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Geochemical and isotopic characteristics of spring and groundwater in the State of São Paulo, Brazil
Journal o f Hydrology, 54 (1981) 23--32
23
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
GEOCHEMICAL AND ISOTOPIC CHARACTERISTICS OF SPRING AND G R O U N D W A T E R I N T H E S T A T E O F S.~O P A U L O , B R A Z I L
M. SZIKSZAY 1, J.-M. TEISSEDRE2 , U. BARNER 3 and E. MATSUI4 11nstituto de Geociencias, Universidade de SSo Paulo, SSo Paulo (Brazil) 2 Companhia de Tecnologia de Saneamento Ambiental, C.E.T.E.S.B., $5o Paulo (Brazil) a T A H A L Consulting Engineers, Tel Aviv (Israel) 4 Centro de Energia Nuclear na Agricultura, Piracicaba (Brazil)
(Accepted for publication April 16, 1981)
ABSTRACT Szikszay, M., Teissedre, J.-M., Barner, U. and Matsui, E., 1981. Geochemical and isotopic characteristics of spring and groundwater in the State of S~o Paulo, Brazil. In : W. Back and R. L~tolle (Guest-Editors), Symposium of Geochemistry of G r o u n d w a t e r - 26th International Geological Congress. J. Hydrol., 54: 23--32. A study of spring water shows that a correlation exists between the physical and chemical characteristics of the water and the lithology from where it issues. Water from crystalline rock can be classified as Ca--Mg-bicarbonate, with low conductivity and temperature; water from sediments and]or weathered crystalline rock as Ca--Mg-chloride--sulfate; and from volcanic rock, diabase and basalt as Na-bicarbonate water. Monthly samples of eight springs and of rain water in the region of .~guas da Prata were analyzed for the deuterium and 80 isotopic contents expressed as ~D and ~ 180 in order to determine the origin of these waters. The coincidence of the isotopic values of spring water with the regional meteoric line indicates a local source of recharge. Chemical anomalies of groundwater in the shallow Bauru and Basalto aquifers in the Parand Basin are probably caused by ascending water from the confined deep Botucatu--Piramboia aquifer through fracture and fault zones. GEOLOGY OF THE STATE OF S.~O PAULO A b o u t 25% o f the State o f S~o Paulo is c o v e r e d b y o u t c r o p s o f the crystalline b a s e m e n t . T h e r e m a i n i n g area is c o v e r e d b y s e d i m e n t a r y r o c k s o f t h e Paran~ Basin a n d the small T e r t i a r y basins o f S~o Paulo a n d T a u b a t 6 , plus o t h e r r e s t r i c t e d z o n e s o f coastal s e d i m e n t s a n d alluvial deposits. T h e crystalline b a s e m e n t is c o m p o s e d o f igneous a n d m e t a m o r p h i c r o c k s such as granite, gneiss, phyllite, schist a n d q u a r t z i t e . These P r e c a m b r i a n r o c k s e x t e n d in a strip e n c o m p a s s i n g t h e c o a s t o f S~o Paulo with a w i d t h o f 100 k m a n d a length o f 4 8 0 km. The m a j o r i t y o f t h e springs s t u d i e d are in this strip, principally in t h e n o r t h e a s t e r n p a r t o f the State. Triassic--Jurassic s a n d s t o n e o f the B o t u c a t u - - P i r a m b o i a F o r m a t i o n c r o p s o u t in an area o f 1 7 , 0 0 0 k m : and has a t h i c k n e s s o f 300 m. In t h e Early C r e t a c e o u s , several d o z e n basaltic lava flows o c c u r r e d , a c c u m u l a t i n g t o a
0022-1694/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
AN~"
G~chemicoI onomoIlesOlXI probable fault areas,
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LIMITS OF PARANABASIN
%
7"
0
z0
,.o
I
so
so
STUDY AREA
-
h6OK.
415' . -
Fig. 1. Geologic map of Sao Paulo, Brazil, showing locations of geochemical anomalies and springs.
I
Sholes-Estrodo Nova Group
~
I
Sondstones-Sotu¢otuFOrmotion I~l Sp¢inQ 3 Number of spring m region
~
Pre-Combrlan-CrystoHines
Bosalt*Serro Gerol Formation ~
~
A~koli eocks
Sondstones*Sauru Group
Sondstones-FurnasFormation
Sandstones end sills TuborSo Group
Sli'
D
[~
~
sediments
]Tertiary
Legend [~
0
0
~ - - ] Ouoternoey sediments
¢
0
0
5~°
25
thickness of 1600 m which comprises the Serra Geral Formation. The Botucatu--Piramboia Formation together with the Serra Geral Formation represent the S~o Bento Group, which was covered by the Bauru Group in the Late Cretaceous. The Bauru Group consists of sandstone, clayey sandstone or siltstone with, or without, carbonate cement. These sediments crop out in an area of l 0 s km 2 and reach a m a x i m u m thickness of 300 m. The Botucatu --Piramboia Formation, the Basalto and the Bauru Group constitute the principal regional aquifers which extend t h r o u g h o u t the entire Parana Basin.
