- Email: [email protected]
Investigation of thermoluminescence of burnt sandstones from prehistoric sites
Nuclear Instruments and Methods 175 (1980) 230-232 © North-Holland Publishing Company
INVESTIGATION OF THERMOLUMINESCENCE OF BURNT SANDSTONES FROM PREHISTORIC SITES H61~ne VALLADAS Centre des Faibles Radioactivitds, Laboratoire mixte CNRS-CEA, 91190 Gif-sur- Yvette, France
The investigation of thermoluminescence characteristics of sandstones from prehistoric fire places permits an estimate to be made of the temperature to which they have been heated.
1. Introduction
4 mg quartz aliquots (100--160 /lg) were heated at 5°C/s, using an UV filter (k = 325 nm) to investigate its TL characteristics up to 600°C or more [4]. Fig. 1A, referring to one o f the burnt sandstones, shows the glow curves o f natural TL (NTL) and NTL plus artificial TL (ATL) induced by 1.8 and 3.6 krad doses. Each curve presents two peaks at about 270 and 350°C, respectively, with TL up to 600°C. As we can see, the TL does not increase with additional irradiation above 520°C, indicating TL saturation. The TL saturation temperature varies from one sample to another. It may be assumed that above these temperatures heating in the fireplace was insufficient to erase the "geological" TL. To prove this, we extracted quartz from parts o f the samples that have not been in contact with fire and thus have not been exposed to temperatures exceeding 200°C. In these samples, we studied the gradual decrease o f the "geological" TL in relation to preheating operations in the labora-
The thermoluminescence (TL) dating, commonly applied to archaeological ceramics [1], has been extended during recent years to burnt stones from prehistoric fireplaces [2]. This work is part of an attempt to date several upperpalaeolithic sites in the the "Bassin Parisien", using quartz from siliceous sandstones. The main problem in the dating of such samples is the determination of whether the temperature in the fireplace was sufficiently high to erase the "geological" TL in the temperature interval where the glow curve is used for dating (300--400°C) [3]. The purpose of this paper is to estimate the temperature to which the sandstones had been heated.
2. Experiments Quartz grains extracted from the part o f the stone in contact with fire were used. For the measurements,
TL B
TL
+3.6 krld
0 4; 2oo 300 400 500 600 r "C Fig. 1A; Glow curves (natural and natural + 1.8 and 3.6 krad) of a sandstone heated in a prehistorical fireplace.
0
20(1
300
400
500
600
T'C
Fig. lB. Glow curves (ll .5 krad, l 3 krad, l6 krad) of a sandstone heated up to 350°C in the laboratory. 230
H. Valladas / TL of burnt sandstones
the TL emission is strongly reduced at higher temperatures and the determination of M is difficult. However, a change in the glow curve can be observed (the peak temperature is reduced from 350 to 300°C). The presence of this 300°C peak in the NTL glow curve indicates that the samples have been heated to a temperature of at least 500°C.
.\ -- ~--~ f-~-~ ~ ~'~-
440 "C
3'o0
,/oo
doo
231
66O'T'C
Fig. 1C. Ratios (R) 13/lt .5,16/13 as a function of temperature - M defines the beginning of the saturation.
