silica (Botucatu formations were buried at a relatively shallow depth (not more Formation) restricted to marginal zones of SAG in the east of São than 2000 m in the study area), with more impact on the Pirambóia Paulo state (in unconfined aquifer) and cation exchange coupled Formation than on the Botucatu Formation. The diagenetic evolu- with the dissolution of calcite at transition between unconfined tion of the Pirambóia Formation was more complex than that of the and confined zone; and (9) authigenesis of analcime (Pirambóia Botucatu Formation not only due to its older age and higher burial Formation) restricted to the confined region of SAG in the west of depth but also due to different depositional characteristics such as São Paulo state. The last two diagenetic modifications are still under major mineralogical variability linked to a higher content of clays, operation. feldspars, and accessory metamorphic minerals (Gesicki, 2007; As a consequence of sedimentary characteristics which are typical Fig. 2). of eolian deposits, such as the absence of clay matrix in sandstones, According to Gesicki (2007), the main diagenetic modifications good sorting, and high depositional porosities (theoretical values in Pirambóia and Botucatu formations (Figs. 2 and 3) were: (1) around 40%), eolian dune deposits of both formations represent an adhesion of ferrugineous clay coatings on the surface of grains; (2) excellent reservoir for groundwater. These original sedimentary infiltration of clays in the eodiagenetic stage under phreatic characteristics are generally well preserved even after diagenetic conditions (Pirambóia Formation) and vadose zone conditions transformations. This is evidenced by the high average porosity based (Botucatu Formation); (3) regeneration of clay coatings with neo- on thin sections of eolian sandstones, which is 18.9% for Pirambóia formation of smectite in the advanced eodiagenetic stage (Piram- Formation and 19.5% for Botucatu Formation (Gesicki, 2007). bóia Formation); (4) authigenesis of quartz and K-feldspar as syntaxial overgrowth on detrital grains of the same composition in 4. Hydrogeological framework and environmental isotopes the eodiagenetic stage (Itirapina Sandstones) and mesodiagenetic stage (eolian deposits of Pirambóia and Botucatu formations); (5) In this section, potentiometric and isotopic data together with bitumen cementation in the mesodiagenetic stage (Pirambóia aquifer geometry are discussed to develop the conceptual flow Formation); (6) cementation by interstitial calcite in the meso- pattern model. The SAG in São Paulo state comprises a relatively diagenetic stage and telodiagenetic stage (Pirambóia Formation); small outcrop zone in the east (about 10% of total SAG area), where (7) formation of secondary porosity by the dissolution of the the aquifer is unconfined, and a much larger confined zone (90% of unstable mineral framework (feldspars and rock fragments) during total SAG area), reaching 190,000 km2 (DAEE, IG, IPT, CPRM, 2005),

Fig. 2. Comparison chart of the diagenetic events recognized for Pirambóia (PIR) and Botucatu (BOT) formations in São Paulo state (Gesicki, 2007). PeTr: Permian to Triassic; J/KeKi: Jurassic/Cretaceous to Early Cretaceous; KieKs; Early to Late Cretaceous; KseRecent: Late Cretaceous to Recent. Author's personal copy

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Fig. 3. Petrographic images of Pirambóia and Botucatu formations illustrating the diagenetic events. A) Bimodal texture of framework grains (grain size modes of medium- and fine- grained sand), typical of dune eolian deposits. Note the open packing of the framework where intergranular plain grain contacts predominate. Core sample of Botucatu Formation, Araçatuba well, 1080 m depth. B) Moldic pore (m) and intragranular pore in lithic fragment (l). Intergranular pore space is partially filled with kaolinite booklets (k). Cutting sample of the Pirambóia Formation, Santa Rosa de Viterbo well, 100 m depth. C) Pore lining opal-CT cement in eolian deposit of the Botucatu Formation, whose occurrence is restricted to the marginal outcrop of this unit. Sample from Araraquara town quarry. D) Fluvial-eolian sandstone of upper Piramboia Formation (Itirapina sandstone) displaying blocky calcite cement (c), the preferential cemented horizon of SAG in São Paulo state. Barretos well, 900 m depth. E) SEM image (secondary electrons) of lower eolian sandstone from Pirambóia Formation showing quartz overgrowth on detrital grain. Cutting sample from Presidente Prudente well, 1795 m depth. F) SEM image (SE mode) of eolian sandstone from Pirambóia Formation with clay coatings regenerated during diagenesis, displaying typical crenulate texture, probably smectites, Pitangueiras well, 672 m depth. that is, 20% of the Brazilian portion of the SAG. The SAG over et al. (1999), for the whole extent of SAG, the hydraulic conductivity extensive areas in the interior of São Paulo exhibits artesian condi- values are 8.7 m/d in the Botucatu Formation and 1.9 m/d in the tions in deep water wells. The wells located in the SAG have the Pirambóia Formation. In contrast to high hydraulic conductivity highest yields in São Paulo state. Several wells provide more than values, average linear velocities of flow are low as a consequence of 600 m3/h (167 L/s) and up to 150 m3/h (42 L/s) in the confined and low regional hydraulic gradients (typically 0.1e0.3 m/km). unconfined portions of the aquifer, respectively. In São Paulo state, Considering effective porosity values of 15% (from 10 to 30%), the high need for water by municipalities and industry combined average linear velocity in the confined portion of the aquifer is with the good hydraulic characteristics of the aquifer is responsible 0.5 m/d, in contrast to the velocity observed in the unconfined for 70% of whole SAG groundwater exploitation (PSAG, 2009). portion, which reaches 5 m/d. High well yields are linked to high hydraulic conductivity values The recharge of the SAG in São Paulo is limited to the outcrop (Table 2). Average values of hydraulic conductivity in the SAG are zone and several stratigraphic windows (direct connection of the from 2 to 15 m/d with an average of 13.0 m/d. According to Araújo SAG with the Bauru Group due to the absence of volcanic rocks) Author's personal copy