CLASSIFICATION OF CHEMICAL C H A R A C T E R OF SPRING WATER
The studied springs discharge from almost all of the geological formations within the State of S~o Paulo, from the crystalline rocks to the sediments of the Paran~ Basin (Fig. 1). Most of the springs, 43 in number, are from the magmatic and metamorphic rocks of the Crystalline Complex, nine from the sediments of the Parana Basin, and one spring is in Tertiary sediments of the
[ Q~ Alluvium ~ . ' . Sandstone __~.~ Siltite - Shale
~
Volcanicbreccia and tufts
Tinguoite ~Phonolite
............. ~ Oiobose ~
rystalline Basement
r
Spring and isotope relation
- ~ - Fault / / f ~ Inferredfault / Route frail way /~ River
Fig. 2. Geologic map of/~guas da Prata and 5 is O-values for sampled springs.
26
S~o Paulo Basin. Of these last ten springs, seven are from deep sources. The springs of Aguas da Prata, for which the isotopic analyses were made, issue from volcanic rocks and silicified sandstone (Fig. 2). The great majority of samples (Fig. 3) can be classified as Mg-bicarbonate with Ca being the cation of secondary importance; this water is associated with granite, granodiorite, gneiss and migmatite, and minor amounts of quartzite, schist and micaschist, representing Group I. In Group II, water of sediments and weathered crystalline rock can be designated as predominantly Mg-chloride--sulphate (Fig. 3). Group III can be classified as Na-bicarbonate or mixed waters issuing predominantly from granitic rock, except for analyses 31 and 30 (Aguas da Prata) which are of water from silicified sandstone. Water of Group IV is designated as Na-bicarbonate and discharges from volcanic rock, diabase and phonolite, and from sandstone interbedded with basalt. The scattered numbers correspond to volcanic rock mixed with sandy sediment and basalt, classified as bicarbonate water. Samples 72, 73 and 74 (Aguas de S~o Pedro) are sodium chloride water from sandstone and shale and are the deepest springs of the Paran~ Basin. /Oo \c~o
I00
.~
Ca
CI+NO 3
~
I00
Fig. 3. Chemical character of spring water grouped according to four hydrogeologic units, S~o Paulo, Brazil.
27 Of those samples with C a / M g < l , 73% are of water from granite and gneiss, 17% from sandy sediment and the remaining 10% from volcanic rocks. For values of Ca/Mg > 1 , 69% are of water from gneiss and migmatites and the remaining samples from rocks such as quartzite, with dolomitic limestone and sandstone. Where Ca/Mg>2, 53% of the samples are of other types of metamorphic rock and the remaining 46% from basaltic and diabasic rock associated with sandstone.
ISOTOPIC STUDY OF SPRINGS I N / ~ G U A S DA P R A T A
Monthly samplings were made of eight springs from May 1978 to April 1979. During the same period rain water was also collected. The 51SO determinations were made by the isotopic equilibrium methods between H20 and CO2 (Epstein and Mayeda, 1953), with small modifications. The 5D-values were determined according to the method described by Friedman (1953) and Friedman and Hardcastle (1970). All values are referred to the SMOW standards (Craig, 1961) and the analytical deviation are less than 0.200/00 for 51SO and 20/00 for 5D. The correlation line of rain water of Aguas da Prata (SD = 8.95180 + 20) is different from the one obtained by Craig (1961) for data which were collected principally in the northern hemisphere (SD = 851SO + 10). Alignment of the 5D and 6180 of the spring-water samples with the regional meteoric line (Fig. 4) indicates that the spring water is of meteoric origin. Isotopic data on the springs (Table I) indicate that only small monthly variations of 518 O occur in spite of the great isotopical variation in rainwater; thus, it is concluded that the volume of mixing within aquifers is 40"%o -18
-16
-14
t
I
-12 I
-10
-8
-6
I
I
I
o Rain water • Spring water
-4 i
oo
o o
-2 I
0
- -20
oo o • °.1~1
~.-r.. oo
. . ~ r n ." .-'.-
-
-40
-
-60
•
o
a -
-80
--100 o
0
--120
--140
Fig. 4 Deuterium and oxygen isotopic content of water from s p r i n g s a n d rainfall in S~o Paulo, Brazil.
