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Luminescence dating of a coastal Stone Age dwelling place in Northern Finland
Quaternary Science Reviews 22 (2003) 1287–1290
Luminescence dating of a coastal Stone Age dwelling place in Northern Finland K.O. Eskolaa,*, J. Okkonenb, H. Jungnera b
a Dating Laboratory, University of Helsinki, POB 64, FIN-00014 Helsinki, Finland Archaeological Laboratory, University of Oulu, POB 1000, FIN-90014 Oulu, Finland
Abstract TL and OSL methods were used in order to date an archaeologically interesting site, the Giants’ church in Kastelli, Northern Finland. The TL method was used for burnt stones collected from heaps of fire-cracked stones. At least some of the collected stones were heated properly during the times the heaps were used and that made TL dating possible. OSL measurements were made on a coastal sand layer continuing partly under the heaps. This sand layer is expected to have been formed during the same time period as the heaps were used. The results are in good agreement with radiocarbon dates on charcoal from the site and with archaeological and shoreline displacement chronology. All the results for the Kastelli site point to an age in the middle of the third millennium BC. r 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction The Giants’ church in Pattijoki Kastelli is one of the most noted archaeological sites in Northern Finland. It is located circa 60 km southwest from the town of Oulu. The site consists of several structures and archaeological features, in which the most prominent is a large rectangular stone enclosure. The size of the structure is 52 30 m2. Altogether 43 similar Giants’ church sites are known in Finland. They are all situated in the coastal area of northern Ostrobotnia. Their function is still unclear. According to isostatic land uplift and shoreline displacement chronology, they have been dated to the Stone Age. The archaeological finds found from the sites also point to the same age. The earliest studies made at the Kastelli site are from the 1860s. At 1862 one cairn was excavated, but no finds were discovered. In 1920 another excavation was made—this time the enclosure was under research. In 2001 the Finnish National Board of Antiquities arranged the survey and small-scale excavation at the Kastelli site. Mapping the site and sampling datable material was a priority. The total area of the site is approximately 3.4 ha. During the intensive surveying 43 heaps of fire-cracked stones were discovered. There are also seven dwelling depressions, most of which are the *Corresponding author.. E-mail address: kari.o.eskola@helsinki.fi (K.O. Eskola).
remains of pit houses and 19 cairns at the site. A map of the site is shown in Fig. 1. In our study we concentrated on heaps, which are most interesting for dating the site. The heaps are situated in a 150 m long band along the 52-m a.s.l. contour line. They are low mounds, which are undefined in form, and their heights range from 30 to 70 cm. The distribution marks the ancient shoreline and most likely the close access to the water was essential to the process in which the heated stones were used and the heaps were formed. The archaeological excavations clearly point to the fact that at least some of the heaps were built on the Stone Age beach. Probably, the heaps are linked to seal fat processing although the exact function of the structures is not fully understood. An earlier attempt to use heated stones from different fireplaces at Saami Winter villages in Finnish Lapland (Carpelan et al., 1992) was problematic because of relatively large difference in dating results between different fireplaces. These sites are, however, only a few hundred years old and thereby young compared to the Stone Age site at Kastelli.
2. Sampling In order to get suitable samples for dating, two of the heaps were opened (Test Pits 1 and 2 in Fig. 1). Samples of granitic stones, soil and charcoal were collected. In
0277-3791/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0277-3791(03)00077-5
1288
K.O. Eskola et al. / Quaternary Science Reviews 22 (2003) 1287–1290
The measured dose rates were relatively high. In Test Pit 1, the gamma dose rate was 1.51 mGy/a and the beta dose rate 1.89 mGy/a, giving a total dose rate of Da E3:4 mGy/a. In Test Pit 2, the gamma dose rate was 1.63 mGy/a and beta dose rate 2.19 mGy/a, giving a total dose rate of Da E3:8 mGy/a. In the coastal sand layer, the gamma dose rate was 1.33 mGy/a and beta dose rate 1.33 mGy/a, giving a total dose rate of Da E2:7 mGy/a.
