Late Pleistocene marine terraces formed during interglacial sea-level highstands are widely distributed across the Japanese islands. Tephrochronology has been used to correlate these terraces with marine isotope stages (MIS) (Machida and Arai, 2003). Ages of marine terraces formed during the last interglacial (MIS 5e; 123 ± 7 ka) are well defined in many places (e.g., Koike and Machida, 2001) by widely distributed marker tephras. Marker tephras, such as Ontake Pm1 (On-Pm1, 95.7 ± 5.3 ka, Aoki
Optically stimulated luminescence (OSL) dating of quartz has been widely applied to date coastal and marine sediments (Jacobs, 2008). In Japan, Tanaka
Thomsen
In this study, we investigated pIRIR290 signals obtained after different first IR stimulation temperatures from K-feldspar from marine terrace deposits in northeastern Japan that formed during the last interglacial. For each different first IR stimulation temperature, we measured
The Kamikita coastal plain, which lies along the Pacific coast at the northeastern end of Honshu Island, is about 50 km long and 30 km wide (Fig. 1). The plain has six marine terrace surfaces, named the Higher (Fukuromachi) (elevation, 110–220 m), Shichihyaku (90–110 m), Tengutai (45–80 m), Takadate (30–40 m), Nejo (10–15 m), and Shibayama (<10 m) surfaces, and two levels of fluvial terraces, the Shichinohe and Sanbongi (<5 m) surfaces (Miyauchi, 1985, 1987; Koike and Machida, 2001). The northeastern part of the Kamikita plain is occupied by Lake Ogawara, an irregularly shaped body of water that is generally elongated parallel to the coast. Seaward of the lake, only the Takadate terrace and the two fluvial terraces have been mapped. The Holocene plain is distributed only along the rivers draining into the lake and the lake’s outlet to the sea, and is not extensively developed along the modern shoreline.
(a) Location map of the Kamikita coastal plain, northeastern Japan. (b) Map showing the distribution of Late and Middle Pleistocene marine terraces and sampling sites (after Miyauchi, 1985, 1987). In the legend, surface is abbreviated a “S” The elevation range of each terrace is given in the text. (c) Digital elevation model of the Kamikita coastal plain based on 10-m-grid data from the Geospatial Information Authority of Japan. Lighter grays indicate lower elevations, and darker grays and black indicate higher elevations.Fig. 1
The age of the Takadate terrace is constrained by the presence of the Toya tephra, which has been dated to 112–115 ka by a combination of fission track dating, thermoluminescence (TL) dating, and stratigraphy (Machida and Arai, 2003), and to 104 ± 15 to 118 ± 15 ka by red TL dating (Ganzawa and Ike, 2011). Shirai
We investigated two outcrops (sites 1 and 2) at the landward edge of the Takadate terrace, facing Lake Ogawara (Fig. 1). Depositional facies of the outcrops were defined and interpreted based on sedimentary structures and grain size. The elevations of the facies boundaries were measured with a virtual reference station GPS (Leica Viva GS08plus, Leica). These outcrops are 330 m apart and appear to expose laterally continuous deposits. The depositional succession beneath the Takadate terrace consists of lower subtidal facies and an upper terrigenous deposit, both of which were sampled. Light-tight black PVC tubes 15 cm long and 5 cm in diameter were hammered into the outcrop to sample sediment unexposed to light. Modern beach sand (sample gsj14-019) was collected at site 3 (Fig. 1) to determine the residual dose. This sample was obtained from
The subtidal facies at site 1 consists of fine to coarse sand containing granules and pebbles (Fig. 2). The lower part of the unit, 8 m thick, consists of cross-laminated gravelly coarse sand alternating with cross-laminated fine to medium sand. The coarse sand contains wave dunes and the fine sand contains burrows. This assemblage reflects the dominance of storm-wave sedimentation in the lower shoreface (Walker and Plint, 1992; Cummings
Columnar sections from sites 1 and 2. Grain size is categorized into clay, silt, very fine sand, fine sand, medium sand, coarse sand, very coarse sand, granules, and pebbles (C, Si, vfs, fs, ms, cs, vcs, G, and P, respectively). The bold horizontal line represents the erosional surface between the terrestrial and subtidal facies deposits. T.P. (Tokyo Peil) is the standard datum for elevation measurements in Japan.Fig. 2
The terrigenous unit at site 1 consists of alternating sand and brownish silt. The silt layers are poorly sorted and contain sand and granules, and their brownish color indicates that they are loess beds or paleosols. A few unidentified tephra layers are intercalated with the silt layers. The sand layers are 30 cm to 200 cm thick and characterized by well-defined cross- to horizontal laminations. A 2-m-thick sand layer in the upper part of the unit exhibits aeolian dune stratification dipping eastward in the direction of the winter monsoon winds in this region. Other sand layers also probably represent aeolian dunes or sand sheets, because they are interbedded with paleosols.
