地球環境研究，Vol.19（2017）

Geomorphological development at Paleolithic
sites of Imjin River Region, Korea, inferredfrom luminescence dating
SHITAOKA Yorinao ＊YAGI Hiroshi ＊＊＊NAGATOMO Tsuneto ＊＊YI Seonbok ＊＊＊＊

キーワード：Paleolithic sites, Imjin River, Geomorphological development, Basalt lava,
Luminescence dating, Korea

1. Introduction
Paleolithic sites along the Imjin and Hantan rivers in

Ma（see Table 1）. Recently, four FT ages around 0.40
Ma were obtained from baked gravel lying below thelava at Chongokri and Baekuiri（Yi et al., 2005）.

Korea were investigated following the discovery of a

In relation to the timing of the basalt flow, previous

hand axe at Chongokri village by a U.S. soldier in 1978

studies have tended to regard basalt flow as occurring（Cultural relics in Seoul National University Museum,

during a single geological event. However, a review of1997）. Artifacts found at Paleolithic sites of Wongdan-

data available from earlier studies （Table 1） reveals

gri, Kawoli, Juwoli, Kumpari, and other locations are

three clusters of dates for the basalt lavas（younger

regarded as resembling those found at the Chongokri

than 200 ka, ca. 280 ka, and older than 400 ka）, imply-

site, which include Acheulean-like bifaces. However,ing the possibility of intermittent inflows of the basalt

none has been dated scientifically because the artifact

lavas that filled the valleys during the middle Pleisto-

horizons lack suitable materials for dating. Most sites

cene. Nevertheless, no stratigraphic or geomorphologi-

are distributed on a depositional surface of basalt lavas

cal evidence indicates that there indeed did occur threethat moved rapidly along the Hantan River fromor more episodes of volcanic eruptions and subsequent

Pyounggang as a source vent, burying the valleys of thelava flows（Yi et al., 2005; Yi et al., 2006）.

Imjin and Hantan rivers. Therefore, to date, the esti-

An upper age limit for the Paleolithic sites in themated ages of the Paleolithic sites reported in thisstudy area is inferred as ca. 30 ka, based on the volca-

study area have been based on dating of the basalt lava

nic glasses of Aira-Tn tephra（AT）, which overlie theflows.

occupation levels at Chongokri and Kawoli sites （Yi,The age of the Chongokri basalt, 0.108±0.158 Ma,

1998）.Soil wedges in surface deposits of the basalt lava

was obtained first by application of the potassium-provide another potential indicator of age based on

argon（K-Ar）method（Takayanagi, 1983）. Thereafter,

association with the climatic stage（Bae et al., 2001）,

other dating methods including fission track （FT）,

but the formation of a soil wedge is not necessarily evi-

paleomagnetism（PM）, electron spin resonance（ESR）,

dence of a cold stage because it has been observed inthermoluminescence （TL）, and optically stimulated

Holocene contexts（Yi, 1998）.

luminescence（OSL）, in addition to further K-Ar dating,In the absence of dating of the artifact horizons athave been applied to the basalt and the deposits. How-

these sites, OSL dating（first proposed by Huntley etever, K-Ar ages for the basalts range widely: 0.108 -al., 1985）was applied to samples that had been exposed

sufficiently to sunlight before deposition. Aeolian depos0.85 Ma. The FT ages for the deposits are 0.11 - 0.51
＊			 Rissho University＊＊
		 Emeritus Professor, Nara University of Education＊＊＊
		 Yamagata University＊＊＊＊
Seoul National University, Korea

29

Geomorphological development at Paleolithic sites of Imjin River Region, Korea, inferred from luminescence dating（Shitaoka et al.）Table 1< 200 ka

〜280 ka> 400 ka -Ar and FT ages obtained for the basalt lava along the Imjin RiverK
and Hantan River, Korea. These ages are clustered into threegroups: < 200 ka, ca. 280 ka, and > 400 ka.