4. The age of the burnt stones from the heaps
Fig. 1. Map of the Giants’ church area in Pattijoki Kastelli. The two opened heaps (Test Pits 1 and 2) are marked. The rectangular-shaped 52 30 m2 stone enclosure ‘‘the church’’ can also be seen.
addition, quartz flakes, quartz tools and some burnt animal bones (most likely of seal) were found. A clear layer (about 3–5 cm thick) of coastal sand, continuing below one of the opened heaps (Test Pit 1), was also found. Sharp-edged stones that are clearly cracked because of heating were selected for luminescence dating. Also some sand eroded from the heated stones, and thereby having the same mineralogical structure with them, was collected for beta-dose-rate measurements. Samples from the sand layer were collected from the side of the opened heap for OSL and beta-dose-rate measurements. The samples were collected carefully from different depths of the layer in order to obtain information on the time span of deposition. All samples were carefully protected from light during the collecting process. 3. Dose-rate measurements The gamma dose rate was measured at each sampling point, using a Nuclear Enterprises Ltd. PSR 8 Portable spectrometer equipped with NaI scintillation detector. Beta dose rates were measured from sand crumbled from the burned stones with a Ris^ GM-25-5 beta multicounter (B^tter-Jensen and Mejdahl, 1988). The conversion of the measured beta dose rate to absorbed dose is based on measurements on a set of samples, with known U, Th and K contents as determined by neutron activation. The conversion also includes correction for grain size and water content.
Luminescence measurements were made with an upgraded Ris^ TL-DA-12 reader (B^tter-Jensen and Duller, 1992; B^tter-Jensen et al., 1999). In total 30 stones from the heaps were collected. Half of them were from Test Pit 1 and half from Test Pit 2. The collected stones were crushed mechanically and treated with HF and HCl acid. Toyoda et al. (2000) have studied the effects of mechanical crushing on the TL signal measured from quartz samples. The results are not obvious, but in order to minimize the use of mechanical energy during the crushing operation, long etching times were preferred. From harder stones a larger scale of grain sizes were used for the same reason. Another problem was that the grains very often were polymineral containing at least quartz and feldspar. This made separation on the basis of density difficult. Also in this case longer etching times help because feldspar is removed more quickly from the grains than quartz. The purity of the separated quartz against feldspar was tested with IRSL. Some stones also contained a lot of iron. When necessary the iron was removed from samples with a magnet. The measurements were based on the regenerative dose method. Different preheat temperatures were tested and 300 C for 10 s was finally chosen. The TL signals were measured while heating the samples up to 500 C with a heating rate of 3 C/s. Background subtractions were made for each TL measurement. Natural signals were integrated over the 325 C TL peak and compared with signals from the doses given with beta source of 16.2 mGy/s after radiation times of 800, 900, 1000 and again 800 s. The difference between the first and last regenerated signal, based on the same given dose, was taken as a measure of sensitivity change. A correction assuming equal steps of sensitivity change for all heatings of the sample was applied. For a few samples the additive dose method was applied as an attempt to measure the sensitivity change between the first and second TL heating. The precision was, however, not good enough to give reliable results.
K.O. Eskola et al. / Quaternary Science Reviews 22 (2003) 1287–1290
For stones having strong dose response the sensitivity change was quite stable and the overall sensitivity change was relatively small. With some samples the shape as well as the sensitivity of the TL curve changed clearly after a couple of TL cycles was made. Results from these samples were rejected. In Table 1 absorbed doses measured for two samples each of the two opened heaps are listed. These samples have the strongest dose response and the separation between single TL results was relatively small. The errors given in Table 1, based on standard error between TL measurements made from the same sample, indicate that the equivalent dose can be measured with high precision. The main uncertainty in the age calculation stems from dose-rate determination. This uncertainty is set at around 75%. Consequently, we conclude that the stones were heated within the period 2800–2200 BC.
