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The application of 14C dating to potsherds of the Jomon period
Nuclear Instruments and Methods in Physics Research B 223–224 (2004) 716–722 www.elsevier.com/locate/nimb
The application of 14C dating to potsherds of the Jomon period Kunio Yoshida a,*, Juntaro Ohmichi b, Masanori Kinose a, Hiroko Iijima a, Ayako Oono a, Naohiro Abe a, Yumiko Miyazaki a, Hiroyuki Matsuzaki c a
The University Museum, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-0045, Japan Research Center for Nuclear Science and Technology, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan b
c
Abstract Direct dating of a potsherd itself has been investigated for one group of Jomon pottery, so-called ‘fiber-tempered pottery’, which contain a large amount of organic fiber as a temper. The best condition of alkaline treatment is examined for four samples. Each sample was divided into two parts, the surface and the black inside. A fraction of humic acid alone can be removed when a suitable moderate condition. In this study, 14 potteries have been dated. 2004 Elsevier B.V. All rights reserved. PACS: 01.90.+g Keywords: 14 C; Radiocarbon dating; Pottery; Jomon period
1. Introduction Earthenware in the Jomon period (Japanese Neolithic cultural period) was normally decorated with straw-rope patterns. The sequence of Jomon pottery has been determined on the basis of typology using forms and patterns, and by reference to stratigraphy. The time scale was determined by radiocarbon dating of accompanied samples of charcoal or shell. Recently, the AMS method enables the direct 14 C dating of potsherds themselves, using carbonized materials on the surface or inside of potsherds [1,2]. Thus far, carbonized matters on the surface originated from
*
Corresponding author. Tel./fax: +81-3-5841-8450. E-mail address: [email protected] (K. Yoshida).
food or fuel have been collected and measured. But the organic temper in the potsherd was scarcely measured because the clay materials, which constitute the pottery, contain a small amount of carbon, and they provide older ages corresponding to original clay formation. Attempts to date the potsherds themselves using the temper have been performed, but the method was not established [3–5]. In the Earliest and Early Jomon period, organic fibers were added to clay as a temper for certain purposes. The pottery containing fibers is characterized as ‘fiber-tempered pottery’. In this group, the inside color of potsherd is usually deep black, due to charred fibers which were not oxidized completely. The carbon content of the inside portion is 2–3%, and the effect of the ‘old’ carbon from clay may be ignored.
0168-583X/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2004.04.133
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
Various carbon contaminations to potsherds may have occurred in the ground, due to humic and fluvic acids and others from the surrounding soil. In this study, different chemical treatments were employed to remove completely contaminants introduced externally. In addition, a potsherd sample was cut into three parts, (1) an exterior surface, (2) an interior surface and (3) a black-colored inside portion. Those portions were treated by different ways, and were dated to evaluate the extent of contaminant removal and the influence of carbon from clay.
2. Sites and samples Admixture of fibers as temper began in the Kanto region in the middle portion of the Earliest stage of Jomon period, and its quantity increased in Nojima-type pottery in the latter portion of the period. Fibers were still added in Kurohama-type pottery in the first half of the Early stage, and after that this technology disappeared (see Fig. 3). Samples were obtained from the typical remains around Tokyo Metropolis: seven sites in three cities in Saitama Prefecture, and two sites in Kanagawa Prefecture (Fig. 1). The total number of potsherds was over 70.
717
3. Experimental 3.1. Sample preparation 3.1.1. Treatment of potsherds About 1 mm of the potsherd’s surface was shaved using a scalpel, and thrown away to remove impurities on the surface of the earthen vessel. The plant roots were completely removed using tweezers under a microscope. About 500 mg of the sample was cut off by using a diamond cutter, it was corresponding to 0.5 cm square of 1 cm thickness. The potsherd was divided into exterior and interior surface portion and the internal black portion using a micro-grinder, and these two portions were subjected to series of experiments. For routine dating, the latter was used. It was ground to a powder in agate mortar with a pestle, and weighed after drying. In order to remove contaminants during the deposition of sherds, AAA treatment (acid–alkali– acid treatment) was performed. All treatments were done in a screw capped centrifuge tube made of glass (10 ml). After centrifuging, the supernatant solution was removed by polyethylene Pasteur pipette. First, 1 M HCl was added to the sample, and heated at 80 C for 6–12 h to remove carbonates
Fig. 1. Locations of archeological sites.