We took four sediment samples for luminescence dating from different levels of the lower shoreface deposits (gsj14-017, gsj14-029, gsj14-030, and gsj14-031), three samples from one level of the upper shoreface deposits (gsj13-039, gsj14-014, and gsj14-015), and one sample from aeolian sand deposits (gsj13-040).
The subtidal facies at site 2 consists of coarsening-upward regressive shoreface deposits similar to those at site 1. Its erosional upper boundary is at 18.0 m elevation, suggesting slightly deeper erosion than at site 1. The terrigenous unit, as at site 1, is composed of aeolian sand and brownish paleosols, but its uppermost part is dominated by 9-m-thick aeolian dune deposits showing east-dipping cross-lamination. The same aeolian dune extends along the eastern shoreline of Lake Ogawara (Fig. 1; Miyauchi, 1985, 1987).
Samples for luminescence dating were taken from three levels of the lower shoreface deposits (gsj13-091, gsj13-095, and gsj13-096), from two levels of the upper shoreface deposits (gsj13-092 and gsj13-094), and from one level of the aeolian sand deposits (gsj13-093).
The two subtidal facies, upper shoreface and lower shoreface, accumulated under different water depths and during different time periods and thus have different sedimentation ages. In Denmark, Fruergaard
All samples were processed and measured at the luminescence laboratory of the Geological Survey of Japan. Sediment within 3 cm from each end of the tube, which may have been exposed to sunlight during sampling, was removed and used for measuring moisture content and dosimetry. The remaining sediment was processed to extract coarse grains of K-rich feldspar. The samples were treated with 10% HCl and 10% H2O2 to dissolve carbonate and organic matter, respectively, and then screened using 180 μm and 250 μm mesh sieves. Finally, the K-rich feldspar fraction (
Luminescence signals were measured with a TL-DA-20 automated Risø reader equipped with infrared LEDs for stimulation (145 mW/cm2; central wavelength, 870 nm) and a 90Sr/90Y beta source (dose rate,
The contributions of natural radioisotopes and cosmic radiation were considered in the determination of the annual dose rate. After mixing and homogenization of the dried sample, radioisotope concentrations were measured by inductively coupled plasma mass spectrometry and converted to dose rates by using the conversion factors of Guérin
Radioisotope concentration, water content, cosmic ray and dose-rate for sediment samples. Listed water content was natural value. The water content for dose rate calculation was estimated from the mean of natural and saturated (31.0%) water contents. For details see main text.Sample Depth (m) Radioisotope concentraion Water Content (%) Cosmic Dose Rate (Gy/ka) Dose-rate (Gy/ka) K (%) Rb (ppm) Th (ppm) U (ppm) gsj13-040 7.40 0.62 ± 0.06 20.8 ± 2.1 1.35 ± 0.14 0.38 ± 0.04 3. 