Nuclear Instruments and Methods in Physics Research B 213 (2004) 751–755
www.elsevier.com/locate/nimb
Dating sediment deposits on Montalvanian carvings
using EPR and TL methods
M.D. Sastry a,1, Henry S.L. Sullasi a,*, Fabiola Camargo a,
Shigueo Watanabe a, Andre P.P. Prous b, Martha M.C. Silva
a
c
Instituto de Fısica, Universidade de S~
ao Paulo, Caixa Postal 66318 – CEP 05315-970 S~
ao Paulo, Brazil
b
Facultade de Filosofia e Ci^
encias Humanas (UFMG), Caixa Postal 1275, Beloo Horizonte, Brazil
c
Museo de Historia Natural (UFMG), Caixa Postal 1275, Beloo Horizonte, Brazil
Abstract
About 30 years ago a rock shelter with engravings by early settlers was found at Montalv^
ania, northern end of state
of Minas Gerais, Brazil. Lower part of engravings was covered with thin deposit of calcite mixed with quartz grains, due
to occasional flood. This mixture of two minerals was dated by thermoluminescence and electron paramagnetic resonance using in both cases, additive method. The accumulated dose DAC , that is, natural radioactivity and cosmic rays
radiation dose that induces TL and EPR signal intensity has been found to be around 50 Gy both by TL and EPR
methods. The annual radiation dose rate was estimated to be about 1.027 mGy/a from knowledge of uranium, thorium
and potassium content determined by inductively coupled plasma-mass spectrometer system.
The age of this calcite plus quartz deposits was estimated to be about 50 ka.
2003 Elsevier B.V. All rights reserved.
Keywords: Thermoluminescence; EPR dating; Calcite deposit; Rock carvings and defect center
1. Introduction
Both natural and laboratory irradiation can be
used in dating few millimeters thick film of calcite
plus quartz, deposited on ancient carvings made
by early settlers at Montalv^
ania extreme north of
state of Minas Gerais, Brazil. The natural radiation (from natural radioactivity and cosmic rays)
as usual created electron traps and the laboratory
radiation (gamma or beta) has been used to eval-
*
Corresponding author.
E-mail address: [email protected] (H.S.L. Sullasi).
1
On leave from Bhabha Atomic Research Center, India.
uate the energy deposited (DAC ) by natural radiation.
DAC stands for accumulated radiation dose. The
trapped electrons can be detected through luminescence stimulated either thermally (thermoluminescence – TL) or optical by (OSL). One can
also measure microwave absorption by trapped
electrons placed in a static magnetic fields (electron
paramagnetic resonance – EPR).
In the present work, TL and EPR method were
used for dating.
About 30 years ago, beautiful carvings (Fig. 1)
on rock were discovered at Montalv^ania in
northern end of Minas Gerais state Brazil [1].
These authors suggested that the carvings were
0168-583X/$ - see front matter 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0168-583X(03)01757-9
752
M.D. Sastry et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 751–755
Fig. 1. Old carving found at Montalv^ania, state of Minas Gerais, Brazil, showing thin deposit of sediments in lower part of
the picture.
artwork of very early human inhabitants in that
region. Further south in the same state of Minas
Gerais, Neves and Pucciarelli [2,3] found at Lapa
Vermelha, Minas Gerais, a female skull 11,500
years old, which was considered to be negroid type
and not mongoloid one as generally accepted for
American Indians. Prous [4] later excavated some
exotic quartz flakes which was dated between
11,680 and 15,300 before present. Guidon and
Arnard [5] and Guidon [6] reported charcoals
older than 38,000 years from archaeological site at
Pedra Furada, Serra da Capivara National Park,
Piaui state, northeastern Brazil. This National
Park is world known due to several thousands of
cave paintings. In 1990, on one of these paintings
at Toca da Bastiana was found a thin calcite strip
formed. Watanabe et al. [7] dated this calcite using
thermoluminescence and electron paramagnetic
resonance and found 33,000 years of age.