718
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
and fulvic acid contaminants. The supernatant was removed and washed with Millipore water for several times (first acid treatment). A sodium hydroxide solution (0.01 M) was added to remove humic acid contaminants. The concentration of the solution was appropriate for the condition of the sample. A solution was heated for the suitable time until it became dark brown, and it was used for dating as ‘humic acid fraction’ sample. A solution was removed and washed with Millipore water. After that, NaOH solution was added again, and heated for the suitable time. The concentration of the NaOH solution was increased gradually. It is a principle to repeat this operation until the solution stops coloring, but in the case of potsherds, alkaline concentration and heating time were adjusted according to the condition of the sample (alkaline treatment). After that it was washed with Millipore water, 1 M HCl was added and heated at 80 C for about 2 h (second acid
treatment). It was washed with Millipore water until it got rid of hydrochloric acid completely at the end. The sample was heated at 80 C and dried in the centrifuge tube. In this study, for the purpose of checking dates based on the difference in the procedure of a chemical treatment, several samples, not treated by alkaline solution or treated with different concentrations of alkaline solution, were prepared from the same potsherd for dating. 3.1.2. Humic acid fraction For precipitation of humic acid, concentrated HCl was added to the dark brown solution obtained in the process of alkaline treatment for the inside portion. A precipitate was dissolved with 0.5 M NaOH again, and the supernatant solution was pipetted off after centrifuging to remove impurities such as sand. Then 6 M HCl was added to the solution and heated at 90 C for 4 h and humic
Table 1 Effect of alkaline treatment on potsherd ages Site (type of pottery)
Sherd portion
Concentration of NaOH (M)
The residue after AAA treatment (%)
Carbon content (%)
14
C age BP ± 1r
d 13 CPDB (&)
Lab code TKa No.
Shukushimo (Kurohama-1)
Inside
1.2 0.01–0.05 Not-treated 0.01–0.04 Not-treated –
50.9 47.0 78.7 61.0 77.4 –
1.32 1.05 2.46 0.21 0.47 –
5790 ± 90 5890 ± 150 5510 ± 80 5640 ± 80 4660 ± 90 5470 ± 260
)25.54 )25.59 )25.74 – – –
11933 11931 11932 11929 11930 11945
1.2 0.5 0.05 Not-treated 0.01–0.15 Not-treated
48.3 47.7 55.4 67.9 56.2 71.6
0.60 0.46 0.87 1.54 0.34 1.12
6340 ± 100 6380 ± 80 6220 ± 130 5910 ± 80 6140 ± 90 5660 ± 80
– – – )24.48 – )23.34
11992 11993 11991 11990 11989 11988
1.2 0.01–0.06 Not-treated 0.01–0.06 Not-treated
40.0 41.5 75.8 44.2 69.2
1.59 1.76 2.16 0.27 2.25
6160 ± 210 6160 ± 100 5960 ± 160 6190 ± 130 6230 ± 100
)25.00 – )24.7 – –
11938 11936 11937 11934 11935
1.2 0.01–1.2 Not-treated 0.01–1.2 Not-treated
56.2 62.0 74.5 40.1 78.9
0.77 1.43 2.39 0.17 0.79
6280 ± 100 6010 ± 70 5570 ± 70 7000 ± 70 5790 ± 150
)24.6 )24.5 )24.3 – )24.1
11928 11926 11927 11925 11924
Surface Humic acid Yoshioka (Kurohama)
inside
Surface Sakadou shell midden (Hanazumikaso-new)
Inside
Surface Takinomiyasaka (Hanazumikaso-old)
Inside
Surface
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
Kurohama-1
2.5% 0.2% 0.5%
1.2M NaOH 0.5M NaOH 0.05M NaOH
Yoshioka
1.3% 1.1%
1.2M NaOH
inside;AAA inside;Acid only surface;AAA surface;Acid only humic acid
Shukushimo
719
0.6% 0.5% 0.9%
Kurohama
1.5% 0.3% 1.1% 1.6% 1.8%
1.2M NaOH
Sakadou shell midden
2.2% 0.3% 2.3%
Hanazumikaso-new 1.2M NaOH
Takinomiyasaka
0.8% 1.4% 2.4%
Hanazumikaso-old
0.2% 0.8%
7500
7000
6500
6000
5500
5000
4500
BP Fig. 2. Results of 14 C dating using different chemical treatments on the surface and the inside portions of potsherds. The values written on the right hand represent carbon content of the sample. Table 2 Radiocarbon ages of fiber-tempered pottery sherds Type of pottery
Site
Location
Species of sample (except potsherd)
The residue after AAA treatment (%)
Carbon content (%)
14 C age BP ± 1r
d 13 CPDB (&)
Lab code TKa No.