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Table 2 4.1. Environmental isotopes Hydraulic characteristics of Guarani Aquifer System in the São Paulo state. 18 Piramboia Botucatu Environmental d O isotopes were also used to interpret the Formation Formation groundwater flow pattern in the SAG. There are three groups and Thickness (m) 75e270 20e238 two sub-groups of groundwater based on isotopic values (Fig. 4): Hydraulic conductivity (m/d) 2.5 (0.5e3) 3.5 (2e4) i) groundwater in the Recharge Zone (Zone A) close to the outcrop 3 5 Storativity (dimensionless) 1 10 e1 10 d18 > & e e are characterized by O values 7 , generally related to the Porosity (dimensionless) 0.15 (0.20 0.30) 0.25 (0.20 0.40) fi Effective porosity (dimensionless) 0.15 (0.10e0.30) modern groundwater; ii) groundwater in the Con ned Zone (Zone 18 Hydraulic gradient B) in the middle of the state is characterized with d O Confined area (m/m) 0.001 values < 7&, related to old to very old water (>10,000 years). It is Unconfined area (m/m) 0.008e0.003 important to mention that the lowest values of d18O < 9& in São Advective velocity (m/d) Paulo (and perhaps in the whole SAG) are observed in the Bauru- Confined area 0.017 0.023 Unconfined area 0.133 0.187 Agudos region. The water age was determined by Aravena (2009), 14 Recharge unconfined area (mm/a) 100e200 using C analyses. These very high values can be associated to Regional deep recharge (mm/a) 10e20 a restricted groundwater flow and limited connections between Average (max-min) this portion of the aquifer with the rest of the SAG, perhaps Source: Hirata et al. (1999); DAEE. IG. IPT. CPRM (2005); PSAG (2009); Assine et al. conditioned to the Ponta Grossa Arc in the south and some (2004). unknown structure in the western part of the state; and iii) groundwater in the Deep Confined Zone (Zone C) in the extreme west of São Paulo and in Mato Grosso do Sul is characterized by found at least in Bauru, Araraquara, and São Carlos. The recharge d18O values > 7&, representing very old water (>>10,000 years). across fractured volcanic rock of the Serra Geral Formation seems to These results are consistent with the conceptual flow model of be limited to the area close to the outcrop. According to Fernandes the SAG, where very low groundwater velocities (associated to the et al. (2006), in the region of Ribeirão Preto (NE of the state), the very low hydraulic gradient) are observed in the confined aquifer recharge occurs when there is only one flow lava event, when the (Zones B and C). The modern groundwater located near the amygdule layers are not present and the total thickness of volcanic recharge areas is characterized by d13C values around 19& rocks is less than 50 m. (Aravena, 2009), which is typical for groundwater affected by In the outcrop zone, recharge is high due to high precipitation dissolution of calcite under open system condition. Then, along the (from 1100 to 1350 mm/y, Setzer, 1966), relatively permeable groundwater flow a change toward more enriched values as high sediments, and flat topography. The estimated recharge in the area as 3.5& is observed, which is a reflection of carbonate dissolution is between 300 and 400 mm/a. However, only a small part of this under closed system condition (Table 3, see Fig. 1 for well location). amount, around 10e15 mm/yr (1e2% of the precipitation), The isotopic pattern demonstrates that the Guarani Aquifer was recharges the deep confined zone. Calculations based on Darcy’s recharged under various climatic regimes in São Paulo state, Law using equipotential lines and hydraulic conductivity values including a more humid and cold climate in the case of water of gave recharge values from 10 to 20 mm/a. Wendland et al. (2007) Zone B and climatic regimes similar to recent conditions in the case studied a small basin close to São Carlos and estimated deep of groundwater in ZA and ZC (Fig. 4). This behavior was already aquifer recharge as 40 mm/a and outcrop zone recharge as described in the SAG by Gallo and Sinelli (1980), Silva (1983), and 350 mm/a. The difference between total recharge in the outcrop Kimmelmann et al. (1995), and also in other parts of the world zone and regional deep zone recharge contributed to the losses to (Sonntag et al., 1978; Sultan et al., 1997). baseflow in rivers crossing the outcrop zone. In this way it is Due to the geometry of the SAG, the old groundwater recharged possible to distinguish a dynamic flow system in the outcrop zone under different climatic conditions as indicated by different stable and a slow flow system in the deep confined zone, where very old isotopes fingerprint described above is found in extensive areas in groundwater (>10,000 years) occurs. Due to that, old water the State of São Paulo, making the SAG in its confined portion (>5000 years) can be found much closer to the SAG outcrop a completely “storage-dominated” groundwater system, with (<30 km). important implications for water management (Foster et al., 2009). The groundwater flow in São Paulo state is relatively slow compared to the rest of the SAG and is controlled by several 5. Hydrogeochemistry geological features, which direct the flow towards the west and southwest. These features include: (a) hydraulic barrier for flow The groundwater geochemistry data permit the different types towards the south formed by the Ponta Grossa Arc (in the north of of groundwater to be divided into three main groups (with two Paraná), a tectonic structure with dikes of igneous rocks that additional sub-groups) that have already been recognized by imposes a strong anisotropy and directs the SAG flow towards the environmental isotopes (Fig. 4, Table 3). The water groups are west; (b) in the proximity of the Paraná river, the convergence with intimately associated to the aquifer flow pattern and their chemical flow coming from the north from the recharge zone in Goiás compositions are controlled by the aquifer geometry (a small (Fig. 1); (c) a zone without recharge (no flow SAG boundary) in the recharge zone and a very large portion confined by overflow north of São Paulo state caused by capping of the SAG by volcanic volcanic rock) and the SAG groundwater mixing with other deeper rocks of Serra Geral Formation; and (d) a strong confinement by groundwater associated to the pre-SAG Rio do Rastro and Teresina/ overlying volcanic rocks in 90% of the SAG area in São Paulo state. Corumbataí formations. Except for the discharge in the outcrop zone and in some The analysis of water permits the following geochemical stratigraphic windows on volcanic rocks, there are no discharge sequence to be defined: CaeHCO3 water type with lightly acid pH areas of the SAG in São Paulo state. Currently main discharge occurs (ZA1) associated with recharge zones, (ZA2) and close to recharge via pumping from more than 1500 wells with a total extraction rate zones (ZA3b) evolved to the NaeHCO3 groundwater type with of more than 2.3 Mm3/a (26.4 m3/s) (Vives et al., 2008). Main alkaline pH (ZB4a and b) in the confined zone and then pumping areas are around Ribeirão Preto, Bauru, São José de Rio to NaeHCO3/CO3eCleSO4 groundwater type, with alkaline pH (up Preto, Marília, and Araraquara. to 10) and relatively elevated Cl and SO4 concentrations (up to Author's personal copy