Locality, sample

MethodAge (Ma)

Chongokri, basalt

K-Ar

0.108±0.158

Eundaeri（Pung cheonfarm）, basalt

K-Ar

basaltFTbasaltK-Ar

0.14–0.18

Cholwon, basalt（top1）
Cholwon, basalt（top2）
Sangsari, basalt

K-Ar
K-Ar
K-Ar

0.28±0.07
0.28±0.07
0.28±0.07

Cholwon, basalt 2nd（L. from Bottom）

K-Ar

0.69±0.06

Lee et al ., 1983

0.16±0.05
0.18±0.02
0.13±0.02
0.11±0.03

Nagaoka et al .,2008

Chatan Basalt

Lee et al ., 1983
Lee, 1992*

0.6±0.2

Yi, 1983*

K-Ar
K-Ar

Eundaeri（Changjinchon）, basalt

K-Ar

0.6231±0.018
0.49±0.05
0.85±0.03
0.50±0.03
0.57±0.03

Deino, 1988*

Chongokni, basalt

Chongokri, Baekuiri, silt

FTbasaltK-Ar

0.49–0.55,

plagioclase
Whole-rockBelow Chatan Basalt

K-Ar

0.51±0.07

Notes

Nagaoka et al .,2008

Chongokni, Lower,
bottomChongokni, basalt

0.51±0.07＊

Reference
Takayanagi,
1983
Danhara et al .,2002

Danhara et al .,2002

plagioclase
Whole-rockplagioclase
Whole-rock
0-2 cm below basalt /basement boundary

Danhara et al .,2002
10-15 m below basalt /basement boundary
Nagaoka et al .,2008

Chongok basalt

in the fourth column is quoted from a reference by Bae（2002）.

its are the optimum sample for OSL methods, but gen-northeast of Seoul. The Imjin River flows from North

erally speaking, sediments that have been deposited

Korea and joins the Hantan River at Tongiri, 3 km west

slowly with episodes of daylight exposure are poten-of Chongokri. Then it flows westward into the Yellow

tially suitable. Measurements using TL method wereSea （Fig. 1）. Topographic variation exists along theattempted with soil samples in the study area in 1984,

Imjin-Hantan valley. The area’s Quaternary geology and

1993, and 1994（Yi, 1998）, but it is noteworthy that theygeomorphology were clarified by Yi（1988）. The valley

were studied preliminarily because the dose rates used

is filled with thick basalt lava overlying the Baekuiri

to calculate the luminescence age were based on esti-

Formation, with buried terrace deposits that are identi-

mated data.

fiable along the present river course of the Hantan

In this study, measurements using both OSL and TL

River in the vicinity of Chongokri. The depositional sur-methods were taken of samples of sediments from theface of the basalt lava resembles that of a river terrace.

archeological sites and of pebbles and soil heated byWith slight erosion it has formed a lava strath terrace.

basalt lavas filling the valley of the Imjin and Hantan

A lower fluvial terrace has also developed along therivers. The geomorphological development of thisfoot of the basalt terrace（Fig. 2）. Both the basalt lava

region was assessed based on the obtained lumines-

and the subsequent lava strath terraces are traceable

cence ages.

from Chongokri to Kawoli, Juwoli and Kumpari. The
Paleolithic artifacts found at Chongokri were excavated

2. Sample locations
Chongokri lies along the Hantan River, located 50 km
30from the horizons of the flood or aeolian sediments
overlying the basalt lava. The basalt lava did not reachJangsanri, and a higher fluvial terrace occurs sporadi-地球環境研究，Vol.19（2017）

Fig. 1

 opographical map and the Paleolithic sites and outcrops along the Imjin
TRiver and Hantan River, where samples were collected for this study.

Fig. 2

Table 2
Site
Jangsanri
Chongokri

Geological cross section of the Hantan
Valley near Chongokri.（Bae, 2002）

Locations and descriptions of the samples used for this study.

Sample locations and context descriptions
Three horizons below the artifact horizon where hand axes, choppers and cores were found (Yi, 1998).
The upper layers of the terrace are composed of clay containing some pebbles. The lower layers contain manylarge pebbles.
Loamy materials (N8E16 grid) surveyed by Yi (2004) sampled from, within and above the artifact forizon,
respectively.
Three depositional samples collected above the artifact horizon at the E55S20-IV grid surveyed by Bae (2001).

Kawoli

Loamy materials above and below the artifact horizon at Loc 2 (TP19 grid) and Loc 3, respectively.