Kurohama
Shukushimo
8 8 20 44 5 3 K3
Shell
– 50.7 – 69.6 41.2 58.9 65.5
– 0.81 – 2.76 1.26 1.08 1.30
5660 ± 80 5380 ± 90 5940 ± 130 5660 ± 90 5780 ± 120 5970 ± 90 9860 ± 210
)4.40 – )3.62 )25.59 )24.97 )24.90 )25.79
11949 11638 11898 11885 11942 11888 11887
4
Shell
–
–
6164 ± 110
)3.58
11947
4 153
46.7 56.6
1.56 1.93
5870 ± 110 6010 ± 90
)25.11 )25.36
11997 11884
246 1
67.9 54.1
2.92 1.71
6060 ± 90 6170 ± 90
)25.06 )24.79
11945 11886
080 483 222 328 Kl
53.2 68.2 65.6 75.3 67.2
0.65 2.27 2.32 1.04 1.39
6420 ± 90 6420 ± 100 6630 ± 150 6710 ± 90 7210 ± 90
)25.51 – )25.31 )25.12 )25.75
11883 11944 11890 11941 11946
1034 328
56.2 55.0
1.70 1.69
7620 ± 120 7710 ± 80
)26.02 )21.60
11882 11943
Yoshioka Shukugami Sekiyama
Sekiyama shell midden Tosakimae
Hanazumikaso
Shimonodan Sakadou shell midden Takinomiyasaka
Shukugami Nojima
Ichibeidani
Shell
720
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
acid was reprecipitated. The precipitate was washed with Millipore water until it reached at about pH 3 at the end. It was then heated at 80 C for drying. All operations were done in a screw capped centrifuge tube. 3.2. Oxidation and graphitization The sample containing about 1–2 mg of carbon was mixed with 1 g of CuO wire and transferred to
a Vycor tube. The tube was adapted to a vacuum manifold after adding 3 pieces of Ag foil (3 cm · 4 mm, 0.03 mm thickness) and evacuated. The tube was then torch sealed and heated in a furnace at 500 C for 30 min and at 850 C for 2 h. The converted CO2 gas was purified cryogenically. The process of reduction to graphite is the same manner described in [6]. The 13 C/12 C ratio of the CO2 gas was measured using a Finnigan MAT 252 gas ion-source mass spectrometer at the
Fig. 3. Calibrated ages of fiber-tempered pottery sherds.
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
Department of Earth and Planetary Science, Faculty of Science, the University of Tokyo. 3.3.
14
C age measurement by AMS
Radiocarbon dates were measured by our standardized method using a tandem accelerator mass spectrometer at MALT, the University of Tokyo [7].