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Fig. 4. Groundwater groups based on d18O values and groundwater ﬂow dynamics of SAG in São Paulo state and surroundings.

130 mg/L and 99 mg/L in PRU, respectively) in the deep confined The same evolution is observed from a closed to unconfined area zone (ZC5) (Figs. 4 and 5). Groundwater ZB3b (AGU, BAU wells) (ZA2) to area ZA3 and finally to a confined area (ZB4a) in the north represents an evolution of typical unconfined zone groundwater of the Tietê river. The ZB4a and b water is also a step in between the (ZA) toward the ZB4b groundwater (PGU, MRL, TUP wells) in a more ZA2 water (MAT, JAB, SER wells), which evolves to ZC5 water (EPI, confined aquifer zone, where Na, instead of Ca, is the dominant PRU wells), following the regional main groundwater flow direction cation. (Fig. 1).

Table 3 Water chemistry and isotopic data for sampled wells.

18 13 T[C] EC [mS/cm] pH Eh [mV] Na [mg/l] K [mg/l] Ca [mg/l] Mg [mg/l] HCO3 [mg/l] CO3 [mg/l] SO4 [mg/l] Cl [mg/l] Si [mg/l] F [mg/l] d O[&] d C[&] MAT 31 253 7.47 189 2.30 6.10 41.00 4.60 147.66 bld bld bld 24.20 bld 6.7 11.3 JAB 31.4 199 7.93 191 10.00 3.10 26.00 3.30 113.49 0.62 bld bld 14.10 bld 9.4 11.0 SER 29.2 184 7.70 180 4.10 5.30 28.00 2.20 104.03 bld bld bld 20.60 bld 8.0 12.1 BAT 27.7 48 5.90 228 1.50 6.80 3.00 1.10 25.82 bld bld bld 20.60 bld 6.5 15.9 SJB 34.7 154 8.06 179 11.00 4.40 13.00 3.60 80.82 3.08 bld bld 13.80 bld 9.2 8.70 SBB 25.8 189.9 8.02 155 13.00 2.30 19.00 1.20 104.03 bld bld bld 39.60 bld 6.8 15.5 TIM 22.1 41.8 5.64 195 3.10 3.50 1.60 0.90 6.71 bld bld 1.60 26.50 bld 6.6 18.9 CAS 28.0 38.3 5.71 215 0.50 6.80 2.00 0.80 17.39 bld bld bld 19.90 bld 6.3 19.3 LSA 31.5 187.1 6.79 224 4.50 9.10 24.00 2.00 92.75 bld bld bld 20.80 bld 6.9 e BAU1 26.6 150.3 9.08 151 29.00 1.00 3.30 0.20 76.13 4.41 bld bld 14.30 bld 8.2 13.7 BAU2 27.7 149.3 9.17 134 30.00 0.90 2.60 0.10 77.75 6.15 bld bld 16.20 bld 8.3 13.2 AGU 26.4 141 8.98 140 25.00 1.40 4.70 0.40 76.24 4.31 bld bld 19.60 bld 7.5 12.4 BAR 48 342 9.11 117 74.00 0.50 1.00 bld 150.85 20.30 8.00 bld 23.80 0.20 8.4 9.20 GUA 35.6 340 9.25 168 77.00 bld 1.10 bld 162.39 20.51 6.00 bld 23.30 0.10 7.8 9.30 OLI 42.3 408 9.46 118 87.00 bld 0.80 bld 154.75 34.86 8.00 6.20 33.00 0.20 8.1 10.70 SRP 40.9 403 9.28 105 91.00 0.60 1.00 0.10 165.73 28.92 7.00 11.30 23.50 0.40 7.8 8.70 PGU 47.8 610 9.65 48 130.00 0.70 0.40 bld 240.77 54.55 8.00 6.50 100.00 1.40 8.0 5.4 MRL 43.8 511 10.01 64 106.00 0.60 0.40 bld 244.42 7.28 3.00 bld 95.60 bld 8.4 7.90 TUP 54.2 492 9.78 60 105.00 0.60 0.50 bld 236.91 4.72 6.00 3.30 62.00 0.80 8.3 6.10 FER3 57.4 538 9.29 121 105.00 1.10 1.30 bld 124.21 20.10 37.00 39.80 31.20 0.40 7.8 8.30 FER2 56.0 497 9.27 120 102.00 1.10 1.50 bld 123.56 19.07 38.00 37.80 33.80 0.50 7.9 e EPI 66.4 932.5 8.45 92 191.00 2.10 2.10 bld 265.34 9.84 78.00 53.30 38.10 5.80 6.2 7.30 PRU 58.3 1428 8.59 6 308.00 3.90 2.00 0.10 342.61 13.13 99.00 130.00 34.00 8.40 6.0 3.90 LIN 39.2 545 9.79 77 116.00 0.80 0.80 0.10 254.96 5.13 12.00 4.30 34.90 0.60 8.2 7.80 ADD 45.0 850 9.02 71 195.00 1.20 0.80 bld 341.67 27.48 31.00 22.90 24.40 2.30 6.2 5.60 ARÇ 47.7 498 9.32 77 105.00 0.70 0.90 bld 166.88 24.41 22.00 18.90 31.90 0.50 8.1 e

Bld: below limit of detection. Author's personal copy

R. Hirata et al. / Journal of South American Earth Sciences 31 (2011) 444e456 451

Fig. 5. Piper diagram showing the different groups of water in the SAG.