5. OSL results from the coastal sand The OSL measurements were made using the same Ris^ reader that was used in measurements discussed in
1289
Section 4. Quartz used for dating was density separated from the sand. The grain size used was 0.210–0.297 mm. After separation the quartz was treated with HF and HCl and used in OSL measurements based on the SAR protocol (Murray and Wintle, 2000). The absorbed dose measured from 131 single aliquot samples showed a broad distribution (see Fig. 2) with a mean value of 11.3 Gy and standard deviation 1.62 Gy. Using blindly the mean value of the natural signal would give us an age of about 4200 a. However, the distribution of the OSL measurements made from separate samples of the sand is not symmetrically Gaussian-shaped and narrow, as it should be if the sand had been completely bleached in a short time period. Instead the distribution curve is quite wide and some kind of structure can be seen. This means that there is differently bleached sand or sand bleached at different times in this sand layer. Anyhow it is possible to see that the distribution has its maximum between 4200 and 4800 yr ago. This would point to the time period 2800–2200 BC which is in good agreement with results obtained in Section 4.
Table 1 Separate TL results from two most suitable samples of burned stones from each of the opened heaps (Test Pits 1 and 2) in Kastelli site (the errors given are standard errors) Test Pit 1
Doses from separate TL measurements (Gy)
Combined doses from separate samples (Gy) Combined doses from separate Test Pits (Gy)
Test Pit 2
Sample 14
Sample 16
Sample 23
Sample 28
16.12 15.24 15.25 15.04 15.12 15.40 15.04 16.45 15.4670.19 15.3970.14
14.88 16.10 14.87 14.39 14.98 15.57 15.71 16.04 15.3270.22
15.74 14.89 17.51 15.99 19.45 17.22 18.43 17.05 17.0470.52 17.2370.27
16.73 17.91 18.11 17.51 16.99 17.26 17.44 17.50 17.4370.16
OSL results 25
Frequency
20 15 10 5 0 0
1000
2000
3000
4000
5000
6000
Age [a] (before 2002)
Fig. 2. Age distribution for 131 OSL-dated sand samples from Giants’ church in Pattijoki Kastelli.
1290
K.O. Eskola et al. / Quaternary Science Reviews 22 (2003) 1287–1290
The sand layer from which OSL samples were collected was a coastal formation and was most likely covered with new soil after the erosion caused by the contact to the open sea ceased. Probably, the coastal sand has been affected by sunlight for a longer period and for example during stronger storms water may have washed the sand and caused erosion a long time before, as well as after the heaps were used. This would have mixed the surface of the coastal sand layer so that there can be quite long periods when sunlight has affected sand although it might never have bleached all of the sand properly. Also the erosion caused by human activity may have affected the results (especially near the heaps). There was no significant difference between the dating results of samples taken from different depths of the sand layer. This suggests that the sand was mixed effectively until the time it was covered.
Finds at the Kastelli site are from the Stone Age. From the test pit dug in the dwelling depression fragments of asbestos-tempered pottery were found. This pottery type is dated roughly to the end of the Neolithic Stone Age, approximately 2900–1800 BC. 7. Conclusions The possibility of using luminescence dating of burnt stones for a Stone Age site was tested. Quartz inclusions from the granitic stones were used for dating. Properly heated stones could be selected based on their mechanical properties and the glow curves of the quartz. The results are in good agreement with radiocarbon dates on charcoal from the site and with archaeological and shoreline displacement chronology. OSL dates of samples from the coastal sand layer, partly continuing under the heaps, shows a wide age distribution, which covers the dates from other methods.