4. Results and discussion Samples for comparison were selected as follows, (1) a large fragment, (2) a deep black inside portion and (3) a comparatively thick surface. Radiocarbon dates corresponding to the different chemical treatments are shown in Table 1 and Fig. 2. Carbon content: The inside part content (1.5– 2.5%) is bigger than the surface one (0.5–2.3%) as it was expected (as for Sakadou sample, both are about the same). Humic acid: Dates generally become older after alkaline treatment except Sakadou sample, and it can be presumed that humic acid of the upper layer permeated to the lower one. Actually, the humic acid fraction collected from the alkaline solution shows a younger age, although the error is large because of the small sample size. The age agreed very closely with the value of the internal black portion treated only by acid. It shows that most of contaminants are humic acid components, and can be removed by alkaline treatment. Elution by strong alkaline solutions seems not so serious. The influence of ‘old’ carbon in clay: The surface part of Takinomiyasaka sample is a good example, wherein ‘old’ carbon from clay excels when carbon content decreases to 1/4 of the original value (0.17% versus 0.79%). Therefore, sherds of the usual ‘fiber-tempered pottery’ are treated with about 0.05 M NaOH, and as a result: (1) humic acid contaminations are removed, (2) carbon from the fiber is left in the place and the influence of ‘old’ carbon from the clay can be ignored and (3) reasonable dates of potsherds can be obtained. First of all, 16 samples were treated by the above-mentioned optimal way, and their age was measured together with three shell
721
samples (Table 2). The 14 C ages were calibrated using the OxCal 3.5 program [8] with INTCAL98 calibration data [9], and compared with the literature values. When there are many carefully selected values for the pottery type [10], the oldest and the youngest one are shown in Fig. 3. Two sets of shell and potsherd samples inside the dashed line frame are associated with each other, and their dates show good agreement. The 14 C ages of shell samples were calibrated with MARINE98 calibration data. The relation as a whole is consistent with each other. Nevertheless, two potsherds excavated from the Shukugami site were both shown to be considerably older than other dates (* in Table 2). They are eliminated from Fig. 3, and the cause of the older dates is under investigation. 5. Conclusions Potsherds of ‘fiber earthenware’ themselves can be dated using the black-colored inside portion and 14 radiocarbon dates were obtained. Acknowledgements We acknowledge Dr. K. Kobayashi, Dr. Y. Maejima and Mr. C. Nakano for their help on AMS measurements. We would like to appreciate Mr. S. Oda and T. Ushino for collecting samples and fruitful discussion. This work was supported partly by the ‘Grant-In-Aid for Scientific Research’ of the Japan Society for the Promotion of Science (subject nos. 08451086, 11301013, and 14201042). References [1] K. Yoshida, A. Honda, Abstracts of the 14th meeting of Jap. Soc. for Scientific Studies on Cultural Property, 1997, 24 (in Japanese). [2] T. Nakamura, Y. Taniguchi, S. Tsuji, H. Oda, Radiocarbon 43 (2001) 1129. [3] J.M. O’Malley, Y.V. Kuzmin, G.S. Burr, D.J. Donahue, A.J.T. Jull, Actes Coll. C14 Archeol. 19 (1998). [4] M. Gabasio, J. Evin, G.B. Arnal, P. Andrieux, Radiocarbon 28 (1986) 711. [5] R.E.M. Hedges, T. Chen, R.A. Housley, Radiocarbon 34 (1992) 906.
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K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
[6] Y. Miyairi, K. Yoshida, Y. Miyazaki, H. Matsuzaki, I. Kaneoka, Nucl. Instr. and Meth. B, these Proceedings. doi:10.1016/j.nimb.2004.04.103. [7] J. Ohmichi, K. Yoshida, M. Kinose, S. Hishiki, T. Tanaka, Y. Miyazaki, H. Matsuzaki, H. Nagai, Nucl. Instr. and Meth. B, 2003.
[8] C.B. Ramsey, OxCal v. 3.5, 2000. [9] M. Stuiver, P.J. Reimer, E. Bard, J.W. Beck, G.S. Burr, K.A. Hughen, B. Kromer, F.G. McCormac, J. van der Plicht, M. Spurk, Radiocarbon 40 (1998) 1041. [10] Y. Taniguchi, Archaeol. Quart. No. 77, 2001, 17 (in Japanese).