The presence of relatively high concentration of Cl and SO4 in It is worth mentioning that the groundwater from ADD and EPI the deep confined part of the aquifer is not only associated with wells shows lower scores for PC1 than the groundwater from the the geochemical evolution of water, following the groundwater PRU well. This is consistent with lower Na and HCO3 concentrations flow. Recent geological studies conducted by Santa Ana et al. in groundwater from the ADD and EPI wells compared to the PRU (2009) have recognized that there are two different formations well. This also suggests that the geological units tapped by the ADD below the SAG in São Paulo. From the eastern outcrop zone to the and EPI wells may not be hydraulically connected with the middle of the state, the SAG basement is underlain by sedi- geological unit tapped by the PRU well and may represent the mentary rocks of the Corumbataí/Teresina Formation and in the inflow of groundwater from the north of São Paulo state. However, western portion by rocks of the Rio do Rastro Formation. The groundwater from several wells in the left part of the graph, contact of these two units has an approximately NNWeSSE including BAU and AGU may also gradually evolve towards the PRU direction and is in between Tupã and Presidente Prudente, groundwater type. indicating that the ADD, EPI, and PRU wells are tapping the Rio The results of Hierarchical Cluster Analysis (HCA) in Ward’s Rastro formation. The influence of the units underlying the SAG is mode (Fig. 8) confirm the geochemical evolution model described observed clearly in the Na þ K map which shows the highest previously. It is possible to recognize that wells in the deep concentrations coinciding with the distribution of these two confined zone (ZC), with NaeHCO3 type water, high concentrations units (Fig. 6a). The anomalous high concentration of F (up to of SO4 and Cl, and high pH and EC values, are located in a cluster in 12 mg/L) is probably also related to this pre-SAG water (Manzano a location on the far right and the groundwater from ADD, EPI, and and Guimarães, 2008). PRU wells belong to this cluster. On the other hand, wells located The water quality distribution in these zones and sub-zones is close to the recharge zone (ZA), with CaeHCO3 type water and low also confirmed by multivariate statistics, which using just the first EC values, are located in the cluster on the left (typically associated two components of Principal Statistical Analysis, can explain with BAU, BAT, AGU, and CAS wells). The group of wells located 96.07% of the variability in the data set [Principal Component 1 between these two extremes of the graphic represents the transi- (PC1): 87.64%, PC2: 8.43%] (Fig. 7). PC1 has high loadings for EC, tion between confined and unconfined zones. HCO3, and Na and intermediate loadings for Cl and SO4, while PC2 has high loadings for Eh and Cl and an intermediate loading for SO4. 6. Geochemical modeling Comparison of the Principal Component Analysis (PCA) with water chemistry allows the PC1 high scores to be interpreted (Fig. 7)as Saturation indices for calcite are negative, indicating under- a degree of geochemical evolution towards a high pH, NaeHCO3 saturation water condition in the zone close to the aquifer outcrop groundwater type. This means that high PC1 scores indicate mature (ZA2, 3; TIM, BAU, and SER wells), evoluting to a supersaturated Na-HCO3 groundwater affected by cation exchange and dissolution condition in the deep confined zone (ZC; including PRU, EPI, and of carbonates observed in confined zone close to the Paraná river ADD wells) (Fig. 6b). The groundwater is undersaturated with and, in contrast, low PC1 scores correspond to CaeHCO3 ground- respect to dolomite and gypsum, in contrast to the positive satu- water found in unconfined zone close to recharge area. On the other ration indices for goethite and some positive saturation indices for hand, PC2 is not well defined and probably indicates a relatively kaolinite, suggesting that the latter mineral phases, when present oxidized environment with the input of Cl and SO4. as cement in sandstone, are stable. Amorphous silica saturation Author's personal copy