Kumpari

Loamy materials within the artifact horizon and underlying clay in W80S390 grid.

Outcrop

Sample locations and context descriptions

Baekuiri

Reddish granite gravels beneath the basalt lava.
38º 1' 7.7"N, 127º 8' 26.9"E
Buried soil beneath basalt lava.
38º 0' 8.9"N, 127º 0' 28.3"E

Tongiri31

Geomorphological development at Paleolithic sites of Imjin River Region, Korea, inferred from luminescence dating（Shitaoka et al.）cally in the lower course of Jangsanri along the Imjin

for ca. 16 hr. Samples were separated into two portions

River. The terrace formed before the inflow of theby suspension in acetone: 4-10 µm （polymineral finebasalt lava into the valley and developed at a higher

grains） and 10-50 µm （polymineral semi-fine grains）

level than that of the basalt lava. Paleolithic artifacts（Zimmerman, 1977）. The fine and semi-fine grain frac-were also excavated from the higher terrace at Jang-

tions were treated with 20% hydrochloric acid（HCl）

sanri.

for 2 hr to remove carbonate minerals such as calcite

The locations of samples tested using luminescencemethods are presented in Table 2.

and aragonite. The distribution of grain size of semi-finegrains was measured using a digital microscope（VHX100; Keyence Co.）. The estimated size range of the

3. Measurements
3.1 Equipment

semi-fine grains was 15-30 µm. Grains larger than 50µm were not observed.
For BLSL measurements with quartz fine grains,

For this study, OSL measurements were made withminerals treated with HCl were treated for 9 days

a TL/OSL reader, NRL-99-OSTL, designed and con-more with hydrosilicofluoric acid （ H 2 [SiF 6 ]）. Thestructed by Nagatomo et al.（2005）. Infrared stimulated

obtained sample was examined using X-ray diffraction

luminescence（IRSL）and blue-light stimulated lumines-

analysis, but no peak other than that of quartz wascence（BLSL）were stimulated respectively using LED

observed. Furthermore, the purity of quartz extracts

assemblies with 32 LEDs, 890±50 nm for IRSL and 470

was verified using IRSL. If feldspar remained, then

±40 nm for BLSL. Luminescence from samples was

H2 [SiF6] treatment was repeated.

detected with a photomultiplier（R1140P; Hamamatsu
Photonics K.K.）through two condensing quartz lenses

3.2.2 Measurements

and optical filters. Optical filters of BG-39 and HA-50,

The treated samples were measured using a tradi-

and U-340 were used routinely for IRSL and BLSL mea-

tional multiple aliquot additive dose techniquesurements, respectively, although they were exchanged（MAAD）（Aitken, 1985） with the NRL-99-OSTL

readily for the other filters. Though the sample disk canreader. Five aliquots each were used for the measure-

be cooled to as low as -150°C with liquid nitrogen toments of natural and additive-dose samples. When the

suppress the effects attributable to thermal assistantdose dependence of the luminescence intensity is linear,processing of OSL （Hütt et al., 1988）, the measure-measurements for the correction in low-dose region

ments reported herein were taken without using thiswere made with the samples annealed at 350°C for 60

cooling system to avoid rather complicated operatingmin. IRSL measurements were taken at a sample tem-procedures.

perature of 60°C following preheating treatment（160°C

Using a Daybreak TL/OSL 1150 reader, TL mea-for 60 s）. BLSL measurements were made at 120°C fol-surements were taken. In routine TL measurements,

lowing preheating treatment（220°C for 60 s）（Shitaoka

samples are heated from room temperature to 500°C

and Nagatomo, 2001）.

with a heating rate of 10°C/s in an atmosphere of nitrogen. Optical filters of BG-39 and Corning 7-59 or Corn-