2. Experimental
Samples of sediment deposits, similar to that
shown in lower part of the picture in Fig. 1, have
been collected from several points of the engravings. Although the rock-shelter where such engravings were made is located in a hill about 60 m
of altitude, according to geologists when a very
heavy rain (storm) hits the place, the ground of
shelter is flooded. Since large area around Montalv^ania is of a calcareous soil, water from flood
deposited film of calcite on engravings. The X-ray
fluorescence analysis of the film has shown that it
contains about 32.66% SiO2 , 3.20% Al2 O3 , 63.53%
CaCO3 and several other compounds in smaller
amount. Several collected samples were numbered
to keep track of each sample used for measurements.
Hoping that high microwave power can allow
better detection of signal due to radicals from
calcite, several measurement have been carried out
at high microwave power (around 25–40 mW) and
90 out of phase with respect to 100 kHz modulating signal, at room temperature.
A part of the sample number 4 was treated in a
solution (20%) of HCl, which react with CaCO3
leaving CaO and liberating CO2 ; this was called
sample 4w. Since CaO does not produce EPR
spectrum only quartz grains left from this process
will contribute to EPR measurements. Then this
EPR result is compared with EPR spectra of nontreated sample number 4. Different microwave
power values were used for these EPR measurements as will be indicated in figures to be presented
later. In some of these measurements the spectra
were detected 90 out of phase with magnetic field
modulation signal, others not.
For TL measurements Daybreak model 1100
system was used and EPR measurements were
carried out in a Brucker Spectrometer EMS series
with ERO41KG X-band (9.75 GHz) with 100 kHz
field modulation.
3. Results and discussion
Fig. 2 shows EPR spectrum of sample number
4w irradiated to 500 Gy c-dose, taken at 25 mW
power and 90 out of phase, whereas Fig. 3 is the
spectrum of unirradiated sample under similar
condition. Fukuchi et al. [8], Fukuchi [9] and
Shimokawa and Imai [10] have found in quartz
M.D. Sastry et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 751–755
20000
150000
peroxy
center
100000
Intensity (a.u.)
10000
Intensity (a.u.)
753
0
-10000
-20000
50000
0
-50000
-100000
-30000
2.015
2.010
2.005
2.000
1.995
-150000
1.990
2.015
Factor (g)
2.010
2.005
2.000
1.995
1.990
Factor (g)
Fig. 2. EPR spectrum of sample 4w obtained using 25 mW
microwave power, 90 out of phase, irradiated to 500 Gy c-rays.
Fig. 4. EPR spectrum of sample 4w obtained using 40 mW
microwave power, in phase, irradiated to 500 Gy c-rays.
20000
peroxy
center
15000
10000
Intensity (a.u.)
Intensity (a.u.)
5000
0
5000
0
-5000
-10000
-5000
-15000
-20000
2.015
2.010
2.005
2.000
1.995
1.990
Factor (g)
2.015
2.010
2.005
2.000
1.995
1.990
Factor (g)
Fig. 3. EPR spectrum of sample 4w obtained using 25 mW
microwave power, 90 out of phase, unirradiated.
Fig. 5. EPR spectrum of sample 4w obtained using 40 mW
microwave power, in phase, unirradiated.
associated with fault movement and in volcanic
rocks in Japan EPR spectrum of peroxy (dry OHC
oxygen associated trapped hole center) and wet
OHC centers, similar to the EPR spectra obtained
in the present work at 35 mW microwave power.
At this microwave power peroxy center EPR signal is about eight time that of E10 center, Ikeya [11],
since E10 center appears also in the same region of
g-value. E10 center signal saturates around 0.1 mW
power, while peroxy center signal grows beyond
100 mW power.
Fig. 4 shows EPR spectrum of sample number
4w irradiated to 500 Gy c-rays under 40 mW in
phase, whereas Fig. 5 shows the spectrum of an
unirradiated sample with the signal from peroxy
center. This signal grows with radiation dose.
Fig. 6 present EPR spectrum of 500 Gy irradiated sample number 4 (not washed in a solution of
HCl, i.e. it contains SiO2 and CaCO3 , using 25
mW and measured 90 out of phase; Fig. 7 is that
of unirradiated sample number 4. The signal in the
region of g ¼ 2:0015 is assigned to peroxy center,
whereas the signal around g ¼ 2:005 to SO
2 center. In most of sample sulfur is found in relatively
large amount, 720–1200 ppm. Kai and Miki [12],
found SO
2 growing significantly with microwave
power, its signal saturates beyond 100 mW. Another commonly found signal coming from calcite
is CO
2 , this signal is always smaller than that of
SO
.