6. Results using other than luminescence methods The site is also dated by other methods. Pieces of charcoal collected from both of the excavated heaps were radiocarbon dated. Two charcoal samples were AMS radiocarbon dated. The results are Hela-521: 4185760 BP (calibrated date 2890–2670 BC) and Hela522: 4125770 BP (calibrated date 2870–2580 BC). These results are actually telling the time when trees were growing and can thereby be 100–200 yr older than the time when the trees were burned. There are several aspects that support the idea that the heaps were used in times when the shoreline was close to the area. The studied site is situated in an area with rapid land uplift. Presently the land uplift is about 8 mm/yr. The landscape is very flat and this means that the shoreline has moved very fast due to land uplift. Shoreline displacement models from the studied area can be used to give a maximum age for the site because of this. The models are based mostly on radiocarbon results from lake sediments. This material is pointing to the period 3000–2000 BC (Nunez and Okkonen, 1999).
References B^tter-Jensen, L., Duller, G.A.T., 1992. A new system for measuring OSL from quartz samples. Nuclear Tracks and Radiation Measurements 20, 549–553. B^tter-Jensen, L., Mejdahl, V., 1988. Assessment of beta dose-rate using a GM multicounter system. Nuclear Tracks and Radiation Measuremens 14, 187–191. B^tter-Jensen, L., Mejdahl, V., Murray, A.S., 1999. New light on OSL. Quaternary Science Reviews 18, 303–309. Carpelan, C., Jungner, H., Mejdahl, V., 1992. Dating of a sub-recent Saami Winter village site near Inari, Finnish Lapland. A preliminary account. PACT 36, 9–26. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73. Nunez, M., Okkonen, J., 1999. Enviromental background for the rise and fall of villages and Megastructures in North Ostrobotnia 4000–2000 cal BC. Dig it all (Papers dedicated to Ari Siiri.ainen). The Finnish Antiquarian Society and The Archaeological Society of Finland, Helsinki, pp. 105–115. Toyoda, S., Rink W, J., Schwarcz H, P., Reese-Jones, J., 2000. Crushing effects on TL and OSL quartz: relevance to fault dating. Radiation Measurements 32, 667–672.
Luminescence dating of a coastal Stone Age dwelling place in Northern Finland K.O. Eskolaa,*, J. Okkonenb, H. Jungnera b
a Dating Laboratory, University of Helsinki, POB 64, FIN-00014 Helsinki, Finland Archaeological Laboratory, University of Oulu, POB 1000, FIN-90014 Oulu, Finland
Abstract TL and OSL methods were used in order to date an archaeologically interesting site, the Giants’ church in Kastelli, Northern Finland. The TL method was used for burnt stones collected from heaps of fire-cracked stones. At least some of the collected stones were heated properly during the times the heaps were used and that made TL dating possible. OSL measurements were made on a coastal sand layer continuing partly under the heaps. This sand layer is expected to have been formed during the same time period as the heaps were used. The results are in good agreement with radiocarbon dates on charcoal from the site and with archaeological and shoreline displacement chronology. All the results for the Kastelli site point to an age in the middle of the third millennium BC. r 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction The Giants’ church in Pattijoki Kastelli is one of the most noted archaeological sites in Northern Finland. It is located circa 60 km southwest from the town of Oulu. The site consists of several structures and archaeological features, in which the most prominent is a large rectangular stone enclosure. The size of the structure is 52 30 m2. Altogether 43 similar Giants’ church sites are known in Finland. They are all situated in the coastal area of northern Ostrobotnia. Their function is still unclear. According to isostatic land uplift and shoreline displacement chronology, they have been dated to the Stone Age. The archaeological finds found from the sites also point to the same age. The earliest studies made at the Kastelli site are from the 1860s. At 1862 one cairn was excavated, but no finds were discovered. In 1920 another excavation was made—this time the enclosure was under research. In 2001 the Finnish National Board of Antiquities arranged the survey and small-scale excavation at the Kastelli site. Mapping the site and sampling datable material was a priority. The total area of the site is approximately 3.4 ha. During the intensive surveying 43 heaps of fire-cracked stones were discovered. There are also seven dwelling depressions, most of which are the *Corresponding author.. E-mail address: kari.o.eskola@helsinki.fi (K.O. Eskola).