452 R. Hirata et al. / Journal of South American Earth Sciences 31 (2011) 444e456

Fig. 6. (a) Concentration of sodium þ potassium in the SAG, (b) saturation indices for calcite, (c) calculated values of log PCO2. Author's personal copy

R. Hirata et al. / Journal of South American Earth Sciences 31 (2011) 444e456 453

200

PRU

100 FER3 BAT CAS FER2 EPI TIM LSA

SJB JAB SER BAR GUA AGU MAT

Component 2 OLI ARC SBB SRP BAR

0 ADD LIN

PGU TUP

MRL

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 Component 1

Fig. 7. Results of Principal Component Analysis (PCA) for groundwater samples of SAG in São Paulo state. indexes are negative in the whole area, but some values for chal- issue and it is possible that discharge at pre-development stage was cedony are positive, especially in the zone close to the SAG outcrop. limited. Currently the main groundwater discharge in São Paulo This is consistent with quartz composition cement found in some state occurs via pumping wells (Foster et al., 2009). sandstone samples. On the other hand, the groundwater is unsat- The diagenetic analysis of Pirambóia and Botucatu formations urated with respect to fluorite, indicating that there is no mineral revealed that the current hydrogeochemical configuration of SAG phase controlling dissolved fluorine concentrations. Calculated log groundwater is associated with rock/water interactions in the late PCO2 values are very low (reaching 6.0) generally in the deep telodiagenetic stage (in the last 30,000 years) with active confined zone, and relatively higher values are found close to the groundwater flow through rocks previously modified by diage- recharge zone (ZA1,2), (Table 4, Fig. 6c). This suggests that there is netic events. no CO2 input in the deep confined zone as a consequence of the lack A marginal portion of SAG, which comprises outcrops of of organic matter in sediments. Pirambóia and Botucatu formations and a part of a moderately confined zone (down to a depth of 300 m) has Cae MgeHCO3 water 7. Discussion (ZA). The groundwater has low mineralization and slightly acidic or neutral pH. They are at equilibrium with kaolinite, muscovite, and The flow pattern in the SAG has its origin in the final Cretaceous smectite. In this zone, the groundwater is saturated with respect to (w65 Ma), when the emergence of the Serra do Mar in the eastern chalcedony and undersaturated with respect to calcite. These margin of the basin induced the creation of a hydraulic gradient saturation conditions are consistent with petrographic observa- and penetration of recharge with resulting flow from east to west tions, since kaolinite cement is found in samples from outcrops and (Araújo et al., 1999). From the Middle Tertiary, when the climate in from shallow wells in Pirambóia Formation (wells located in Santa the region became more humid, recharge water penetrated the Rosa do Viterbo, Santa Lúcia, São Carlos, and Orlândia). In this deep zone of the SAG and modified the hydrogeochemical char- region, the presence of secondary porosity (intraparticle and mol- acteristics, which have reached the current conditions. The dic) indicates intensive dissolution of detrital grains, especially groundwater flow pattern in São Paulo state is characterized by feldspar ones. The mineral dissolution is probably accompanied by water that infiltrates directly from precipitation in the eastern the precipitation of pore-filling kaolinite (Pirambóia Formation) or outcrop zone. Close to Fernandópolis (FER), another system brings clay replacing feldspar and precipitation of amorphous silica water from the northern portion of the SAG associated to the SAG (Botucatu Formation). Calcite cement is not found in the outcrop outcrop in Goiás. The location of discharge area is a controversial zone, but it is present in the Pirambóia Formation even in areas Author's personal copy

454 R. Hirata et al. / Journal of South American Earth Sciences 31 (2011) 444e456

Fig. 8. Hierarchical Cluster Analysis (HCA) in Ward’s mode for groundwater of SAG in São Paulo state.