The application of 14C dating to potsherds of the Jomon period Kunio Yoshida a,*, Juntaro Ohmichi b, Masanori Kinose a, Hiroko Iijima a, Ayako Oono a, Naohiro Abe a, Yumiko Miyazaki a, Hiroyuki Matsuzaki c a
The University Museum, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-0033, Japan College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajosui, Setagaya-ku, Tokyo 156-0045, Japan Research Center for Nuclear Science and Technology, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan b
c
Abstract Direct dating of a potsherd itself has been investigated for one group of Jomon pottery, so-called ‘fiber-tempered pottery’, which contain a large amount of organic fiber as a temper. The best condition of alkaline treatment is examined for four samples. Each sample was divided into two parts, the surface and the black inside. A fraction of humic acid alone can be removed when a suitable moderate condition. In this study, 14 potteries have been dated. 2004 Elsevier B.V. All rights reserved. PACS: 01.90.+g Keywords: 14 C; Radiocarbon dating; Pottery; Jomon period
1. Introduction Earthenware in the Jomon period (Japanese Neolithic cultural period) was normally decorated with straw-rope patterns. The sequence of Jomon pottery has been determined on the basis of typology using forms and patterns, and by reference to stratigraphy. The time scale was determined by radiocarbon dating of accompanied samples of charcoal or shell. Recently, the AMS method enables the direct 14 C dating of potsherds themselves, using carbonized materials on the surface or inside of potsherds [1,2]. Thus far, carbonized matters on the surface originated from
*
Corresponding author. Tel./fax: +81-3-5841-8450. E-mail address: [email protected] (K. Yoshida).
food or fuel have been collected and measured. But the organic temper in the potsherd was scarcely measured because the clay materials, which constitute the pottery, contain a small amount of carbon, and they provide older ages corresponding to original clay formation. Attempts to date the potsherds themselves using the temper have been performed, but the method was not established [3–5]. In the Earliest and Early Jomon period, organic fibers were added to clay as a temper for certain purposes. The pottery containing fibers is characterized as ‘fiber-tempered pottery’. In this group, the inside color of potsherd is usually deep black, due to charred fibers which were not oxidized completely. The carbon content of the inside portion is 2–3%, and the effect of the ‘old’ carbon from clay may be ignored.
0168-583X/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2004.04.133
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
Various carbon contaminations to potsherds may have occurred in the ground, due to humic and fluvic acids and others from the surrounding soil. In this study, different chemical treatments were employed to remove completely contaminants introduced externally. In addition, a potsherd sample was cut into three parts, (1) an exterior surface, (2) an interior surface and (3) a black-colored inside portion. Those portions were treated by different ways, and were dated to evaluate the extent of contaminant removal and the influence of carbon from clay.
2. Sites and samples Admixture of fibers as temper began in the Kanto region in the middle portion of the Earliest stage of Jomon period, and its quantity increased in Nojima-type pottery in the latter portion of the period. Fibers were still added in Kurohama-type pottery in the first half of the Early stage, and after that this technology disappeared (see Fig. 3). Samples were obtained from the typical remains around Tokyo Metropolis: seven sites in three cities in Saitama Prefecture, and two sites in Kanagawa Prefecture (Fig. 1). The total number of potsherds was over 70.
717
3. Experimental 3.1. Sample preparation 3.1.1. Treatment of potsherds About 1 mm of the potsherd’s surface was shaved using a scalpel, and thrown away to remove impurities on the surface of the earthen vessel. The plant roots were completely removed using tweezers under a microscope. About 500 mg of the sample was cut off by using a diamond cutter, it was corresponding to 0.5 cm square of 1 cm thickness. The potsherd was divided into exterior and interior surface portion and the internal black portion using a micro-grinder, and these two portions were subjected to series of experiments. For routine dating, the latter was used. It was ground to a powder in agate mortar with a pestle, and weighed after drying. In order to remove contaminants during the deposition of sherds, AAA treatment (acid–alkali– acid treatment) was performed. All treatments were done in a screw capped centrifuge tube made of glass (10 ml). After centrifuging, the supernatant solution was removed by polyethylene Pasteur pipette. First, 1 M HCl was added to the sample, and heated at 80 C for 6–12 h to remove carbonates
Fig. 1. Locations of archeological sites.