remains of pit houses and 19 cairns at the site. A map of the site is shown in Fig. 1. In our study we concentrated on heaps, which are most interesting for dating the site. The heaps are situated in a 150 m long band along the 52-m a.s.l. contour line. They are low mounds, which are undefined in form, and their heights range from 30 to 70 cm. The distribution marks the ancient shoreline and most likely the close access to the water was essential to the process in which the heated stones were used and the heaps were formed. The archaeological excavations clearly point to the fact that at least some of the heaps were built on the Stone Age beach. Probably, the heaps are linked to seal fat processing although the exact function of the structures is not fully understood. An earlier attempt to use heated stones from different fireplaces at Saami Winter villages in Finnish Lapland (Carpelan et al., 1992) was problematic because of relatively large difference in dating results between different fireplaces. These sites are, however, only a few hundred years old and thereby young compared to the Stone Age site at Kastelli.
2. Sampling In order to get suitable samples for dating, two of the heaps were opened (Test Pits 1 and 2 in Fig. 1). Samples of granitic stones, soil and charcoal were collected. In
0277-3791/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0277-3791(03)00077-5
1288
K.O. Eskola et al. / Quaternary Science Reviews 22 (2003) 1287–1290
The measured dose rates were relatively high. In Test Pit 1, the gamma dose rate was 1.51 mGy/a and the beta dose rate 1.89 mGy/a, giving a total dose rate of Da E3:4 mGy/a. In Test Pit 2, the gamma dose rate was 1.63 mGy/a and beta dose rate 2.19 mGy/a, giving a total dose rate of Da E3:8 mGy/a. In the coastal sand layer, the gamma dose rate was 1.33 mGy/a and beta dose rate 1.33 mGy/a, giving a total dose rate of Da E2:7 mGy/a.
4. The age of the burnt stones from the heaps
Fig. 1. Map of the Giants’ church area in Pattijoki Kastelli. The two opened heaps (Test Pits 1 and 2) are marked. The rectangular-shaped 52 30 m2 stone enclosure ‘‘the church’’ can also be seen.
addition, quartz flakes, quartz tools and some burnt animal bones (most likely of seal) were found. A clear layer (about 3–5 cm thick) of coastal sand, continuing below one of the opened heaps (Test Pit 1), was also found. Sharp-edged stones that are clearly cracked because of heating were selected for luminescence dating. Also some sand eroded from the heated stones, and thereby having the same mineralogical structure with them, was collected for beta-dose-rate measurements. Samples from the sand layer were collected from the side of the opened heap for OSL and beta-dose-rate measurements. The samples were collected carefully from different depths of the layer in order to obtain information on the time span of deposition. All samples were carefully protected from light during the collecting process. 3. Dose-rate measurements The gamma dose rate was measured at each sampling point, using a Nuclear Enterprises Ltd. PSR 8 Portable spectrometer equipped with NaI scintillation detector. Beta dose rates were measured from sand crumbled from the burned stones with a Ris^ GM-25-5 beta multicounter (B^tter-Jensen and Mejdahl, 1988). The conversion of the measured beta dose rate to absorbed dose is based on measurements on a set of samples, with known U, Th and K contents as determined by neutron activation. The conversion also includes correction for grain size and water content.