3.3 Paleodose estimation using TL procedureing 4-96 were used for TL measurements.

3.3.1 Sample preparation
Quartz coarse-grained samples were extracted from

3.2 Paleodose estimation using OSL procedures

soil and a granite pebble heated by lava flow. A granite

3.2.1 Sample preparation

pebble was first cut with a diamond cutter, revealing

The samples were crushed under water. The finethat the color of the outer part of the stone had

and semi-fine grains were separated roughly fromchanged to red, which was indicative of heating, andcoarse grains by settling in water. The separated frac-that inner part color was unchanged. The outer heatedtions were treated with 10% hydrogen peroxide（H2O2）

portions were cut from the body of the pebble and32

地球環境研究，Vol.19（2017）

were immersed in Hydrofluoric acid（HF）for 2 hr to

HPGe detector is shielded with oxygen-free copper（10remove the outer surface layer of the pebble exposed tomm thick） and low-background lead （10 mm thick）

sunlight. The sample was then gently crushed mechani-

enclosed in a lead box（150 mm thick）. The calibration

cally to obtain grains smaller than 500 µm, with subse-

curves used to obtain the U, Th, and K contents werequent immersion in 2 0 % HCl for 2 hr. The non-produced using five standard rock samples provided bymagnetic fraction of the treated sample was etched in

the Geological Survey of Japan（Ando et al., 1987）. Con-

20% HF for 90 min and was finally washed in 10% ace-tents of U and Th were obtained as an average of thetic acid（CH3COOH）for 2 hr to smooth the grain sur-estimated contents by application of calibration curves

face. The extracted grains had diameters of 75-250 µm.

for the peaks from both pre-Rn and post-Rn nuclides,

The soil sample was pre-treated with 10% H2O2 forpresuming a radioactive equilibrium between them. The

about 16 hr and was then sieved to obtain the 50-250

dose rates were obtained by converting the U, Th, andµm fraction. The latter was immersed in 20% HCl for 2

K contents applying the data given by Adamiec andhr and passed through a Frantz-type magnetic separa-

Aitken （1998）. The water contents of the samples

tor. The non-magnetic fraction was etched in 20% HF（weight of water/dry weight）were used for the con-for 90 min. Subsequently, the treated material was

version（Zimmerman, 1977）.

washed in concentrated HF（46%）for 1 min to remove

The beta dose rates were measured separately

the minerals other than quartz. The quartz mineralusing the sample itself and a TL dosimeter （TLD）

grains which were finally obtained were of 75-250 µm（Ichikawa et al., 1982）. The sample was crushed into

diameter.

grains of about 50 µm and then pressed into two disksof 50 mm diameter and 5 mm thickness. The TLD

3.3.2 Measurements

powders（Matsushita, CaSO4:Tm）of ca. 100 µm were

The treated samples were measured using MAAD

spread in a monolayer between two disks, shielding

technique with a Daybreak TL/OSL 1150 reader. The

alpha particles from the sample with a 3.5 mg/cm2

samples were heated from room temperature to 500°C

thick polyethylene sheet. Then the disks were put in a

in a nitrogen atmosphere. For the pebble sample, the

200 mm thick lead box for about three weeks. The betadose response of TL using BG-39 and Corning 7-59 fil-dose rate was estimated from the TL intensity of theters was not clear. TL measured using a Corning 4-96

TLD powder, which was given a known dose by afilter showed linear dose response. The TL of soil sam-

Third National Standard 60Co source at Hiroshima Uni-

ples was measured using optical filters of BG-39 andversity.

Corning 7-59. Five aliquots each were used for mea-

The beta dose rates estimated from the contents ofsurements of natural and additive-dose samples in theradioactive elements were compared with thosesame manner as those used for OSL measurements.

obtained by TLD. The difference of dose rates esti-

The dose dependences of the TL intensities for bothmated using the two methods was found to be less thanpebble and soil samples were linear. The samples

10%. This fact implies that the alpha and gamma doseannealed at 350°C for 60 min were used for measure-rates estimated from the contents of radioactive ele-ments for nonlinearity correction in the low-dose

ments were also estimated reasonably, although theregion.

possibility of Rn emanation should be examined. The
dose rate of cosmic rays was assumed as 0.10 mGy/a.