- 60
Mean values
8.9
--9.0 --9.0 --8.5 --9.0 9.2 9.1 --8.4 8.9 9.1 8.7 --9.3
F. = fonte, Portuguese for spring.
--60 --60 --62 61 --59 56 -61 --58 --63 61 --59
58
59 --60 - 59 59 57 --60 --56 63 54 --57 -58
8.9
-9.0 9.2 8.8 8.8 --8.9 9.0 8.6 9.1 --8.7 --8.4 9.0
8)'80
6D
8D
8180
F. Platina
F. Paiol
May 25, 1978 Jun. 24,1978 Sep. 2, 1978 Sep. 30, 1978 Oct. 21, 1978 Nov. 18, 1978 Dec. 16, 1978 Jan. 26,1979 Feb. 17,1979 Mar. 18, 1979 Apr. 6, 1979
Date of sampling
--47
48 --47 --49 --48 --47 52 --46 --44 --45 43 --46
6D
7.3
7.2 --7.5 --7.6 7.5 7.6 7.4 --7.3 --7.1 7.1 6.7 - 7.5
8180
F. PrataRadioativa
45
--45 --43 45 - 45 - 43 --47 45 45 -45 --43 48
7.1
7.4 --7.1 6.7 --7.1 --6.9 7.3 --6.7 - 7.2 --7.1 7.5 7.2
--56
57 --53 56 --55 59 56 --58 --57 54 58 --54
8D
8D
8180
F. PrataAntiga
F. ViUela
Values of 5D (°/co) and 8180 (°/0o) in w a t e r samples f r o m springs, S~o Paulo, Brazil
TABLE I
57
--53 --58 57 - 58 --56 -56 --58 -57 --58 57 56
--8.7 --8.6 --8.1 --8.6 8.9 --8.6 8.4 --8.5 --8.7 9.4 8.6
8.7 "
8D
8180
F. PrataNova
--8.5
--7.6 --8.7 --8.2 --8.7 --8.7 8.6 8.4 --8.8 --8.5 8.8 8.6
8180
--52
--48 --52 --52 51 --55 --49 --54 54 --54 50 --53
8D
--8.1
--8.2 7.9 --8.2 --7.9 --8.1 --8.1 8.3 --8.0 --8.2 --7.7 - 8.1
8180
F. Vitdria
--48
--51 --49 --49 --51 --52 --42 --47 --50 --46 --49 --47
6D
--7.7
--8.0 --7.9 --7.9 --7.7 --7.7 --7.7 --7.5 --7.6 7.4 --7.4 --7.5
8180
F. do Boi
to Go
29 relatively great. The three formations have characteristic values of 51SO as follows: (a) volcanic breccia and tufts (51sO = --8.9°/00), (b) sandstones (~lSo = --7.1°/00); and (c) diabases (51SO -- --7.7 to --8.70/00).
HYDROGEOLOGY OF THE MAIN AQUIFERS The Botucatu--Piramboia aquifer occurs within the areas of outcrops of sandstone around the margins of the Parana Basin, dipping toward the central axis of the sedimentary basin, from an altitude of 500--600 m down to 600--800 m below sea level in the subsurface near Rio Paranfi. The Botocatu aquifer seems to be continuous all along the subsurface of the basin. The Botucatu--Piramboia aquifer is confined by underlying impermeable argillaceous layers, and by thick basalt layers which overlie the sandstone. It is recharged directly by rainfall and rivers t h a t traverse the sandstone outcrops. Drainage of the Botucatu--Piramboia aquifer is still a controversial question because it has no obvious outlet. It is possible, however, t h a t small volumes of water discharge into the overlying basalts in the central parts of the sedimentary basin, and in zones of fractures and faults. Although the Basalto aquifer is heterogeneous in its lithology and hydrogeological parameters it can be considered as a regionally continuous aquifer because its great thickness and extention facilitates hydrologic interconnection between the different layers. Generally, it has a low permeability, but can have a relatively high permeability in fractures and fault zones. The basalt is covered in large part by the Bauru Formation, which forms the third and the most extensive upper aquifer of the Paran~i Basin. Because of the argillaceous and silty material the Bauru forms only a moderately permeable aquifer. In some areas, especially in the southwestern part of the basin, the Bauru Formation passes into a more coarse composition. The Bauru is cut down to the basaltic bedrock by the major rivers that traverse the basin and drain the aquifer.
HYDROGEOCHEMICAL CHARACTERISTICS OF THE WATER OF THE MAIN AQUIFERS In the confined Botucatu--Piramboia aquifer the water has high total dissolved solids (TDS) contents with a relatively high concentration of sodium, chloride and sulfate (Table II). The pH is slightly acidic in the replenishment areas and generally basic in the downgradient parts of the aquifer. The temperature of the water is proportional to the geothermal gradient and increases up to 63°C at a depth of 1 4 5 0 m (Barner and Teissedre, 1980). The groundwater of the Botucatu--Piramboia aquifer is typically Ca-bicarbonate. In the confined artesian and subartesian parts, the water changes into a Nabicarbonate or Na~arbonate type, depending on the pH-value, which varies from slightly to highly basic.
25.6 23.6 23.8 24.5 23.0 63.0 24.0 24.5
Bauru Bauru Basalto Botucatu Botucatu Botucatu (confined) Bauru .2 Basalto .2
6.1 6.2 7.7 6.8 7.0 8.7 9.7 9.5
pH (in laboratory)
• 1 Expressed as CaCO3. • 2 Water showing chemical anomalies.