Luminescence measurements were made with an upgraded Ris^ TL-DA-12 reader (B^tter-Jensen and Duller, 1992; B^tter-Jensen et al., 1999). In total 30 stones from the heaps were collected. Half of them were from Test Pit 1 and half from Test Pit 2. The collected stones were crushed mechanically and treated with HF and HCl acid. Toyoda et al. (2000) have studied the effects of mechanical crushing on the TL signal measured from quartz samples. The results are not obvious, but in order to minimize the use of mechanical energy during the crushing operation, long etching times were preferred. From harder stones a larger scale of grain sizes were used for the same reason. Another problem was that the grains very often were polymineral containing at least quartz and feldspar. This made separation on the basis of density difficult. Also in this case longer etching times help because feldspar is removed more quickly from the grains than quartz. The purity of the separated quartz against feldspar was tested with IRSL. Some stones also contained a lot of iron. When necessary the iron was removed from samples with a magnet. The measurements were based on the regenerative dose method. Different preheat temperatures were tested and 300 C for 10 s was finally chosen. The TL signals were measured while heating the samples up to 500 C with a heating rate of 3 C/s. Background subtractions were made for each TL measurement. Natural signals were integrated over the 325 C TL peak and compared with signals from the doses given with beta source of 16.2 mGy/s after radiation times of 800, 900, 1000 and again 800 s. The difference between the first and last regenerated signal, based on the same given dose, was taken as a measure of sensitivity change. A correction assuming equal steps of sensitivity change for all heatings of the sample was applied. For a few samples the additive dose method was applied as an attempt to measure the sensitivity change between the first and second TL heating. The precision was, however, not good enough to give reliable results.
K.O. Eskola et al. / Quaternary Science Reviews 22 (2003) 1287–1290
For stones having strong dose response the sensitivity change was quite stable and the overall sensitivity change was relatively small. With some samples the shape as well as the sensitivity of the TL curve changed clearly after a couple of TL cycles was made. Results from these samples were rejected. In Table 1 absorbed doses measured for two samples each of the two opened heaps are listed. These samples have the strongest dose response and the separation between single TL results was relatively small. The errors given in Table 1, based on standard error between TL measurements made from the same sample, indicate that the equivalent dose can be measured with high precision. The main uncertainty in the age calculation stems from dose-rate determination. This uncertainty is set at around 75%. Consequently, we conclude that the stones were heated within the period 2800–2200 BC.
5. OSL results from the coastal sand The OSL measurements were made using the same Ris^ reader that was used in measurements discussed in
1289
Section 4. Quartz used for dating was density separated from the sand. The grain size used was 0.210–0.297 mm. After separation the quartz was treated with HF and HCl and used in OSL measurements based on the SAR protocol (Murray and Wintle, 2000). The absorbed dose measured from 131 single aliquot samples showed a broad distribution (see Fig. 2) with a mean value of 11.3 Gy and standard deviation 1.62 Gy. Using blindly the mean value of the natural signal would give us an age of about 4200 a. However, the distribution of the OSL measurements made from separate samples of the sand is not symmetrically Gaussian-shaped and narrow, as it should be if the sand had been completely bleached in a short time period. Instead the distribution curve is quite wide and some kind of structure can be seen. This means that there is differently bleached sand or sand bleached at different times in this sand layer. Anyhow it is possible to see that the distribution has its maximum between 4200 and 4800 yr ago. This would point to the time period 2800–2200 BC which is in good agreement with results obtained in Section 4.
Table 1 Separate TL results from two most suitable samples of burned stones from each of the opened heaps (Test Pits 1 and 2) in Kastelli site (the errors given are standard errors) Test Pit 1
Doses from separate TL measurements (Gy)
Combined doses from separate samples (Gy) Combined doses from separate Test Pits (Gy)
Test Pit 2
Sample 14
Sample 16
Sample 23
Sample 28
16.12 15.24 15.25 15.04 15.12 15.40 15.04 16.45 15.4670.19 15.3970.14
14.88 16.10 14.87 14.39 14.98 15.57 15.71 16.04 15.3270.22
15.74 14.89 17.51 15.99 19.45 17.22 18.43 17.05 17.0470.52 17.2370.27
16.73 17.91 18.11 17.51 16.99 17.26 17.44 17.50 17.4370.16
OSL results 25
Frequency
20 15 10 5 0 0
1000
2000
3000
4000
5000
6000
Age [a] (before 2002)
Fig. 2. Age distribution for 131 OSL-dated sand samples from Giants’ church in Pattijoki Kastelli.