tory. The samples were heated according to a temperature profile identical to that which we determined in stones placed in an experimental fireplace similar to the prehistoric ones; the heating rate was fast (10°C/s) and the cooling took a few hours. We used a 50°C-step program from 3 0 0 - 6 0 0 ° C . By measurement of the remaining "geological" TL, we found that a preheating to 350°C was sufficient for total erasure of the "geological" TL in the 300- 400°C temperature interval. A sandstone heated to 350°C in a prehistoric fireplace should be usable in TL dating. Also a sample heated to 350°C was irradiated with 1.5, 3 and 6 krad doses. Fig. 1B shows the glow curves l1,5, 13, 16, respectively. They show the same main light emission around 350°C as the glow curves obtained with the quartz sample extracted from heated sandstone (fig. 1A), while the saturation effect at high temperature is always observed. Fig. 1C presents the ratios (R) 13/11.5, 16/13 as a function of temperature. As we can see, they are constant above 440°C and approximately equal to one. The intersection M between the best line fitting the variations of R before the saturation and the straight line y = 1 defines the beginning of saturation. The average temperature at M for different preheating temperatures can be determined by the same process. The results are given in table 1. Obviously the temperature at M is about 100°C above the preheating temperature of the quartz. For preheating temperatures equal to or above 500°C,
3. Applications By determining M, the temperature can be determined to which the samples have been exposed. For example in fig. 1A (M at 520°C), the sample had been heated to 4 0 0 - 4 5 0 ° C . The same process has been used for a tenth of the sandstones from different Upper Magdalenian fireplaces such as Etiolles (Essonne), Marsangy (Yonne), Pincevent (Seine et Marne) and Verberie (Oise). The determination of the temperature at M showed that most of them had been exposed to temperatures between 350 and 450°C. The presence of the 300°C peak in the NTL of the other samples shows that they have been heated to at least 500°C.
4. Conclusion The study of the TL characteristics of quartz extracted from burnt sandstones has allowed the approximate determination of the temperature to which they had been exposed and enabled their suitability for dating to be judged. I am grateful to F. Audouze, A. Leroi-Gourhan, B. Schmider and Y. Taborin for providing the archaeological samples and to C. Lalou for her interest in this work.
References
[1] M.J. Aitken, in: Thermoluminescence of Geological
Table 1 Maximum preheating temperature (°C) Temperature at M (°C)
300 420 ± ~20
350 470 ± -20
400 500 ± -20
450 550 ± -20
XII. ARCHAEOLOGY
232
H. Valladas / TL o f burnt sandstones
materials, ed. D.J. Mc Dougall (Academic Press, New York, 1968) p. 369. [2] A.G. Wintle and M.J. Aitken, Archaeometry 19 (1977) 111. [3] S.J. Fleming, Archaeometry 12 (1970) 133.
[4] G. Valladas and H. Valladas, High temperature thermoluminescence, Proc. of the 18th Int. Symp. of Archaeometry and Archaeological Prospection (Bonn, 1978) p. 506.
INVESTIGATION OF THERMOLUMINESCENCE OF BURNT SANDSTONES FROM PREHISTORIC SITES H61~ne VALLADAS Centre des Faibles Radioactivitds, Laboratoire mixte CNRS-CEA, 91190 Gif-sur- Yvette, France
The investigation of thermoluminescence characteristics of sandstones from prehistoric fire places permits an estimate to be made of the temperature to which they have been heated.
1. Introduction
4 mg quartz aliquots (100--160 /lg) were heated at 5°C/s, using an UV filter (k = 325 nm) to investigate its TL characteristics up to 600°C or more [4]. Fig. 1A, referring to one o f the burnt sandstones, shows the glow curves o f natural TL (NTL) and NTL plus artificial TL (ATL) induced by 1.8 and 3.6 krad doses. Each curve presents two peaks at about 270 and 350°C, respectively, with TL up to 600°C. As we can see, the TL does not increase with additional irradiation above 520°C, indicating TL saturation. The TL saturation temperature varies from one sample to another. It may be assumed that above these temperatures heating in the fireplace was insufficient to erase the "geological" TL. To prove this, we extracted quartz from parts o f the samples that have not been in contact with fire and thus have not been exposed to temperatures exceeding 200°C. In these samples, we studied the gradual decrease o f the "geological" TL in relation to preheating operations in the labora-
The thermoluminescence (TL) dating, commonly applied to archaeological ceramics [1], has been extended during recent years to burnt stones from prehistoric fireplaces [2]. This work is part of an attempt to date several upperpalaeolithic sites in the the "Bassin Parisien", using quartz from siliceous sandstones. The main problem in the dating of such samples is the determination of whether the temperature in the fireplace was sufficiently high to erase the "geological" TL in the temperature interval where the glow curve is used for dating (300--400°C) [3]. The purpose of this paper is to estimate the temperature to which the sandstones had been heated.