0 0.10 1.57 ± 0.12 gsj14-014 8.30 0.68 ± 0.07 23.2 ± 2.3 1.55 ± 0.16 0.44 ± 0.04 7.3 0.09 1.62 ± 0.12 gsj14-015 8.30 0.72 ± 0.07 23.1 ± 2.3 1.85 ± 0.19 0.48 ± 0.05 9.3 0.09 1.67 ± 0.12 gsj13-039 8.30 0.77 ± 0.08 19.9 ± 2.0 1.60 ± 0.16 0.44 ± 0.04 11.3 0.09 1.67 ± 0.12 gsj14-031 11.54 0.83 ± 0.08 24.9 ± 2.5 1.67 ± 0.17 0.52 ± 0.05 16.1 0.07 1.70 ± 0.12 gsj14-030 14.47 0.88 ± 0.09 24.1 ± 2.4 2.09 ± 0.21 0.60 ± 0.06 20.2 0.06 1.75 ± 0.12 gsj14-017 17.60 0.69 ± 0.07 23.1 ± 2.3 2.46 ± 0.25 0.46 ± 0.05 15.7 0.04 1.60 ± 0.11 gsj14-029 17.61 0.78 ± 0.08 22.9 ± 2.3 2.34 ± 0.23 0.74 ± 0.07 24.1 0.04 1.69 ± 0.12 gsj13-093 11. 84 0.50 ± 0.05 19.2 ± 1.9 1.63 ± 0.16 0.46 ± 0.05 11.4 0.07 1.44 ± 0.10 gsj13-094 13.80 0.52 ± 0.05 18.0 ± 1.8 1.30 ± 0.13 0.37 ± 0.04 11.2 0.06 1.41 ± 0.10 gsj13-092 14.08 0.71 ± 0.07 25.5 ± 2.6 1.93 ± 0.19 0.58 ± 0.06 17.7 0.06 1.61 ± 0.11 gsj13-095 16.07 0.69 ± 0.07 24.9 ± 2.5 1.82 ± 0.18 0.52 ± 0.05 19.2 0.05 1.57 ± 0.11 gsj13-091 17.33 0.55 ± 0.06 22.1 ± 2.2 1.80 ± 0.18 0.47 ± 0.05 10.3 0.05 1.48 ± 0.11 gsj13-096 18.03 0.73 ± 0.07 24.3 ± 2.4 1.94 ± 0.19 0.54 ± 0.05 18.7 0.04 1.60 ± 0.11 gsj14-019 0.10 0.18 ± 0.02 6.2 ± 0.6 0.79 ± 0.08 0.22 ± 0.02 5.9 0.21 1.50 ± 0.10
Using gsj13-039 and gsj13-094, we investigated the characteristics of pIRIR290 signals with different first IR stimulation temperatures. The pIRIR stimulation temperature and preheat temperature were fixed at 290°C and 320°C, while the first IR stimulation temperature was varied between 50°C and 250°C with a 50°C increment. The luminescence signal was measured in 0.1-s bins. The decay curves of the five plRIR signals from gsj13-039 are shown in Fig. 3a. The highest intensity was that of the pIRIR50/290 signal at
pIRIR signal characteristics of samples gsj13-039 and gsj13-094 with different first IR stimulation temperatures. The pIRIR stimulation and preheat temperatures were fixed at 290 and 320°C, respectively. (a) Typical signal intensities of pIRIR290 signals from sample gsjl3-039, (b) first IR stimulation temperature plateau, and (c) dose recovery ratio and residual dose after bleaching for 3 h with different first stimulation temperatures. The error bars show one standard error. In (b), the bold and dashed lines represent the average De of each sample, except for De at the first IR measurement temperature of 250°C for gsj13-039. In (c), the dashed lines represent the ±10% range.Fig. 3
Buylaert
Single aliquot regenerative (SAR) protocol used for De measurements.Step Measurement Protocol 1 Give dose 2 Preheat 320°C for 60 s 3 IRSL 50, 100, 150, 200, 250°C for 200 s 4 IRSL 290°C for 200 s (pIRIR50/290, pIRIR100/290, pIRIR150/290, pIRIR200/290, pIRIR250/290) 5 Give test dose 6 Preheat 320°C for 60 s 7 IRSL 50, 100, 150, 200, 250°C for 200 s 8 IRSL 290°C for 200 s (pIRIR50/290, pIRIR100/290, pIRIR150/290, pIRIR200/290, pIRIR250/290) 9 Hot IR bleach for 200 s at 325°C 10 Return to step 1
A dose recovery test was performed using at least six aliquots from each sample. Aliquots were exposed for 3 h to artificial sunlight in a UVACUBE 400 chamber (Hönle) with a SOL 500 lamp module at a lamp-to-sample distance of 50 cm. After this bleaching, half of the aliquots were given a dose of β-radiation nearly equal to each