1290
K.O. Eskola et al. / Quaternary Science Reviews 22 (2003) 1287–1290
The sand layer from which OSL samples were collected was a coastal formation and was most likely covered with new soil after the erosion caused by the contact to the open sea ceased. Probably, the coastal sand has been affected by sunlight for a longer period and for example during stronger storms water may have washed the sand and caused erosion a long time before, as well as after the heaps were used. This would have mixed the surface of the coastal sand layer so that there can be quite long periods when sunlight has affected sand although it might never have bleached all of the sand properly. Also the erosion caused by human activity may have affected the results (especially near the heaps). There was no significant difference between the dating results of samples taken from different depths of the sand layer. This suggests that the sand was mixed effectively until the time it was covered.
Finds at the Kastelli site are from the Stone Age. From the test pit dug in the dwelling depression fragments of asbestos-tempered pottery were found. This pottery type is dated roughly to the end of the Neolithic Stone Age, approximately 2900–1800 BC. 7. Conclusions The possibility of using luminescence dating of burnt stones for a Stone Age site was tested. Quartz inclusions from the granitic stones were used for dating. Properly heated stones could be selected based on their mechanical properties and the glow curves of the quartz. The results are in good agreement with radiocarbon dates on charcoal from the site and with archaeological and shoreline displacement chronology. OSL dates of samples from the coastal sand layer, partly continuing under the heaps, shows a wide age distribution, which covers the dates from other methods.
6. Results using other than luminescence methods The site is also dated by other methods. Pieces of charcoal collected from both of the excavated heaps were radiocarbon dated. Two charcoal samples were AMS radiocarbon dated. The results are Hela-521: 4185760 BP (calibrated date 2890–2670 BC) and Hela522: 4125770 BP (calibrated date 2870–2580 BC). These results are actually telling the time when trees were growing and can thereby be 100–200 yr older than the time when the trees were burned. There are several aspects that support the idea that the heaps were used in times when the shoreline was close to the area. The studied site is situated in an area with rapid land uplift. Presently the land uplift is about 8 mm/yr. The landscape is very flat and this means that the shoreline has moved very fast due to land uplift. Shoreline displacement models from the studied area can be used to give a maximum age for the site because of this. The models are based mostly on radiocarbon results from lake sediments. This material is pointing to the period 3000–2000 BC (Nunez and Okkonen, 1999).
References B^tter-Jensen, L., Duller, G.A.T., 1992. A new system for measuring OSL from quartz samples. Nuclear Tracks and Radiation Measurements 20, 549–553. B^tter-Jensen, L., Mejdahl, V., 1988. Assessment of beta dose-rate using a GM multicounter system. Nuclear Tracks and Radiation Measuremens 14, 187–191. B^tter-Jensen, L., Mejdahl, V., Murray, A.S., 1999. New light on OSL. Quaternary Science Reviews 18, 303–309. Carpelan, C., Jungner, H., Mejdahl, V., 1992. Dating of a sub-recent Saami Winter village site near Inari, Finnish Lapland. A preliminary account. PACT 36, 9–26. Murray, A.S., Wintle, A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73. Nunez, M., Okkonen, J., 1999. Enviromental background for the rise and fall of villages and Megastructures in North Ostrobotnia 4000–2000 cal BC. Dig it all (Papers dedicated to Ari Siiri.ainen). The Finnish Antiquarian Society and The Archaeological Society of Finland, Helsinki, pp. 105–115. Toyoda, S., Rink W, J., Schwarcz H, P., Reese-Jones, J., 2000. Crushing effects on TL and OSL quartz: relevance to fault dating. Radiation Measurements 32, 667–672.