2. Experiments Quartz grains extracted from the part o f the stone in contact with fire were used. For the measurements,
TL B
TL
+3.6 krld
0 4; 2oo 300 400 500 600 r "C Fig. 1A; Glow curves (natural and natural + 1.8 and 3.6 krad) of a sandstone heated in a prehistorical fireplace.
0
20(1
300
400
500
600
T'C
Fig. lB. Glow curves (ll .5 krad, l 3 krad, l6 krad) of a sandstone heated up to 350°C in the laboratory. 230
H. Valladas / TL of burnt sandstones
the TL emission is strongly reduced at higher temperatures and the determination of M is difficult. However, a change in the glow curve can be observed (the peak temperature is reduced from 350 to 300°C). The presence of this 300°C peak in the NTL glow curve indicates that the samples have been heated to a temperature of at least 500°C.
.\ -- ~--~ f-~-~ ~ ~'~-
440 "C
3'o0
,/oo
doo
231
66O'T'C
Fig. 1C. Ratios (R) 13/lt .5,16/13 as a function of temperature - M defines the beginning of the saturation.
tory. The samples were heated according to a temperature profile identical to that which we determined in stones placed in an experimental fireplace similar to the prehistoric ones; the heating rate was fast (10°C/s) and the cooling took a few hours. We used a 50°C-step program from 3 0 0 - 6 0 0 ° C . By measurement of the remaining "geological" TL, we found that a preheating to 350°C was sufficient for total erasure of the "geological" TL in the 300- 400°C temperature interval. A sandstone heated to 350°C in a prehistoric fireplace should be usable in TL dating. Also a sample heated to 350°C was irradiated with 1.5, 3 and 6 krad doses. Fig. 1B shows the glow curves l1,5, 13, 16, respectively. They show the same main light emission around 350°C as the glow curves obtained with the quartz sample extracted from heated sandstone (fig. 1A), while the saturation effect at high temperature is always observed. Fig. 1C presents the ratios (R) 13/11.5, 16/13 as a function of temperature. As we can see, they are constant above 440°C and approximately equal to one. The intersection M between the best line fitting the variations of R before the saturation and the straight line y = 1 defines the beginning of saturation. The average temperature at M for different preheating temperatures can be determined by the same process. The results are given in table 1. Obviously the temperature at M is about 100°C above the preheating temperature of the quartz. For preheating temperatures equal to or above 500°C,
3. Applications By determining M, the temperature can be determined to which the samples have been exposed. For example in fig. 1A (M at 520°C), the sample had been heated to 4 0 0 - 4 5 0 ° C . The same process has been used for a tenth of the sandstones from different Upper Magdalenian fireplaces such as Etiolles (Essonne), Marsangy (Yonne), Pincevent (Seine et Marne) and Verberie (Oise). The determination of the temperature at M showed that most of them had been exposed to temperatures between 350 and 450°C. The presence of the 300°C peak in the NTL of the other samples shows that they have been heated to at least 500°C.
4. Conclusion The study of the TL characteristics of quartz extracted from burnt sandstones has allowed the approximate determination of the temperature to which they had been exposed and enabled their suitability for dating to be judged. I am grateful to F. Audouze, A. Leroi-Gourhan, B. Schmider and Y. Taborin for providing the archaeological samples and to C. Lalou for her interest in this work.
References
[1] M.J. Aitken, in: Thermoluminescence of Geological
Table 1 Maximum preheating temperature (°C) Temperature at M (°C)
300 420 ± ~20
350 470 ± -20
400 500 ± -20
450 550 ± -20
XII. ARCHAEOLOGY
232
H. Valladas / TL o f burnt sandstones
materials, ed. D.J. Mc Dougall (Academic Press, New York, 1968) p. 369. [2] A.G. Wintle and M.J. Aitken, Archaeometry 19 (1977) 111. [3] S.J. Fleming, Archaeometry 12 (1970) 133.
[4] G. Valladas and H. Valladas, High temperature thermoluminescence, Proc. of the 18th Int. Symp. of Archaeometry and Archaeological Prospection (Bonn, 1978) p. 506.