Temp. (°C)
Aquifer
190 200 250 25 127 850 360 710
Conductivity (pS/em)
Typical analyses of g r o u n d w a t e r in the Paran~ Basin, Brazil
T A B L E II
159 162 212 24 92 615 254 535
TDS
{rag/l)
83 94 158 10 48 20 45 32
HCO3 .1 0 0 0 0 0 193 73 48
0.5 3.0 2.5 1.0 5.5 125.0 3.5 16.5
CO3 *l C1 0 0 0 0 2 104 58 188
SO 4 0.34 0.17 0.21 0.10 0.10 11.6 0.53 8.20
F
21.6 14.0 38.4 2.0 12.0 4.7 0.8 5.6
Ca
5.0 2.3 8.5 1.0 6.0 1.8 0 0.5
Mg
5.0 20.4 12.8 0.2 1.7 230.0 73.0 158.0
Na
3.8 5.0 2.5 0.4 1.8 2.1 0.4 1.0
K
18.8 69.0 51.0 12.0 22.0 33.0 37.0 39.0
SiO2 0 0 0 0 0 2,230 8 32
B (ug/l)
¢.0
31
In the Bauru aquifer the water can be classified into two main groups: (1) Ca-bicarbonate; and ( 2 ) m a i n l y Na-bicarbonate and subordinately Cabicarbonate. The water in the Basalto is generally similar to those of the Bauru aquifer with the only difference being the predominance of Mg in relation to Ca. This classification demonstrates the chemical similarity of the water from the three aquifers; nevertheless, there is a clear evolution of the geochemical characteristics of the water in the confined aquifer resulting from changes in the sodium chloride and sulfate content. Because of these and associated geochemical differences, anomalies in the shallow aquifers can be used as an indicator of the presence of ascending deep water through fractures of faults zones.
CHEMICAL ANOMALIES
The chemical character of water from several boreholes in the Basalto and Bauru is similar to the water of the Botucatu--Piramboia aquifers. Plotting different physicochemical elements on maps shows the existence of zones with relatively high concentrations of salts in water of Bauru and Basalto aquifers. Zones with TDS above 250 rag/1 in the Bauru and Basalto coincides with geochemical anomalies of other elements. The TDS t h a t is high in relation to the " n o r m a l " water of those aquifers is due mainly to increased concentration of the bicarbonate, sulfate, chloride and sodium. Beside these characteristics, higher concentration of other elements such as fluoride and boron has been noted. These elements are also present in the deep water of the Botucatu--Piramboia aquifer. In addition higher than normal regional temperatures and either neutral or highly basic pH were measured in the Bauru and Basalto aquifers in the anomaly zones. The observed geochemical and physical anomalies (Fig. 1) show an alignm e n t along two principal axes oriented N--S and E--W. The E--W axis coincides with the line of the Rio Grande River along ~ 1 5 0 km in the State. T h e N--S axis begins in the north at the curve of Rio Grande extending over a distance of ~ 3 0 0 km until encountering an inflection of Rio Tiet~ in the south. Judging by the composition of water encountered in the shallow aquifers, which resemble the deep water of the Botucatu, it is possible t h a t great fractures exist in the Basalto with a vertical extension of 400--500 m. These fractures probably permit a vertical ascending circulation of water from the Botucatu into the Bauru aquifer. The ascending warm water may become enriched with constituents in the Basalto and cause secondary mineralization. Indications of tectonic disturbance exist at the Kio Tiet~ alignment within the anomaly zone. It was confirmed through drilling that a difference of 200 m exists in thickness of the basalt between the two margins of the river,
32
and well logs show a strong local stratigraphic u n c o n f o r m i t y where the Bauru Formation is in direct contact with Permian sediments. The map of water levels in the Botucatu aquifer also shows a strong inclination in the gradient toward the anomaly zone along the Rio Tiet6, strengthening the hypothesis of drainage of the lower confined aquifer into fracture and fault zones in the shallow aquifers.
ACKNOWLEDGEMENTS
The authors wish to express their gratitude for the grant received from the National Commission of Nuclear Energy (C.N.E.N), Foundation for the Development of Research in the State of Sa5 Paulo (F.A.P.E.S.P.) and the National Council of Scientific and Technical Development.
REFERENCES Bamer, U. and Teissedre, J.-M., 1980. Geochemistry and high temperatures of groundwater in the Paran~ Basin deep sandstone aquifer. Commun. 26th Int. Geol. Congr. Paris. Craig, H., 1961. Standard for reporting concentrations of deuterium and oxygen-18 in natural water. Science, 133: 1833--1934. Epstein, S. and Mayeda, T., 1953. Variation of 1So content of waters from natural sources. Geochim. Cosmochim. Acta, 4 : 213--224. Friedman, I., 1953. Deuterium content of natural water and other substances. Geochim. Cosmochim. Acta, 4: 89--103. Friedman, I. and Hardcastle, K., 1970. A new technique for pumping hydrogen gas. Geochim. Cosmochim. Acta, 34: 125--126.