Table 4 Saturation indices for selected minerals.

Well/SI calcite dolomite gypsum goethite kaolinite SiO2(a) chalcedony ﬂuorite Log PCO2 MAT 0.06 0.67 3.99 5.10 1.91 0.73 0.09 3.82 2.26 JAT 0.10 0.27 4.14 5.27 0.49 0.98 0.16 3.99 2.83 SER 0.15 1.01 4.10 5.26 1.54 0.79 0.03 3.93 2.65 BAT 3.47 7.00 4.94 1.55 3.31 0.78 0.06 4.83 1.45 SJB 0.14 0.39 4.40 5.19 0.17 1.01 0.21 4.30 3.07 GUA 0.06 0.73 4.55 5.77 1.27 0.93 0.12 4.94 4.04 BAR 0.00 0.73 4.46 4.37 1.34 1.01 0.25 4.50 3.83 OLI 0.05 0.54 4.64 4.29 1.24 0.93 0.15 4.62 4.29 SRP 0.07 0.30 4.57 6.01 1.61 1.00 0.21 3.88 4.03 FER3 0.14 0.56 3.74 3.91 2.77 1.06 0.32 3.93 4.14 FER2 0.18 0.54 3.66 3.97 2.33 1.01 0.26 3.65 4.13 CAS 3.99 8.01 5.10 0.78 2.61 0.79 0.04 5.02 1.42 LSA 1.13 2.93 4.15 5.80 3.01 0.80 0.02 4.01 1.77 ADD 0.00 0.62 4.15 4.53 2.36 0.95 0.18 2.60 3.42 ARC 0.05 0.56 4.16 4.99 1.98 0.96 0.19 3.83 4.08 EPI 0.09 0.94 3.22 4.84 1.56 0.84 0.12 1.47 2.77 PRU 0.15 0.46 3.26 4.38 2.44 0.85 0.11 1.19 2.88 PGU 0.13 0.52 5.10 3.92 1.80 0.63 0.14 3.44 4.43 MRL 0.12 0.55 5.49 4.88 2.75 0.83 0.05 6.26 5.15 TUP 0.03 0.41 5.11 3.57 3.20 1.01 0.26 3.88 4.70 LIN 0.20 0.08 4.61 4.11 2.93 1.04 0.25 3.78 4.65 BAU 0.07 0.69 4.99 5.12 1.36 1.00 0.17 4.82 4.23 AGU 0.14 0.41 4.83 5.18 0.83 0.85 0.01 4.66 4.12 SBB 0.05 0.93 4.25 5.38 1.87 0.48 0.35 4.05 3.00 TIM 4.65 9.25 5.19 0.04 2.30 0.62 0.23 5.07 1.80