3.4 Dose-rate estimation

For IRSL measurements using semi-fine grained

Alpha, beta, and gamma dose rates were calculated

samples, reduction of the alpha dose rate because ofusing published conversion factors and measured con-attenuation of alpha particles should be corrected

centrations of U, Th, and K obtained using a low-back-because the surfaces of the semi-fine grains were notground gamma-ray spectrometer with a high-purity Ge

removed by HF treatment. The overall correction fac-

（HPGe）detector（EGSP 8785; Eurisys Mesures）. The

tor for alpha, beta, and gamma dose rates is extremely33Geomorphological development at Paleolithic sites of Imjin River Region, Korea, inferred from luminescence dating（Shitaoka et al.）small, e.g. 2% for a 50 µm grain size（Nagatomo et al.,above the artifact horizon（see Table 2）, are younger

2004）
.

than those of Chongokri-b collected from the artifact
horizon. Vasilchuk et al.（2002）reported that their

4. Results of luminescence dating
The examples of IRSL, BLSL, and TL measurements

results of radiocarbon（14C）dating are reversed tothe stratigraphical order at this location, i.e., 31,500±
600 aBP, 31,000±600 aBP, and 25,700±3,000 aBP for

are presented in Fig. 3: the luminescence intensities are
given as a function of added doses. Although the data
are scattered, the response of luminescence intensities
to added doses can be regarded as linear, and measurements for the nonlinearity correction, e.g. supralinearity, were conducted. The results of measurements,
paleodoses, dose rates and luminescence ages are presented in Table 3. For IRSL measurements with polymineral fine grains, which comprise feldspars, thefading of IRSL intensities after irradiation was observed
for five months. Although the observation period wasrather short, notable fading was not found for the samples.
Luminescence dating results for respective sites arelisted below.
Jangsanri site: Samples Jangsanri-a, Jangsanri-b, andJangsanri-c, respectively correspond to samples 3, 4,
and 5 in the reference by Yi（2004）. The altitudes
above mean sea level（a.m.s.l.）of the samples wereca. 39.4 m, 39.0 m, and 38.8 m, respectively, for Jangsanri-a, -b, and -c. All samples were measured by
IRSL with fine grains and show almost identical age.
No fading of IRSL intensities was observed within
five months for these samples.
Chongokri site: The luminescence ages of two samples,
Chongokri-a and Chongokri-b from the N8E16 grid,are consistent with the stratigraphy. Results obtained
for these samples from IRSL measurements withpolymineral fine grains are about 25% younger thanthose by BLSL with quartz fine grains. The possibility of long-term fading of feldspars in polymineral finegrains is considered.
The luminescence age of Chongokri-2 shows it to be
the youngest among the samples of Chongokri-1, -2,
and -3 collected at the same E55S20-IV grid, although
the Chongokri-2 horizon is lower than the Chongokri-1 horizon（see Notes in Table 3）. Furthermore,these samples, which were collected from the layers
34

Fig. 3O
 SL and TL growth curves as a functionof added doses:（a）Kawoli-3, IRSL;（b）Chongokri-b, BLSL; and（c）Tongiri, TL.

地球環境研究，Vol.19（2017）

Table 3

Results of OSL and TL dating for the sediments and a pebble and soil heated bybasalt lavas.

SamplePaleodose Dose rate Luminescence age（Gy） （mGy/a）（ka）MethodNotes

Jangsanri-a

1,260±140

6.11±0.22210±20FG/IRSL

Lower layer of artifact
horizonJangsanri-b

1,230±140

5.57±0.18

220±30FG/IRSL

Lower layer of artifact
horizonJangsanri-c

1,190±230

5.49±0.19220±40Chongokri-a（N8E16 grid）

370±60480±80410±50550±100450±140490±70450±110370±90490±410460±2304.79±0.17

Kawoli-1(Loc. 2, TP19 grid)260±605.53±0.1547±11Semi-FG/IRSLUpper layer of artifact
horizonKawoli-2(Loc. 2, TP19 grid)

440±1305.57±0.1479±24Semi-FG/IRSL

Lower layer of artifact
horizonKawoli-3(Loc. 3)230±100

4.36±0.09

52±23

Semi-FG/IRSLUpper layer of artifact
horizonKawoli-4(Loc. 3)n. d.

5.29±0.18

n. d.