23
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
GEOCHEMICAL AND ISOTOPIC CHARACTERISTICS OF SPRING AND G R O U N D W A T E R I N T H E S T A T E O F S.~O P A U L O , B R A Z I L
M. SZIKSZAY 1, J.-M. TEISSEDRE2 , U. BARNER 3 and E. MATSUI4 11nstituto de Geociencias, Universidade de SSo Paulo, SSo Paulo (Brazil) 2 Companhia de Tecnologia de Saneamento Ambiental, C.E.T.E.S.B., $5o Paulo (Brazil) a T A H A L Consulting Engineers, Tel Aviv (Israel) 4 Centro de Energia Nuclear na Agricultura, Piracicaba (Brazil)
(Accepted for publication April 16, 1981)
ABSTRACT Szikszay, M., Teissedre, J.-M., Barner, U. and Matsui, E., 1981. Geochemical and isotopic characteristics of spring and groundwater in the State of S~o Paulo, Brazil. In : W. Back and R. L~tolle (Guest-Editors), Symposium of Geochemistry of G r o u n d w a t e r - 26th International Geological Congress. J. Hydrol., 54: 23--32. A study of spring water shows that a correlation exists between the physical and chemical characteristics of the water and the lithology from where it issues. Water from crystalline rock can be classified as Ca--Mg-bicarbonate, with low conductivity and temperature; water from sediments and]or weathered crystalline rock as Ca--Mg-chloride--sulfate; and from volcanic rock, diabase and basalt as Na-bicarbonate water. Monthly samples of eight springs and of rain water in the region of .~guas da Prata were analyzed for the deuterium and 80 isotopic contents expressed as ~D and ~ 180 in order to determine the origin of these waters. The coincidence of the isotopic values of spring water with the regional meteoric line indicates a local source of recharge. Chemical anomalies of groundwater in the shallow Bauru and Basalto aquifers in the Parand Basin are probably caused by ascending water from the confined deep Botucatu--Piramboia aquifer through fracture and fault zones. GEOLOGY OF THE STATE OF S.~O PAULO A b o u t 25% o f the State o f S~o Paulo is c o v e r e d b y o u t c r o p s o f the crystalline b a s e m e n t . T h e r e m a i n i n g area is c o v e r e d b y s e d i m e n t a r y r o c k s o f t h e Paran~ Basin a n d the small T e r t i a r y basins o f S~o Paulo a n d T a u b a t 6 , plus o t h e r r e s t r i c t e d z o n e s o f coastal s e d i m e n t s a n d alluvial deposits. T h e crystalline b a s e m e n t is c o m p o s e d o f igneous a n d m e t a m o r p h i c r o c k s such as granite, gneiss, phyllite, schist a n d q u a r t z i t e . These P r e c a m b r i a n r o c k s e x t e n d in a strip e n c o m p a s s i n g t h e c o a s t o f S~o Paulo with a w i d t h o f 100 k m a n d a length o f 4 8 0 km. The m a j o r i t y o f t h e springs s t u d i e d are in this strip, principally in t h e n o r t h e a s t e r n p a r t o f the State. Triassic--Jurassic s a n d s t o n e o f the B o t u c a t u - - P i r a m b o i a F o r m a t i o n c r o p s o u t in an area o f 1 7 , 0 0 0 k m : and has a t h i c k n e s s o f 300 m. In t h e Early C r e t a c e o u s , several d o z e n basaltic lava flows o c c u r r e d , a c c u m u l a t i n g t o a
0022-1694/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
AN~"
G~chemicoI onomoIlesOlXI probable fault areas,
--
I A__
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4 ~ '
+
t
+ /+,
+
+
+
+
+
+
+
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~- +
48" I
+
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+
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+
+
+
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+_ ~
+
;
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+-'~ ÷
0
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LIMITS OF PARANABASIN
%
7"
0
z0
,.o
I
so
so
STUDY AREA
-
h6OK.
415' . -
Fig. 1. Geologic map of Sao Paulo, Brazil, showing locations of geochemical anomalies and springs.
I
Sholes-Estrodo Nova Group
~
I
Sondstones-Sotu¢otuFOrmotion I~l Sp¢inQ 3 Number of spring m region
~
Pre-Combrlan-CrystoHines
Bosalt*Serro Gerol Formation ~
~
A~koli eocks
Sondstones*Sauru Group
Sondstones-FurnasFormation
Sandstones end sills TuborSo Group
Sli'
D
[~
~
sediments
]Tertiary
Legend [~
0
0
~ - - ] Ouoternoey sediments
¢
0
0
5~°
25
thickness of 1600 m which comprises the Serra Geral Formation. The Botucatu--Piramboia Formation together with the Serra Geral Formation represent the S~o Bento Group, which was covered by the Bauru Group in the Late Cretaceous. The Bauru Group consists of sandstone, clayey sandstone or siltstone with, or without, carbonate cement. These sediments crop out in an area of l 0 s km 2 and reach a m a x i m u m thickness of 300 m. The Botucatu --Piramboia Formation, the Basalto and the Bauru Group constitute the principal regional aquifers which extend t h r o u g h o u t the entire Parana Basin.
