Thermoluminescence Ages Research Articles

Alteration and Thermoluminescence Ages of Altered and Volcanic Rocks in the Hachimantai Appi Geothermal Field, NE Japan

Alteration and Thermoluminescence Ages of Altered and Volcanic Rocks in the Hachimantai Appi Geothermal Field, NE Japan

Taxonomy and palaeoecology of Ostracoda from the Middle to Late Pleistocene upper Karewa formation of Kashmir Valley, Northern India

Abstract. Ostracoda from a 25 m thick exposure in sediments of the upper Karewa formation indicate lacustrine conditions in the Kashmir intermontane basin during the Middle to Late Pleistocene. The Middle to Late Pleistocene age is established on the basis of lithostratigraphy and confirmed by two thermoluminescence age determinations at the top of the section. The ostracod assemblages show that the lake water remained fresh or, at most, was very slightly saline, throughout the period represented by the section. Nearly all ostracod taxa identified from the sediments are cold stenothermal forms and they include inhabitants of the littoral and profundal domain as well as running waters and springs. The Ostracoda present within the section indicate that during deposition of the upper Karewa sediments a large, but fairly shallow, well-oxygenated open-basin freshwater lake existed in that central part of the Kashmir Basin. Although the sequences suggest changes in water depth may have occurred, lacustrine conditions were otherwise largely unchanged over the period represented by the section, up until the demise of the lake during the early part of the Late Pleistocene.

Zeroing tests of luminescence sediment dating in the Arctic Ocean: Review and new results from Alaska-margin core tops and central-ocean dirty sea ice

Additional numeric dating techniques are needed for sediments in the Arctic Ocean that span at least the last half million years. Almost all presently suitable geochronometers are relative-dating methods, requiring significant assumptions about sedimentation rates (such as continuous deposition and preservation). An alternative ‘absolute’ geochronometer, luminescence sediment dating, assumes daylight exposure of siliciclastic grains before burial. Early tests and applications of thermoluminescence (TL) techniques in the western Arctic Ocean showed some promise, but trans-ocean application to core tops of more sensitive photon-stimulated-luminescence (PSL) multi-aliquot procedures revealed large regional variations in accuracy. Recent applications of single-aliquot PSL procedures to core tops and dirty sea ice refine our understanding of the limitations and capabilities of PSL dating in this ocean. Dirty sea ice is the source of most of the bottom sediment. Particular procedures for multi-aliquot and single-aliquot PSL dating produce near-zero ages for silt grains from 4 available dirty sea-ice samples. This suggests that TL and PSL age overestimates obtained previously from core-top samples were due mainly to bottom-current reworking (mixing or stripping) of silt grains in abyssal darkness, rather than due to sedimentation of relict-age grains from sea ice. Single-aliquot PSL dating of silt grains from core tops at two different-depth sites at the Alaskan margin reveals large variations in accuracy. This re-emphasizes the critical sensitivity of fine-silt PSL dating accuracy to the effects of bottom-current processes. These recent applications are beginning to provide a more precise knowledge of just where and how PSL methods are likely to be accurate in the Arctic Ocean.

Investigations of uranium distribution in flints

Thermoluminescence (TL), which is commonly used to date burnt flints from Palaeolithic sites, sometimes yields ages which are younger than those obtained by other methods. Many reasons could explain such discrepancies and one concerns the evaluation of the dose-rate originating from the sample itself, i.e., the internal dose-rate. In order to refine the parameters used in the internal dose-rate estimation, we investigated the uranium (U) distribution by the induced fission track method in three archaeological flint specimens. This approach shows that the U distribution is roughly uniform on a scale of a millimetre but not on a smaller scale (<100 μm), because of the presence of quartz grains whose size is sample-dependent and because of relatively high local U concentrations. Therefore, the assumption of a homogeneous U distribution currently used to estimate the beta and alpha dose-rates may not be fully appropriate for all samples; in this case, this could lead to an underestimate of the TL age.

Late Quaternary erosion events in lowland and mid-altitude Tasmania in relation to climate change and first human arrival

The establishment of a chronology of landscape-forming events in lowland and mid-altitude Tasmania, essential for assessing the relative importance of climatic and human influences on erosion, and for assessing present erosion risk, has been limited by the small number of ages obtained and limitations of dating methods. In this paper we critically assess previous Tasmanian studies, list published radiocarbon ages considered to be dependable, present new radiocarbon and thermoluminescence (TL) ages for 25 sites around Tasmania, and consider the evidence for the hypotheses that erosion processes at low and mid altitudes have been: (1) purely climatically controlled; and (2) influenced both by climatic and anthropogenic (increased fire frequency) effects. A total of 94 dependable finite ages (calibrated for radiocarbon and ‘as measured’ for TL and optically stimulated luminescence (OSL) determinations) are listed for deposits comprising dunes, colluvium, alluvium and loess-like aeolian deposits. Two fall in the >100 ka period, 15 fall in the period 65–35 ka, and 77 fall in the period 35–0.3 ka. There was a sustained increase in erosion recorded in the period 35–15 ka, as reflected by a greater number of dated aeolian deposits during this period. We considered three possible biases that may have affected the age distribution obtained: the limitations of radiocarbon dating, sampling bias, and preservation bias. Sampling bias may have favoured more recent dune strata, but radiocarbon dating and preservation biases are unlikely to have significantly distorted the age distribution obtained. Long but intermittent aeolian deposition is recorded at two sites (Southwood B; c. 59–28 ka and Dunlin Dune; c. 29–14 ka) but there is no evidence of regional loess deposits such as found in New Zealand. The timing of increased erosion in Tasmania between 35 and 30 ka approximately coincides with the intermittent ten-fold increase of dust accumulation between 33 and 30 ka in the Antarctic Dome C ice core. The absence of widespread erosion before 35 ka, the abrupt increase of erosion around this time, the frequent association of erosion products with charcoal, the arrival of people in Tasmania at c. 40 cal ka, and the known use of fires by Aborigines to maintain areas of non-climax vegetation suggest that ecosystem disturbance by anthropogenic fires, in a drier climate than that presently prevailing, may have contributed to erosion in lowland and mid-altitude Tasmania after 35 ka. Thus the Tasmanian erosion record provides circumstantial support for the proposition that human dispersal in southeast Australia was accompanied by significant ecological change.