It has been suggested that the fading of the pIRIR290 signal is negligible in nature, because in very old samples measured by some studies the natural signal was close to the saturation level (Buylaert
In this study, we performed a fading test with different first IR stimulation temperatures using gsj13-039 and gsj13-094 to check the signal stability of our samples (Fig. 4). Additionally, for gsj13-040, gsj13-030, gsj13-093, and gsj13-095, we performed a fading test for pIRIR290 with first stimulation temperatures of 50°C and 200°C (Table 3). Our fading test protocol was based on Auclair
Fading test results. (a) Typical results for sample gsj13-039; (b) g-values obtained with different first IR stimulation temperatures for gsj13-039 and gsj13-094. The error bars show one standard error.Fig. 4
Results of pIRIR dating using different first IR stimulation temperatures. n is number of aliquots, ρ′ is the dimensionless recombination center density (Huntley, 2006). Residual dose was De after artificial sunlight bleaching for 3 h except for modern beach sand (gsj14-019) which was bleached for 800 h. Fading correction was performed based on Kars et al. (2008) and Kars and Wallinga (2009). To calculate the uncorrected ages, residual dose of modern beach sand (gsj14-019) was subtracted from De of each sample. D0 values were calculated based on Wintle and Murray (2006). aTerrigenous sediments. bIf the average g-value of samples from site 2 was lower than zero, fading correction would not performed.Sample Measurement procedure n Fading test Dose recovery test Fading-uncorrected Age (ka) Fading-corrected Ageb (ka) D0 (Gy) n g2days (%/decade) ρ′ /10−6 n Dose recovery ratio n Residual dose (Gy) gsj13-040a pIRIR50/290 11 96 ± 3 11 2.19 ±0.09 2.24 ±0.10 3 0.93 ± 0.09 3 10± 1 59 ± 5 95 ±9 361 pIRIR200/290 17 120 ± 4 7 −1.02 ±0.73 −1.11 ±0.72 3 1.07 ± 0.09 3 12 ± 6 74 ± 7 81 ±8 251 gsj14-014 pIRIR50/290 8 163 ± 8 3 1.16 ± 0.05 3 15 ± 1 99 ± 11 167 ±20 413 pIRIR200/290 11 192 ± 5 3 1.20 ± 0.10 3 25 ± 1 116± 10 127 ± 12 324 gsj14-015 pIRIR50/290 8 178 ± 8 3 1.06 ± 0.03 3 12 ± 0 105 ± 10 168 ± 16 724 pIRIR200/290 8 181 ± 6 3 0.81 ± 0.05 3 22 ± 1 106 ± 10 116 ± 11 392 gsj13-039 pIRIR50/290 28 176 ± 8 28 1.65 ±0.18 1.64 ±0.17 10 1.03 ± 0.10 6 15 ± 0 103 ± 10 177 ±20 422 pIRIR100/290 12 191 ± 10 12 2.22 ± 0.34 2.22 ± 0.33 9 1.10 ± 0.12 6 18 ± 2 112 ± 12 199 ±25 424 pIRIRI50/290 10 200 ±7 10 1.65 ±0.31 1.64 ±0.31 9 1.06 ± 0.12 6 23 ± 2 118 ± 11 178 ± 17 451 pIRIR200/290 19 183 ± 14 19 0.49 ± 0.46 0.48 ± 0.49 12 1.02 ± 0.11 12 27 ± 2 107 ± 15 117 ± 17 370 pIRIR250/290 9 238 ± 8 9 −0.26 ± 1.07 −0.42 ± 1.15 9 1.08 ± 0.40 6 28 ± 7 139 ± 15 139 ± 15 231 gsj14-031 pIRIR50/290 7 163 ± 7 3 1.06 ± 0.05 3 13± 1 94 ± 9 159 ± 16 410 pIRIR200/290 9 194 ± 7 3 1.01 ± 0.07 3 25 ± 1 112 ± 12 123 ± 13 298 gsj14-030 pIRIR50/290 8 204 ± 5 8 2.53 ± 0.31 2.53 ± 0.32 3 1.04 ± 0.05 3 15 ± 0 116± 9 199 ± 17 448 pIRIR200/290 13 214 ± 7 12 1.57 ±0.40 1.57 ±0.40 3 0.94 ± 0.17 3 31 ± 1 120 ± 12 133 ± 14 258 gsj14-017 pIRIR50/290 8 184 ± 5 3 1.04 ± 0.05 3 16± 1 113± 9 188 ± 16 514 pIRIR200/290 11 204 ± 11 3 1.02 ± 0.07 3 31 ± 1 125 ± 14 136 ± 15 446 gsj14-029 pIRIR50/290 8 183 ± 5 3 0.96 ± 0.04 3 14 ± 1 107 ± 9 181 ± 15 453 pIRIR200/290 10 206 ± 9 3 1.01 ± 0.10 3 21 ± 1 120 ± 13 131 ± 15 339 gsj13-093a pIRIR50/290 10 95 ± 2 10 1.25 ±0.66 1.21 ±0.66 3 1.09 ± 0.05 3 11 ± 0 64 ± 5 94 ±8 371 pIRIR200/290 16 127 ± 4 8 −1.34 ±0.57 −1.43 ±0.62 3 1.13 ± 0.10 3 21 ± 2 86 ± 8 229 gsj13-094 pIRIR50/290 17 163 ± 6 11 2.21 ± 0.42 2.24 ± 0.40 3 1.16 ± 0.07 3 19 ± 1 114 ± 10 173 ± 16 461 pIRIR100/290 6 203 ± 7 6 0.55 ±0.14 0.58 ±0.15 3 1.11 ± 0.05 3 18 ± 1 142 ± 13 164 ± 16 420 pIRIR50/290 6 210 ± 4 6 1.50 ±0.23 1.52 ±0.25 3 0.98 ± 0.09 3 20 ± 1 147 ± 12 223 ± 18 364 pIRIR200/290 24 193 ± 7 12 −0.11 ±0.74 −0.20 ± 0.76 3 1.02 ± 0.07 3 31 ± 1 134 ± 14 324 pIRIR250/290 4 221 ± 14 4 0.81 ± 0.57 0.83 ± 0.59 3 0.65 ± 0.07 3 38 ± 3 154 ± 27 202 ± 41 253 gsj13-092 pIRIR50/290 7 205 ± 5 3 1.08 ± 0.06 3 17 ± 0 126 ± 10 193 ± 16 507 pIRIR200/290 10 219 ± 3 3 1.02 ± 0.07 3 31 ± 1 134 ± 10 287 gsj13-095 pIRIR50/290 8 193 ± 5 8 1.82 ±0.12 1.82 ±0.13 3 1.16 ± 0.07 3 12 ± 0 121 ± 10 187 ± 16 450 pIRIR200/290 16 214 ± 4 12 1.40 ±0.22 1.40 ±0.23 3 0.97 ± 0.06 3 28 ± 1 134 ± 11 354 gsj13-091 pIRIR50/290 8 178 ± 3 3 1.07 ± 0.06 3 16± 1 118 ± 9 178 ± 14 532 pIRIR200/290 11 205 ± 5 3 1.13 ± 0.12 3 32 ± 2 136 ± 12 312 gsj13-096 pIRIR50/290 8 187 ± 13 3 1.06 ± 0.06 3 11 ± 1 115 ± 15 177 ±26 442 pIRIR200/290 12 202 ±7 3 1.15 ± 0.06 3 27 ± 1 123 ± 12 339 gsj14-019 pIRIR50/290 12 16± 2 3 3 ± 0 pIRIR100/290 8 14 ± 2 pIRlR50/290 8 11 ± 1 pIRIR200/290 15 17 ± 1 3 4 ± 0 pIRIR250/290 8 26 ± 2
It is well known that the pIRIR signal is much more difficult to bleach than the IR50 signal (e.g., Buylaert
Average residual dose obtained for different artificial sunlight bleaching times. Each data point represents the average of at least six aliquots. The error bars show one standard error.Fig. 5
The fading uncorrected ages obtained with different first IR stimulation temperatures from gsj13-039 and gsj13-094 are shown in Fig. 6a and Table 3, and those of the pIRIR50/290 and pIRIR200/290 signals from the samples from the subtidal facies deposits are shown in Fig. 7. The uncorrected ages of gsj13-039 with different first IR stimulation temperatures are generally consistent with the expected age (MIS 5e, 123 ± 7 ka), with a possible exception of the pIRIR50/290 signal (Fig. 6a). On the other hand, the uncorrected gsj13-094 ages of pIRIR100/290, pIRIR150/290 and pIRIR250/290 signals are slightly older than the expected age if we do not consider the large scatter of own age. The uncorrected ages of the pIRIR200/290 signals of all samples (Fig. 7) were concordant with the expected age. The uncorrected ages of the pIRIR50/290 signal from the samples from site 2 were also concordant with the expected age, but the ages of the pIRIR50/290 signal from four samples from site 1 were underestimated.