CLASSIFICATION OF CHEMICAL C H A R A C T E R OF SPRING WATER
The studied springs discharge from almost all of the geological formations within the State of S~o Paulo, from the crystalline rocks to the sediments of the Paran~ Basin (Fig. 1). Most of the springs, 43 in number, are from the magmatic and metamorphic rocks of the Crystalline Complex, nine from the sediments of the Parana Basin, and one spring is in Tertiary sediments of the
[ Q~ Alluvium ~ . ' . Sandstone __~.~ Siltite - Shale
~
Volcanicbreccia and tufts
Tinguoite ~Phonolite
............. ~ Oiobose ~
rystalline Basement
r
Spring and isotope relation
- ~ - Fault / / f ~ Inferredfault / Route frail way /~ River
Fig. 2. Geologic map of/~guas da Prata and 5 is O-values for sampled springs.
26
S~o Paulo Basin. Of these last ten springs, seven are from deep sources. The springs of Aguas da Prata, for which the isotopic analyses were made, issue from volcanic rocks and silicified sandstone (Fig. 2). The great majority of samples (Fig. 3) can be classified as Mg-bicarbonate with Ca being the cation of secondary importance; this water is associated with granite, granodiorite, gneiss and migmatite, and minor amounts of quartzite, schist and micaschist, representing Group I. In Group II, water of sediments and weathered crystalline rock can be designated as predominantly Mg-chloride--sulphate (Fig. 3). Group III can be classified as Na-bicarbonate or mixed waters issuing predominantly from granitic rock, except for analyses 31 and 30 (Aguas da Prata) which are of water from silicified sandstone. Water of Group IV is designated as Na-bicarbonate and discharges from volcanic rock, diabase and phonolite, and from sandstone interbedded with basalt. The scattered numbers correspond to volcanic rock mixed with sandy sediment and basalt, classified as bicarbonate water. Samples 72, 73 and 74 (Aguas de S~o Pedro) are sodium chloride water from sandstone and shale and are the deepest springs of the Paran~ Basin. /Oo \c~o
I00
.~
Ca
CI+NO 3
~
I00
Fig. 3. Chemical character of spring water grouped according to four hydrogeologic units, S~o Paulo, Brazil.
27 Of those samples with C a / M g < l , 73% are of water from granite and gneiss, 17% from sandy sediment and the remaining 10% from volcanic rocks. For values of Ca/Mg > 1 , 69% are of water from gneiss and migmatites and the remaining samples from rocks such as quartzite, with dolomitic limestone and sandstone. Where Ca/Mg>2, 53% of the samples are of other types of metamorphic rock and the remaining 46% from basaltic and diabasic rock associated with sandstone.
ISOTOPIC STUDY OF SPRINGS I N / ~ G U A S DA P R A T A
Monthly samplings were made of eight springs from May 1978 to April 1979. During the same period rain water was also collected. The 51SO determinations were made by the isotopic equilibrium methods between H20 and CO2 (Epstein and Mayeda, 1953), with small modifications. The 5D-values were determined according to the method described by Friedman (1953) and Friedman and Hardcastle (1970). All values are referred to the SMOW standards (Craig, 1961) and the analytical deviation are less than 0.200/00 for 51SO and 20/00 for 5D. The correlation line of rain water of Aguas da Prata (SD = 8.95180 + 20) is different from the one obtained by Craig (1961) for data which were collected principally in the northern hemisphere (SD = 851SO + 10). Alignment of the 5D and 6180 of the spring-water samples with the regional meteoric line (Fig. 4) indicates that the spring water is of meteoric origin. Isotopic data on the springs (Table I) indicate that only small monthly variations of 518 O occur in spite of the great isotopical variation in rainwater; thus, it is concluded that the volume of mixing within aquifers is 40"%o -18
-16
-14
t
I
-12 I
-10
-8
-6
I
I
I
o Rain water • Spring water
-4 i
oo
o o
-2 I
0
- -20
oo o • °.1~1
~.-r.. oo
. . ~ r n ." .-'.-
-
-40
-
-60
•
o
a -
-80
--100 o
0
--120
--140
Fig. 4 Deuterium and oxygen isotopic content of water from s p r i n g s a n d rainfall in S~o Paulo, Brazil.
