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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), B elohorská 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 (<