Semi-FG/IRSL

Llower layer ofartifact horizon

Kumpari-1(S60W380 grid)

130±100

6.12±0.3122±17FG/IRSL

Artifact horizon

280±406.20±0.2245±7FG/IRSL

Llower layer ofartifact horizon

960±300
610±805.21±0.16
3.92±0.18

180±60160±20

CG/TL
CG/TL

Chongokri-b（N8E16 grid）
Chongokri-1(E55S20-IV grid)
Chongokri-2(E55S20-IV grid)
Chongokri-3(E55S20-IV grid)

Kumpari-2(S60W380 grid)Baekuiri，pebble
Tongiri, soil

4.81±0.09
4.15±0.08

5.12±0.17
5.17±0.17

76±13
99±16
99±12
130±2093±29
100±10
88±21
73±18
94±80
88±45

Lower layer of artifact
horizon
FG/IRSL Upper layer of artifact
horizonQuartz-FG/BLSL
FG/IRSL
Artifact horizon
FG/IRSL

Quartz-FG/BLSL

FG/IRSL
Quartz-FG/BLSL

FG/IRSL
Quartz-FG/BLSL

FG/IRSL
Quartz-FG/BLSL

58 m (a.m.s.l)
56.5 m (a.m.s.l)
56 m (a.m.s.l)FG, fine grains; Semi-FG, semi-fine grains; Quartz-FG, quartz fine grains; and CG, coarse grains. IRSL,
infra-red stimulated luminescence; BLSL, blue-light stimulated luminescence; and TL, thermoluminescence. n.d., not determined.

the horizon of a.m.s.l. 61.6 m, 21,950±200 aBP for thatorder.

of a.m.s.l. 60.2 m, and 16,100±300 aBP for that of

Baekuiri and Tongiri outcrops: TL ages of the pebble

a.m.s.l. 58.05 m. This reversal might be attributable toand soil sample heated by basalt lavas are regarded

the disturbance of soil caused by cracks observed inas obtained successfully because only the apparently

the strata of this grid.

well-baked samples were used for the present mea-

Kawoli site: The luminescence ages of two samples,surements.

Kawoli-1 and Kawoli-2, from locality 2（TP19 grid）
are consistent with the stratigraphical order. Data forthe sample, Kawoli-4 from the locality 3 were dispersed and luminescence age could not be determined.

5. Discussion
5.1 Geomorphological development of the Imjin-

This result might be attributable to incomplete or

Hantan Valley

insufficient zeroing caused by the depositional condi-

The baked pebble and soil below the basalt lava

tion.

were dated back to 160 - 180 ka using TL measure-

Kumpari site: Results for the artifact horizon and thements. The sediments that intercalate Paleolithic arti-

clay below it are consistent with the stratigraphicalfacts, overlying the basalt lava, were also dated back to
35

Geomorphological development at Paleolithic sites of Imjin River Region, Korea, inferred from luminescence dating（Shitaoka et al.）ca. 30 - 100 ka. We reconstructed the geomorphologicalevolution of Imjin-Hantan valley where Paleolithic sites
were located on the basalt-lava terrace and higher terrace, based on the dating results.

6. Conclusion
Sediments from four Paleolithic sites and a pebble
and soil underlying the basalt lava flows at two out-

The basalt lava of high fluidity erupted and flowed

crops along the Imjin River and Hantan River in Korea

into the Imjin-Hantan valley in ca. 100 - 200 ka. The

were tested using OSL and TL dating methods. The TL

lava flow reached as far downstream as Kumpari, dam-ages of the burnt pebble and baked soil, ca. 180 ka andming those rivers around Chongokri. A temporary lake

160 ka, suggest that the influx of lava occurred about

presumably appeared along the paleo-Hantan River and

150 ka before present. The IRSL and BLSL ages for

the Yongpyong River upstream of the natural dam

samples from Chongokri, Kawoli, and Kumpari sites, ca.

because lacustrine of silty or clayey deposits underlies

100 ka, 60 ka, and 30 ka, respectively, suggest that thein the Yongpyong River Basin. Subsequent overflow