718
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
and fulvic acid contaminants. The supernatant was removed and washed with Millipore water for several times (first acid treatment). A sodium hydroxide solution (0.01 M) was added to remove humic acid contaminants. The concentration of the solution was appropriate for the condition of the sample. A solution was heated for the suitable time until it became dark brown, and it was used for dating as ‘humic acid fraction’ sample. A solution was removed and washed with Millipore water. After that, NaOH solution was added again, and heated for the suitable time. The concentration of the NaOH solution was increased gradually. It is a principle to repeat this operation until the solution stops coloring, but in the case of potsherds, alkaline concentration and heating time were adjusted according to the condition of the sample (alkaline treatment). After that it was washed with Millipore water, 1 M HCl was added and heated at 80 C for about 2 h (second acid
treatment). It was washed with Millipore water until it got rid of hydrochloric acid completely at the end. The sample was heated at 80 C and dried in the centrifuge tube. In this study, for the purpose of checking dates based on the difference in the procedure of a chemical treatment, several samples, not treated by alkaline solution or treated with different concentrations of alkaline solution, were prepared from the same potsherd for dating. 3.1.2. Humic acid fraction For precipitation of humic acid, concentrated HCl was added to the dark brown solution obtained in the process of alkaline treatment for the inside portion. A precipitate was dissolved with 0.5 M NaOH again, and the supernatant solution was pipetted off after centrifuging to remove impurities such as sand. Then 6 M HCl was added to the solution and heated at 90 C for 4 h and humic
Table 1 Effect of alkaline treatment on potsherd ages Site (type of pottery)
Sherd portion
Concentration of NaOH (M)
The residue after AAA treatment (%)
Carbon content (%)
14
C age BP ± 1r
d 13 CPDB (&)
Lab code TKa No.
Shukushimo (Kurohama-1)
Inside
1.2 0.01–0.05 Not-treated 0.01–0.04 Not-treated –
50.9 47.0 78.7 61.0 77.4 –
1.32 1.05 2.46 0.21 0.47 –
5790 ± 90 5890 ± 150 5510 ± 80 5640 ± 80 4660 ± 90 5470 ± 260
)25.54 )25.59 )25.74 – – –
11933 11931 11932 11929 11930 11945
1.2 0.5 0.05 Not-treated 0.01–0.15 Not-treated
48.3 47.7 55.4 67.9 56.2 71.6
0.60 0.46 0.87 1.54 0.34 1.12
6340 ± 100 6380 ± 80 6220 ± 130 5910 ± 80 6140 ± 90 5660 ± 80
– – – )24.48 – )23.34
11992 11993 11991 11990 11989 11988
1.2 0.01–0.06 Not-treated 0.01–0.06 Not-treated
40.0 41.5 75.8 44.2 69.2
1.59 1.76 2.16 0.27 2.25
6160 ± 210 6160 ± 100 5960 ± 160 6190 ± 130 6230 ± 100
)25.00 – )24.7 – –
11938 11936 11937 11934 11935
1.2 0.01–1.2 Not-treated 0.01–1.2 Not-treated
56.2 62.0 74.5 40.1 78.9
0.77 1.43 2.39 0.17 0.79
6280 ± 100 6010 ± 70 5570 ± 70 7000 ± 70 5790 ± 150
)24.6 )24.5 )24.3 – )24.1
11928 11926 11927 11925 11924
Surface Humic acid Yoshioka (Kurohama)
inside
Surface Sakadou shell midden (Hanazumikaso-new)
Inside
Surface Takinomiyasaka (Hanazumikaso-old)
Inside
Surface
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
Kurohama-1
2.5% 0.2% 0.5%
1.2M NaOH 0.5M NaOH 0.05M NaOH
Yoshioka
1.3% 1.1%
1.2M NaOH
inside;AAA inside;Acid only surface;AAA surface;Acid only humic acid
Shukushimo
719
0.6% 0.5% 0.9%
Kurohama
1.5% 0.3% 1.1% 1.6% 1.8%
1.2M NaOH
Sakadou shell midden
2.2% 0.3% 2.3%
Hanazumikaso-new 1.2M NaOH
Takinomiyasaka
0.8% 1.4% 2.4%
Hanazumikaso-old
0.2% 0.8%
7500
7000
6500
6000
5500
5000
4500
BP Fig. 2. Results of 14 C dating using different chemical treatments on the surface and the inside portions of potsherds. The values written on the right hand represent carbon content of the sample. Table 2 Radiocarbon ages of fiber-tempered pottery sherds Type of pottery
Site
Location
Species of sample (except potsherd)
The residue after AAA treatment (%)
Carbon content (%)
14 C age BP ± 1r
d 13 CPDB (&)
Lab code TKa No.