- 60
Mean values
8.9
--9.0 --9.0 --8.5 --9.0 9.2 9.1 --8.4 8.9 9.1 8.7 --9.3
F. = fonte, Portuguese for spring.
--60 --60 --62 61 --59 56 -61 --58 --63 61 --59
58
59 --60 - 59 59 57 --60 --56 63 54 --57 -58
8.9
-9.0 9.2 8.8 8.8 --8.9 9.0 8.6 9.1 --8.7 --8.4 9.0
8)'80
6D
8D
8180
F. Platina
F. Paiol
May 25, 1978 Jun. 24,1978 Sep. 2, 1978 Sep. 30, 1978 Oct. 21, 1978 Nov. 18, 1978 Dec. 16, 1978 Jan. 26,1979 Feb. 17,1979 Mar. 18, 1979 Apr. 6, 1979
Date of sampling
--47
48 --47 --49 --48 --47 52 --46 --44 --45 43 --46
6D
7.3
7.2 --7.5 --7.6 7.5 7.6 7.4 --7.3 --7.1 7.1 6.7 - 7.5
8180
F. PrataRadioativa
45
--45 --43 45 - 45 - 43 --47 45 45 -45 --43 48
7.1
7.4 --7.1 6.7 --7.1 --6.9 7.3 --6.7 - 7.2 --7.1 7.5 7.2
--56
57 --53 56 --55 59 56 --58 --57 54 58 --54
8D
8D
8180
F. PrataAntiga
F. ViUela
Values of 5D (°/co) and 8180 (°/0o) in w a t e r samples f r o m springs, S~o Paulo, Brazil
TABLE I
57
--53 --58 57 - 58 --56 -56 --58 -57 --58 57 56
--8.7 --8.6 --8.1 --8.6 8.9 --8.6 8.4 --8.5 --8.7 9.4 8.6
8.7 "
8D
8180
F. PrataNova
--8.5
--7.6 --8.7 --8.2 --8.7 --8.7 8.6 8.4 --8.8 --8.5 8.8 8.6
8180
--52
--48 --52 --52 51 --55 --49 --54 54 --54 50 --53
8D
--8.1
--8.2 7.9 --8.2 --7.9 --8.1 --8.1 8.3 --8.0 --8.2 --7.7 - 8.1
8180
F. Vitdria
--48
--51 --49 --49 --51 --52 --42 --47 --50 --46 --49 --47
6D
--7.7
--8.0 --7.9 --7.9 --7.7 --7.7 --7.7 --7.5 --7.6 7.4 --7.4 --7.5
8180
F. do Boi
to Go
29 relatively great. The three formations have characteristic values of 51SO as follows: (a) volcanic breccia and tufts (51sO = --8.9°/00), (b) sandstones (~lSo = --7.1°/00); and (c) diabases (51SO -- --7.7 to --8.70/00).
HYDROGEOLOGY OF THE MAIN AQUIFERS The Botucatu--Piramboia aquifer occurs within the areas of outcrops of sandstone around the margins of the Parana Basin, dipping toward the central axis of the sedimentary basin, from an altitude of 500--600 m down to 600--800 m below sea level in the subsurface near Rio Paranfi. The Botocatu aquifer seems to be continuous all along the subsurface of the basin. The Botucatu--Piramboia aquifer is confined by underlying impermeable argillaceous layers, and by thick basalt layers which overlie the sandstone. It is recharged directly by rainfall and rivers t h a t traverse the sandstone outcrops. Drainage of the Botucatu--Piramboia aquifer is still a controversial question because it has no obvious outlet. It is possible, however, t h a t small volumes of water discharge into the overlying basalts in the central parts of the sedimentary basin, and in zones of fractures and faults. Although the Basalto aquifer is heterogeneous in its lithology and hydrogeological parameters it can be considered as a regionally continuous aquifer because its great thickness and extention facilitates hydrologic interconnection between the different layers. Generally, it has a low permeability, but can have a relatively high permeability in fractures and fault zones. The basalt is covered in large part by the Bauru Formation, which forms the third and the most extensive upper aquifer of the Paran~i Basin. Because of the argillaceous and silty material the Bauru forms only a moderately permeable aquifer. In some areas, especially in the southwestern part of the basin, the Bauru Formation passes into a more coarse composition. The Bauru is cut down to the basaltic bedrock by the major rivers that traverse the basin and drain the aquifer.
HYDROGEOCHEMICAL CHARACTERISTICS OF THE WATER OF THE MAIN AQUIFERS In the confined Botucatu--Piramboia aquifer the water has high total dissolved solids (TDS) contents with a relatively high concentration of sodium, chloride and sulfate (Table II). The pH is slightly acidic in the replenishment areas and generally basic in the downgradient parts of the aquifer. The temperature of the water is proportional to the geothermal gradient and increases up to 63°C at a depth of 1 4 5 0 m (Barner and Teissedre, 1980). The groundwater of the Botucatu--Piramboia aquifer is typically Ca-bicarbonate. In the confined artesian and subartesian parts, the water changes into a Nabicarbonate or Na~arbonate type, depending on the pH-value, which varies from slightly to highly basic.
25.6 23.6 23.8 24.5 23.0 63.0 24.0 24.5
Bauru Bauru Basalto Botucatu Botucatu Botucatu (confined) Bauru .2 Basalto .2
6.1 6.2 7.7 6.8 7.0 8.7 9.7 9.5
pH (in laboratory)
• 1 Expressed as CaCO3. • 2 Water showing chemical anomalies.