Paleolithic occupation occurred after deposition of aeo-

from the dam caused resumption of the incision on tolian and fluvial soil deposits on the lava flow. The Jang-the basalt lava along the present river course of thesanri site located on the river terrace might dateImjin River, forming the lava strath terrace and lower

earlier than the inflow of the lava of high fluidity thatfluvial terraces. During such geomophological processes,

reached Kumpari. Although evidence is lacking with

Paleolithic stones, as remnants of the humans habita-

the wide range of the ages for the basalt lavas as dem-tion, were intercalated in the aeolian and flood deposits

onstrated in Table 1, it might be true that the basalt

overlying the basalt lava and lava strath terraces.

lava moved rapidly down the valley system in several

Development of the higher terrace occurred earlier

episodes. Humans at Chongokri, Kawoli, and Kumpari

than that of the basalt-lava terrace, considering the geo-sites occupied the areas after the lava inflow of ca. 100 -morpho-chronological positions between them. Such a

200 ka, and Jangsanri site before the lava inflow.

geomorphological sequence is confirmed by the TL and
OSL ages obtained from Jangsanri site and the basalt
lava. Jangsanri site, located on the higher terrace that

Acknowledgments:

occurs in the lower stream side than Kumpari, was

The authors are grateful to Prof. Bailiff, I.K. at Dur-dated back to over 200 ka. Furthermore, the ages of the

ham University for his valuable comments on the text.

basalt are ca. 100 - 200 ka.

The present work was partly supported by a Grant-inAid for Fundamental Research from the Japan Society

5.2 Implications for human occupation of thefor the Promotion of Science （No. 15200059 andImjin-Hantan valley

25702011）. Fieldwork in Korea was supported by the

A notable finding of this study is that humans had

Interdisciplinary Research Grant of the Seoul Nationalalready appeared in this valley before the inflows of the

University, 2003 and 2004.

basalt lavas. They had resettled the region despite thecatastrophic environmental events. Although evidence

Referencesis lacking for the wide range of the ages for the basalt

Adamiec, G. and Aitken, M.J., 1998: Dose-rate conversion

lavas, as presented in Table 1, it might be true that thebasalt lava moved rapidly down the valley system inseveral episodes. Consequently, some undetected Paleolithic sites might lie underneath these flows. Humans at
Chongokri, Kawoli, and Kumpari sites occupied the site
after the lava inflow of ca. 100 - 200 ka, and the Jangsanri site before the lava inflow.

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36

地球環境研究，Vol.19（2017）
Bae, K., 2002: Chongokni Paleolithic Site; Current under-tion factor for alpha dose rate in luminescence dating withstandings. Paleolithic Archaeology in Northeast Asia.

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Geomorphological development at Paleolithic sites of Imjin River Region, Korea, inferred from luminescence dating（Shitaoka et al.）

ルミネッセンス年代測定から検討した臨津江流域の旧石器遺跡に関する地形形成の変遷
下

岡

順

直＊

長

友

恒

人＊＊

八

木

浩

司＊＊＊

李

鮮

鰒＊＊＊＊

立正大学
奈良教育大学名誉教授
＊＊＊
山形大学
＊＊＊＊
ソウル大学校＊＊＊要旨：
臨津江 ・ 漢灘江流域の両岸を形成する玄武岩溶岩の年代測定は、これまで K-Ar や FT 年代測定など理化学的年代測定によって行われ、0.85～0.1 Ma という幅の広い結果が得られてきた。そして、これら結果を精査すると、溶岩は複数回流れた可能性があることがわかった。しかし、いまだ確定的な年代結果は得られていないのが現状である。そのため、玄武岩溶岩の上層にある堆積層から検出される旧石器遺跡の年代を求めることができなかった。
本研究では、玄武岩溶岩の上層にある堆積層の OSL 年代測定、および玄武岩溶岩直下の溶岩によって焼けた土壌や石の TL 年代測定を行った。その結果、旧石器が検出される堆積物は約30～100 ka、焼けた土壌や石は約160～180 kaのルミネッセンス年代を求めた。また、高位段丘上に位置する長山里旧石器遺跡は、約200 ka の年代値が求められた。この遺跡は臨津江の下流に位置し、約160～180 ka の溶岩が流れてくる以前に形成された旧石器遺跡であることがわかった。
キーワード： 旧石器遺跡、臨津江、地形形成、玄武溶岩、ルミネッセンス年代測定、大韓民国

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