Kurohama
Shukushimo
8 8 20 44 5 3 K3
Shell
– 50.7 – 69.6 41.2 58.9 65.5
– 0.81 – 2.76 1.26 1.08 1.30
5660 ± 80 5380 ± 90 5940 ± 130 5660 ± 90 5780 ± 120 5970 ± 90 9860 ± 210
)4.40 – )3.62 )25.59 )24.97 )24.90 )25.79
11949 11638 11898 11885 11942 11888 11887
4
Shell
–
–
6164 ± 110
)3.58
11947
4 153
46.7 56.6
1.56 1.93
5870 ± 110 6010 ± 90
)25.11 )25.36
11997 11884
246 1
67.9 54.1
2.92 1.71
6060 ± 90 6170 ± 90
)25.06 )24.79
11945 11886
080 483 222 328 Kl
53.2 68.2 65.6 75.3 67.2
0.65 2.27 2.32 1.04 1.39
6420 ± 90 6420 ± 100 6630 ± 150 6710 ± 90 7210 ± 90
)25.51 – )25.31 )25.12 )25.75
11883 11944 11890 11941 11946
1034 328
56.2 55.0
1.70 1.69
7620 ± 120 7710 ± 80
)26.02 )21.60
11882 11943
Yoshioka Shukugami Sekiyama
Sekiyama shell midden Tosakimae
Hanazumikaso
Shimonodan Sakadou shell midden Takinomiyasaka
Shukugami Nojima
Ichibeidani
Shell
720
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
acid was reprecipitated. The precipitate was washed with Millipore water until it reached at about pH 3 at the end. It was then heated at 80 C for drying. All operations were done in a screw capped centrifuge tube. 3.2. Oxidation and graphitization The sample containing about 1–2 mg of carbon was mixed with 1 g of CuO wire and transferred to
a Vycor tube. The tube was adapted to a vacuum manifold after adding 3 pieces of Ag foil (3 cm · 4 mm, 0.03 mm thickness) and evacuated. The tube was then torch sealed and heated in a furnace at 500 C for 30 min and at 850 C for 2 h. The converted CO2 gas was purified cryogenically. The process of reduction to graphite is the same manner described in [6]. The 13 C/12 C ratio of the CO2 gas was measured using a Finnigan MAT 252 gas ion-source mass spectrometer at the
Fig. 3. Calibrated ages of fiber-tempered pottery sherds.
K. Yoshida et al. / Nucl. Instr. and Meth. in Phys. Res. B 223–224 (2004) 716–722
Department of Earth and Planetary Science, Faculty of Science, the University of Tokyo. 3.3.
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C age measurement by AMS
Radiocarbon dates were measured by our standardized method using a tandem accelerator mass spectrometer at MALT, the University of Tokyo [7].