2 SO3 radicalÕs EPR signal becomes negligible beyond 0.1 mW power. For dating sake,
sample number 4 (calcite plus quartz grains) was
754
M.D. Sastry et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 751–755
3500
50000
40000
3000
Intensity (a.u.)
Intensity EPR (a.u.)
peroxy
center
30000
SO 2
20000
10000
0
-10000
-20000
-30000
2500
2000
1500
1000
SO 2
CO 2
Peroxy center
DAC
500
-40000
0
2.015
2.010
2.005
2.000
1.995
-100
1.990
0
100
200
300
400
500
Dose (Gy)
Factor (g)
Fig. 6. EPR spectrum of sample 4 obtained using 25 mW microwave power, 90 out of phase, irradiated to 500 Gy c-rays.
Fig. 8. EPR intensity of SO
2 , CO2 and peroxy centers as
function of radiation dose.
10000
6000
Sample 7B
5000
TL Intensity (a.u.)
Intensity (a.u.)
5000
0
-5000
4000
3000
2000
1000
DAC
-10000
2.015
2.010
2.005
2.000
1.995
1.990
Factor (g)
0
-100
0
100
200
300
400
Dose (Gy)
Fig. 7. EPR spectrum of sample 4 obtained using 25 mW microwave power, 90 out of phase, unirradiated.
Fig. 9. TL intensity of sample 7B, as function of radiation dose.
irradiated to c-rays with doses varying up to 500
Gy. Fig. 8 shows SO
2 , CO2 and peroxy center
EPR intensity as function of c-dose. The extrapolation of the curves to dose-axis yielded for DAC a
value close to 50 Gy.
For TL measurements sample number 7B has
been used. c-rays with doses of 50, 100, 200 and
400 Gy were used to irradiate sample in order to
obtain TL intensity as a function of dose, from
which an accumulated dose value of 57 ± 5 kGy
has been obtained (Fig. 9).
The annual dose rate estimation was done
measuring uranium, thorium and potassium
concentration using neutron activation analysis as
well as inductively coupled plasma-mass spectrometer (ICP-MS). For (calcite plus quartz) 0.11
ppm of uranium, 0.005 ppm of thorium and 10
ppm of potassium have been obtained. For the
rock where the engraving was made, 1.52, 0.025
and 57.88 ppm of uranium, thorium and potassium, respectively, were found. From these values
and adding cosmic rays contribution an annual
dose rate Da ¼ 1:027 0:055 mGy/a was obtained.
Therefore, for DAC of 50 Gy (by EPR) results an
age of about (48 ± 3) · 103 years, whereas for DAC
of 57.2 Gy (by TL), a little bit older age of
(55 ± 5) · 103 years is obtained.
M.D. Sastry et al. / Nucl. Instr. and Meth. in Phys. Res. B 213 (2004) 751–755
4. Conclusions
From DAC 50 Gy obtained by EPR and TL
methods an age of approximately 48 ka was obtained. With an error of about 5% in EPR measurement and of about 8% in TL measurement, an
unexpectedly old age of 55 ± 5 ka was found. This
age indicates that human inhabitants lived in
Montalv^
ania region as early as about 48,000 years
ago.
From dating calcite formation on a wall painting (Toca da Bastiana) at Parque Nacional Serra
da Capivara, Piaui state, about 650 km north of
Montalv^
ania an age of approximately 33 ka, by
TL and EPR and an age of 38.5 ka have been
obtained. This means that men lived in central
region of Brazil as early as about 50 ka.
Of course, it is necessary to find additional
dating results to confirm such an advanced age
that indicates the existence of early settlers older
than usually believe.
Acknowledgements
We would like to acknowledge following entities and persons for financial or other form of
755
contribution to the present work: FAPESP and
CNPq for financial support, Depto. de Mineralogia e Geotect^
onica of Inst. de Geoci^encia da USP
for X-rays fluorescence analysis, Instituto de Pesquisas Energeticas and Nucleares – IPEN, for irradiation and NAA of samples.
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