Bold e supersaturation. Author's personal copy

R. Hirata et al. / Journal of South American Earth Sciences 31 (2011) 444e456 455 close to the aquifer confinement limit in Sertãozinho, Batatais, and the Rio do Rastro formations (Santa Ana et al., 2009). Comparing Matão. the geological map of the SAG basement and the presence of The geochemical changes caused by the penetration of meteoric specific ions, it is possible to associate the distinct presence of Cl waters occur at much slower velocity than the groundwater flow (>20 mg/L) and SO4 (>20 mg/L) in groundwater of the western rate. According to conservative estimate of Aráujo et al. (1999), the sector of the state with the occurrence of Rio do Rastro Formation, SAG has been flushed out at least 180 times since the penetration of suggesting the impact of pre-SAG water on the SAG. first meteoric waters. However, geochemical processes like cation One of the striking characteristics of the SAG in São Paulo state is exchange and dissolution of calcite occur at a relatively narrow the presence of the preferential calcite cementation zone on the top transition zone (Sracek and Hirata, 2002; Gastmans et al., 2010) and of the Pirambóia Formation (Itirapina Sandstones), below the are retarded compared to groundwater flow rate. The front of contact with the Botucatu Formation (Gesicki, 2007). This horizon effective mineral-leaching in Pirambóia and Botucatu formations, seems to be cemented even at the margin of SAG, where dissolution responsible for the development of significant secondary porosity of calcite should be preferred. At the Botucatu/Pirambóia interface, in marginal zones (ZA), can be localized between the area tapped by different permeability conditions should favor larger flow velocity the wells in Barretos (BAR) and São Joaquim da Barra (SJB) in and facilitate precipitation in a coarser grain size horizon, for the northern part of the state, and between the area tapped by the example, Itirapina Sandstones. On the other hand, the Botucatu wells in Bauru (BAU) and Marília (MAR) in the southern part of the Formation does not present any limitation in its porosity every- state. The zones of kaolinite precipitation in the Pirambóia where in São Paulo state, except some anomalies in Bauru. Formation and silica precipitation (opal and chalcedony) in Botu- catu Formation are restricted to the surrounding outcrop only. 8. Conclusions There are changes in the hydrogeochemical characteristics of SAG between the marginal and the deep confined (ZC) zones. These In this paper, new sedimentological, hydrogeological, and hydro- changes are related to the transformation of groundwater from geochemical data for the Guarani Aquifer System (SAG) in São Paulo CaeHCO3 type to NaeHCO3 type, caused by cation exchange state are presented and discussed. The flow direction in the north of (Sracek and Hirata, 2002). Cation exchange occurs preferentially at São Paulo state is towards the southwest due to the absence of SAG exchange sites of clays (at surface or interlayer spaces), especially outcrop in the northeast of the state. In the south, close to the Paraná smectite, with a cation exchange capacity larger than kaolinite, river and near Presidente Prudente (PPR), flow is essentially towards illite, and chlorite. Clay minerals identified in Pirambóia and the west. Both the underlying Pirambóia Formation and the overlying Botucatu formations are present as grain coatings, which were Botucatu Formation possess high porosity which was not modified regenerated during diagenesis with resulting neoformation of significantly by diagenetic changes. Several post-depositional smectite and mixed-layer illite/smectite. Due to the high content of changes have been identified, including: (1) adhesion of ferrugineous clay minerals in the Pirambóia Formation and taking into account clay coatings on the surface of grains; (2) infiltration of clays in the the facies characteristics of the unit, such as infiltrated clays and eodiagenetic stage under phreatic conditions (Pirambóia Formation) mudstone interdunes, it is reasonable to assume that the move- and vadose zone conditions (Botucatu Formation); (3) regeneration of ment of the cation exchange front in SAG is governed by sedi- clay coatings with neoformation of smectite in the advanced eodia- mentary characteristics of the Pirambóia Formation. genetic stage (Pirambóia Formation); (4) authigenesis of quartz and In the confined zone (ZC), at the depth from 500 to 1000 m, k-feldspar as syntaxial overgrowth on detrital grains of the same groundwater is of NaeHCO3 type with alkaline pH (up to 9.5) and composition in the eodiagenetic stage (Itirapina Sandstones) and low concentrations of calcium, chloride, and sulfate. In this zone, mesodiagenetic stage (eolian deposits of Pirambóia and Botucatu groundwater is in equilibrium with smectite and microcline, which formations); (5) bitumen cementation in the mesodiagenetic stage is consistent with petrographic data, indicating the presence of the (Pirambóia Formation); (6) cementation by interstitial calcite in the former mineral in grain coatings and the latter mineral in the rock mesodiagenetic stage and telodiagenetic stage (Pirambóia Forma- framework of the Pirambóia Formation. The groundwater is tion); (7) formation of secondary porosity by the dissolution of supersaturated with respect to chalcedony in the extreme north- unstable minerals (feldspars and rock fragments) during telodia- west (Fernandópolis region) and in the south (Marília region), genesis, after the appearance of a hydraulic gradient in SAG with where high dissolved silica concentrations occur. The high silica resulting penetration of meteoric waters from the recharge zone in concentrations are probably caused by intensive leaching and the east of the SAG (Araújo et al., 1999; França et al., 2003); (8) formation of intragranular porosity in the rocks of the Pirambóia authigenesis of kaolinite (Pirambóia Formation) and amorphous silica Formation, especially by leaching of feldspar grains as identified in (Botucatu Formation) restricted to marginal zones of SAG in the eastof Fernandópolis (FER1, FER2) wells. São Paulo state (in unconfined aquifer) and cation exchange/disso- In the deep confined zone of SAG in the extreme west of the lution of calcite at transition zone between unconfined zone and state, where Pirambóia and Botucatu formations are below 1000 m confined zone; and (9) authigenesis of analcime (Pirambóia Forma- depth (ZC), NaeHCO3 groundwater type with high chloride and tion) restricted to the confined region of SAG in the west of São Paulo sulfate concentrations dominates. The groundwater is in equilib- state. The last two post-depositional changes are still under operation. rium with smectite and calcite, and precipitation of calcite is The petrographic investigation of the SAG sediments confirmed favored by a high bicarbonate concentration and high pH values. a zone of chalcedony cement close to the SAG outcrop and a zone of The presence of interstitial calcite cement was confirmed in the calcite cement in the deep confined zone (Z3). This is consistent with cutting collected during drilling of the PRU well in the Pirambóia positive saturation indices for calcite and chalcedony in the confined Formation. In the same well, the Botucatu Formation is not zone (Z2) and in the zone close to the SAG outcrop (Z1), respectively. cemented, in spite of high confinement and saturation with respect The deep zone of the SAG (Z3) comprises NaeHCO3 groundwater to calcite. The sodium excess in PRU well is probably linked to the type with high 14C ages and enriched d13C values which evolved 14 hydrogeochemical characteristics of the base of the Pirambóia gradually from CaeHCO3 groundwater type with low C ages and Formation, close to the basal contact with Passa Dois Group, where depleted d13C values close to the SAG outcrop (Silva, 1983; analcime cement was identified. As mentioned before, the base- Kimmelmann et al., 1989a, b; Aravena, 2009). This seems to be ment of the SAG in the state of São Paulo is composed of two promoted by dissolution of calcite driven by cation exchange, which distinct units of the Passa Dois Group: the Corumbatai/Teresina and occurs in a relatively narrow front, moving downgradient in the Author's personal copy