4. Results and discussion Samples for comparison were selected as follows, (1) a large fragment, (2) a deep black inside portion and (3) a comparatively thick surface. Radiocarbon dates corresponding to the different chemical treatments are shown in Table 1 and Fig. 2. Carbon content: The inside part content (1.5– 2.5%) is bigger than the surface one (0.5–2.3%) as it was expected (as for Sakadou sample, both are about the same). Humic acid: Dates generally become older after alkaline treatment except Sakadou sample, and it can be presumed that humic acid of the upper layer permeated to the lower one. Actually, the humic acid fraction collected from the alkaline solution shows a younger age, although the error is large because of the small sample size. The age agreed very closely with the value of the internal black portion treated only by acid. It shows that most of contaminants are humic acid components, and can be removed by alkaline treatment. Elution by strong alkaline solutions seems not so serious. The influence of ‘old’ carbon in clay: The surface part of Takinomiyasaka sample is a good example, wherein ‘old’ carbon from clay excels when carbon content decreases to 1/4 of the original value (0.17% versus 0.79%). Therefore, sherds of the usual ‘fiber-tempered pottery’ are treated with about 0.05 M NaOH, and as a result: (1) humic acid contaminations are removed, (2) carbon from the fiber is left in the place and the influence of ‘old’ carbon from the clay can be ignored and (3) reasonable dates of potsherds can be obtained. First of all, 16 samples were treated by the above-mentioned optimal way, and their age was measured together with three shell
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samples (Table 2). The 14 C ages were calibrated using the OxCal 3.5 program [8] with INTCAL98 calibration data [9], and compared with the literature values. When there are many carefully selected values for the pottery type [10], the oldest and the youngest one are shown in Fig. 3. Two sets of shell and potsherd samples inside the dashed line frame are associated with each other, and their dates show good agreement. The 14 C ages of shell samples were calibrated with MARINE98 calibration data. The relation as a whole is consistent with each other. Nevertheless, two potsherds excavated from the Shukugami site were both shown to be considerably older than other dates (* in Table 2). They are eliminated from Fig. 3, and the cause of the older dates is under investigation. 5. Conclusions Potsherds of ‘fiber earthenware’ themselves can be dated using the black-colored inside portion and 14 radiocarbon dates were obtained. Acknowledgements We acknowledge Dr. K. Kobayashi, Dr. Y. Maejima and Mr. C. Nakano for their help on AMS measurements. We would like to appreciate Mr. S. Oda and T. Ushino for collecting samples and fruitful discussion. This work was supported partly by the ‘Grant-In-Aid for Scientific Research’ of the Japan Society for the Promotion of Science (subject nos. 08451086, 11301013, and 14201042). References [1] K. Yoshida, A. Honda, Abstracts of the 14th meeting of Jap. Soc. for Scientific Studies on Cultural Property, 1997, 24 (in Japanese). [2] T. Nakamura, Y. Taniguchi, S. Tsuji, H. Oda, Radiocarbon 43 (2001) 1129. [3] J.M. O’Malley, Y.V. Kuzmin, G.S. Burr, D.J. Donahue, A.J.T. Jull, Actes Coll. C14 Archeol. 19 (1998). [4] M. Gabasio, J. Evin, G.B. Arnal, P. Andrieux, Radiocarbon 28 (1986) 711. [5] R.E.M. Hedges, T. Chen, R.A. Housley, Radiocarbon 34 (1992) 906.
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[6] Y. Miyairi, K. Yoshida, Y. Miyazaki, H. Matsuzaki, I. Kaneoka, Nucl. Instr. and Meth. B, these Proceedings. doi:10.1016/j.nimb.2004.04.103. [7] J. Ohmichi, K. Yoshida, M. Kinose, S. Hishiki, T. Tanaka, Y. Miyazaki, H. Matsuzaki, H. Nagai, Nucl. Instr. and Meth. B, 2003.
[8] C.B. Ramsey, OxCal v. 3.5, 2000. [9] M. Stuiver, P.J. Reimer, E. Bard, J.W. Beck, G.S. Burr, K.A. Hughen, B. Kromer, F.G. McCormac, J. van der Plicht, M. Spurk, Radiocarbon 40 (1998) 1041. [10] Y. Taniguchi, Archaeol. Quart. No. 77, 2001, 17 (in Japanese).