(a) Uncorrected and (b) corrected pIRIR ages of gsj13-039 and gsj13-094 obtained with different first IR stimulation temperatures. The error bars show one standard error.Fig. 6
Columnar sections as in Fig. 2. For sites 1 and 2, the fading-uncorrected and -corrected ages of the PIRIR50/290 and PIRIR200/290 signals are shown with one standard error. For site 2, the fading corrected ages of PIRIR200/290 signals were not calculated because the average ρ’ value was lower than zero. For each site, the vertical gray bar shows the expected age range. T.P. (Tokyo Peil) is the standard datum for elevation measurements in Japan.Fig. 7
In the previous section, we showed that fading rates of the pIRIR50/290 signal were positive in all samples whereas the fading rates of the pIRIR200/290 signal were smaller and consistent with zero in four samples (taking account of the 2-σ uncertainty).
To apply the fading correction, it is necessary to consider the shape of the dose–response curve. If a
Typical dose–response curve for the PIRIR50/290 and PIRIR200/290 signals of sample gsj13-039.Fig. 8
The corrected ages are shown in the same way as the uncorrected ages (Figs. 6b and 7). Except for the pIRIR200/290 signals, the corrected ages with different first IR stimulation temperatures overestimated the expected age. The corrected ages of the pIRIR200/290 signals of samples from site 1, like the uncorrected ages of the pIRIR200/290 signals of all samples, were concordant with the expected age (Fig. 7). On the other hand, the corrected ages of the pIRIR50/290 signals from all samples were always older than the expected age. The characteristic saturation dose (D0) values of our dose–response curves were calculated based on Wintle and Murray (2006) (Table 3). The resultant D0 values, generally ranging between 300 and 500 Gy, were lower than the D0 values of pIRIR50/225 and pIRIR50/290 signals reported by Li
In this study, both fading-uncorrected and -corrected pIRIR200/290 ages in site 1 were shown to be in agreement with the expected age. When we compared the uncorrected and corrected pIRIR200/290 ages, the corrected ages showed a much narrower age cluster around the expected age of 123 ± 7 ka, presumably because of a small fading influence. We conclude that the fading-corrected pIRIR200/290 ages are most suitable, if a positive ρ’ value is calculated.
The fading-corrected and -uncorrected ages of the pIRIR200/290 signals of our terrigenous samples (gsj13-040 and gsj13-093) were 81 ± 8 ka and 86 ± 8 ka, respectively, whereas the corrected ages of the samples from the subtidal facies ranged from 116 ± 11 ka to 136 ± 15 ka. The field evidence showed that the terrigenous sediments accumulated after the deposition of the subtidal facies and were separated from them by an erosional surface. These ages indicate that the terrigenous sediment was deposited during MIS 5a. In the samples from the subtidal facies, we found no systematic stratigraphic trend of the pIRIR200/290 ages. This concentration of ages of the pIRIR200/290 signal is similar to previous results from the Oga Peninsula for the pIRIR50/225 signal (Thiel
The pIRIR dating protocol was applied to marine terrace deposits from the last interglacial on the Kamikita coastal plain, northeastern Japan. To calculate fading-uncorrected ages, the residual dose that was obtained by bleaching of a modern beach sample for 800 h in a solar simulator was subtracted from the