Temp. (°C)
Aquifer
190 200 250 25 127 850 360 710
Conductivity (pS/em)
Typical analyses of g r o u n d w a t e r in the Paran~ Basin, Brazil
T A B L E II
159 162 212 24 92 615 254 535
TDS
{rag/l)
83 94 158 10 48 20 45 32
HCO3 .1 0 0 0 0 0 193 73 48
0.5 3.0 2.5 1.0 5.5 125.0 3.5 16.5
CO3 *l C1 0 0 0 0 2 104 58 188
SO 4 0.34 0.17 0.21 0.10 0.10 11.6 0.53 8.20
F
21.6 14.0 38.4 2.0 12.0 4.7 0.8 5.6
Ca
5.0 2.3 8.5 1.0 6.0 1.8 0 0.5
Mg
5.0 20.4 12.8 0.2 1.7 230.0 73.0 158.0
Na
3.8 5.0 2.5 0.4 1.8 2.1 0.4 1.0
K
18.8 69.0 51.0 12.0 22.0 33.0 37.0 39.0
SiO2 0 0 0 0 0 2,230 8 32
B (ug/l)
¢.0
31
In the Bauru aquifer the water can be classified into two main groups: (1) Ca-bicarbonate; and ( 2 ) m a i n l y Na-bicarbonate and subordinately Cabicarbonate. The water in the Basalto is generally similar to those of the Bauru aquifer with the only difference being the predominance of Mg in relation to Ca. This classification demonstrates the chemical similarity of the water from the three aquifers; nevertheless, there is a clear evolution of the geochemical characteristics of the water in the confined aquifer resulting from changes in the sodium chloride and sulfate content. Because of these and associated geochemical differences, anomalies in the shallow aquifers can be used as an indicator of the presence of ascending deep water through fractures of faults zones.
CHEMICAL ANOMALIES
The chemical character of water from several boreholes in the Basalto and Bauru is similar to the water of the Botucatu--Piramboia aquifers. Plotting different physicochemical elements on maps shows the existence of zones with relatively high concentrations of salts in water of Bauru and Basalto aquifers. Zones with TDS above 250 rag/1 in the Bauru and Basalto coincides with geochemical anomalies of other elements. The TDS t h a t is high in relation to the " n o r m a l " water of those aquifers is due mainly to increased concentration of the bicarbonate, sulfate, chloride and sodium. Beside these characteristics, higher concentration of other elements such as fluoride and boron has been noted. These elements are also present in the deep water of the Botucatu--Piramboia aquifer. In addition higher than normal regional temperatures and either neutral or highly basic pH were measured in the Bauru and Basalto aquifers in the anomaly zones. The observed geochemical and physical anomalies (Fig. 1) show an alignm e n t along two principal axes oriented N--S and E--W. The E--W axis coincides with the line of the Rio Grande River along ~ 1 5 0 km in the State. T h e N--S axis begins in the north at the curve of Rio Grande extending over a distance of ~ 3 0 0 km until encountering an inflection of Rio Tiet~ in the south. Judging by the composition of water encountered in the shallow aquifers, which resemble the deep water of the Botucatu, it is possible t h a t great fractures exist in the Basalto with a vertical extension of 400--500 m. These fractures probably permit a vertical ascending circulation of water from the Botucatu into the Bauru aquifer. The ascending warm water may become enriched with constituents in the Basalto and cause secondary mineralization. Indications of tectonic disturbance exist at the Kio Tiet~ alignment within the anomaly zone. It was confirmed through drilling that a difference of 200 m exists in thickness of the basalt between the two margins of the river,
32
and well logs show a strong local stratigraphic u n c o n f o r m i t y where the Bauru Formation is in direct contact with Permian sediments. The map of water levels in the Botucatu aquifer also shows a strong inclination in the gradient toward the anomaly zone along the Rio Tiet6, strengthening the hypothesis of drainage of the lower confined aquifer into fracture and fault zones in the shallow aquifers.
ACKNOWLEDGEMENTS
The authors wish to express their gratitude for the grant received from the National Commission of Nuclear Energy (C.N.E.N), Foundation for the Development of Research in the State of Sa5 Paulo (F.A.P.E.S.P.) and the National Council of Scientific and Technical Development.
REFERENCES Bamer, U. and Teissedre, J.-M., 1980. Geochemistry and high temperatures of groundwater in the Paran~ Basin deep sandstone aquifer. Commun. 26th Int. Geol. Congr. Paris. Craig, H., 1961. Standard for reporting concentrations of deuterium and oxygen-18 in natural water. Science, 133: 1833--1934. Epstein, S. and Mayeda, T., 1953. Variation of 1So content of waters from natural sources. Geochim. Cosmochim. Acta, 4 : 213--224. Friedman, I., 1953. Deuterium content of natural water and other substances. Geochim. Cosmochim. Acta, 4: 89--103. Friedman, I. and Hardcastle, K., 1970. A new technique for pumping hydrogen gas. Geochim. Cosmochim. Acta, 34: 125--126.