456 R. Hirata et al. / Journal of South American Earth Sciences 31 (2011) 444e456 confined part of the aquifer. Some 14C ages in the deep confined zone Hirata, R.; Bastos, C.; Rocha, R., 1999. Mapeamento da vulnerabilidade e risco da close to the Paraná river are at the limit of the applicability of 14C poluição das águas subterrâneas no Estado de São Paulo. IG-SMA, CETESB, 18 DAEE. São Paulo, 2 vol. -based dating. More depleted values of dD and d O in the deep Kimmelmann, A.A., Silva, R.B.G., Reboucas, A.C., Santiago, M.M.F., 1989a. 14C analysis confined zone close to Paraná River indicate the impact of recharge of groundwater from the Botucatu Aquifer System in Brazil. Radiocarbon 31, e under a cold period climate. The SAG is a completely “storage- 926 933. ” Kimmelmann, A.A., Reboucas, A.C., Santiago, M.M.F., Silva, R.B., 1989b. Isotopic dominated system with old or very old groundwater in almost its study of the Botucatu Aquifer System in the Brazilian portion of the Paraná total extent in São Paulo state. This feature, associated with Basin, Estudios de Hidrogelogia Isotópica en America Latina, IAEA, Vienna. Tech. increasing groundwater demand, could represent a real risk of Doc 502, 51e71. Kimmelmann, A.A., Forster, M., Coelho, R., 1995. Environmental isotope and supply shortage if correct aquifer management is not applied. hydrogeochemical investigation of Bauru and Botucatu aquifers, Paraná Basin, Brazil, Estudios de Hidrogeologia Isotópica en America Latina, IAEA, Vienna. Tech. Doc 835, 57e74. Acknowledgments Kocurek, G., Havholm, K.G., 1993. Eolian sequence stratigraphy e A conceptual framework. In: Weimer, P., Possamentier, H.W. (Eds.), Siliciclastic Sequence Stratigraphy. AAPG Memoir, pp. 393e409. 58 p. The authors thank the Fundação de Amparo à Pesquisa do fi fi Lavina, E.L., 1991. Geologia sedimentar e paleogeogra a do Neopermiano Estado de São Paulo (FAPESP; grant 03/08911-0) for nancial e Eotriássico (Intervalo Kazaniano-Scythiano) da Bacia do Paraná. Porto Alegre, support of this study, the two anonymous reviewers, who IG-UFRGS, 2 vol, DSc thesis. Universidade Federal do Rio Grande do Sul. improved the quality of this manuscript, and also Marcos Antonio LEBAC, 2008. Mapa hidrogeológico do Sistema Aqüífero Guarani. Proyecto para la Protección Ambiental y Desarrollo Sostenible del Sistema Acuífero Guaraní. Netto Chamadoira for illustrations. Informe Técnico. Consorcio Guaraní, Montevideo, 57 pp. Manzano, M. and Guimarães, M., 2008. Hidroquímica regional del SAG: Estudio del origen de la composición química de las aguas subterráneas del Sistema References Acuífero Guarani. Projecto para la Protección Ambiental y Desarrollo Sostenible del Sistema Acuífero Guarani. SBCC/01/04 e 1/1018.1. Tahal Consultin Eng Ltda, Appelo, C.A.J., Postma, D., 1993. Geochemistry, Groundwater and Pollution. Taylor Seinco SRl, Hidroestruturas SA, Hidrocontrol SA, Hidroambiente SA. and Francis Books, London, 649 pp. Montevideo, Uruguay. Araújo, L.M., Franca, A.B., Potter, P.E., 1999. Hydrogeology of the Merosul aquifer Meng, S.X., Maynard, J.B., 2001. Use of statistical analysis to formulate conceptual system in the Paraná and Chaco-Paraná basins, South-America, and comparison models of geochemical behavior: water chemical data from the Botucatu with Navajo-Nugget aquifer system, USA. Hydrogeol. J. 7, 317e336. aquifer in São Paulo state, Brazil. J. Hydrology v. 250, 78e97. Aravena, R., 2009. Estúdio de la dinámica del agua subterránea en el Sistema Milani, E.J., Faccini, U.F., Scherer, C.M., Araújo, L.M., Cupertino, J.A., 1998. Sequences Acuífero Guarani (SAG) mediante técnicas isotópicas. 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