Last Interglacial Age for aeolian and marine deposits and the Nahoon fossil human footprints, Southeast Coast of South Africa

Three hominid footprints preserved as casts were found in 1964 in Pleistocene aeolianites of the Nahoon Formation near East London, South Africa. Dating of the footprint-bearing aeolianite proved a lengthy and problematic task. Previous age estimates included a radiocarbon age of 29,090 − 390 + 410 years BP [Deacon, H.J., 1966. The dating of the Nahoon footprints. South African Journal of Science 62, 111–113], an infrared stimulated luminescence (IRSL) age of 144 ± 4 ka, a thermoluminescence age of 236 ± 8 ka (TL) and a luminescence subtraction age based on the IRSL and TL estimates of 75 ± 9 ka [Vogel, J.C., Wintle, A.G., Woodborne, S.M., 1999. Luminescence dating of coastal sands: overcoming changes in environmental dose rate. Journal of Archaeological Science 26, 729–733]. Thus there was no consistency among the ages derived using different dating methods. Here we describe optically stimulated luminescence (OSL) dating of quartz grains from a new set of samples collected from the footprint-bearing aeolianite and from associated geological formations. We also re-assessed the dose rate parameters for the sample for which TL and IRSL ages were reported and analysed the OSL signal from this sample. The new OSL dating yielded a coherent series of ages consistent with the stratigraphy as well as global and local sea level history. The indicated footprint age of 124 ± 4 ka thus relates to an important period of modern human evolution.

Luminescence chronology of cave sediments at the Atapuerca paleoanthropological site, Spain

Ascertaining the timing of the peopling of Europe, after the first out-of-Africa demographic expansion at the end of the Pliocene, is of great interest to paleoanthropologists. One of the earliest direct evidences for fossil hominins in western Europe comes from an infilled karstic cave site called Gran Dolina at Atapuerca, in a stratum ∼1.5 m below the Brunhes–Matuyama (B–M) geomagnetic boundary (780 ka) within lithostratigraphic unit TD6. However, most of the meters of fossil- and tool-bearing strata at Gran Dolina have been difficult to date. Therefore, we applied both thermoluminescence (TL) and infrared-stimulated-luminescence (IRSL) multi-aliquot dating methods to fine-silt fractions from sediment samples within Gran Dolina and the nearby Galería cave site. We also applied these methods to samples from the present-day surface soils on the surrounding limestone hill slopes to test the luminescence-clock-zeroing-by-daylight assumption. Within the uppermost 4 m of the cave deposits at Gran Dolina, TL and paired TL and IRSL ages range stratigraphically from 198 ± 19 ka to 244 ± 26 ka. Throughout Gran Dolina, all luminescence results are stratigraphically self-consistent and, excepting results from two stratigraphic units, are consistent with prior ESR-U-series ages from progressively deeper strata. Thermoluminescence ages culminate at 960 ± 120 ka approximately 1 m below the 780 ka B–M boundary. At Galería, with one exception, TL and IRSL ages range stratigraphically downward from 185 ± 26 ka to 503 ± 95 ka at the base of the lowermost surface-inwash facies. These results indicate that TL and (sometimes) IRSL are useful dating tools for karstic inwash sediments older than ca. 100 ka, and that a more accurate chronostratigraphic correlation is now possible among the main Atapuerca sites (Gran Dolina, Galería, Sima de los Huesos). Furthermore, the oldest TL age of ca. 960 ka from Gran Dolina, consistent with biostratigraphic and paleomagnetic evidence, implies a probable numeric age of 900–950 ka for the oldest hominin remains (∼0.8 m below the TL sample). This age window suggests a correspondence to Marine Isotope Stage (MIS) 25, a relatively warm and humid interglaciation.

Development, composition and age of indurated sand layers in the Late Quaternary coastal deposits of northern Moreton Bay, Queensland

Indurated sand in the Late Quaternary coastal plain succession of northern Moreton Bay was examined in sand-mine pits, drillcores and the eroded bank of an estuarine channel. Samples show that the cements usually coat grains and partially infill interstitial pores. Distinctive cement habits reflect different constituents that are dominantly kaolinite and amorphous organic-rich complexes. Trace-metal concentrations in the cements are lower than previously reported for soils and estuarine sediments in the study region. Optically stimulated luminescence and thermoluminescence ages of these deposits indicate that pedogenic induration occurs over long periods, up to approximately 90 000 years, with only incipient induration evident in deposits 16 000 – 2600 years old. However, the rate of induration is far higher in relatively coarse channel fill, in which mineral and amorphous organic-rich cements have precipitated from shallow groundwater that flowed laterally through the deposit. The degree of induration, therefore, is strongly influenced by the original depositional texture and morphology of deposits, with well-indurated gravely channel fill (76 700 ± 6500 y), at least 2 m thick, sitting adjacent to medium-grained sand probably of dune origin, which contains a 30 cm-thick induration horizon (98 000 ± 9900 y).

Thermoluminescence Dating of Late Pleistocene Sediments, St. Lawrence Lowland, Québec

This paper presents the results of a thermoluminescence (TL) dating program applied to waterlaid sediments of Late Pleistocene age, collected in the central St. Lawrence Lowland, in eastern Canada. The apparent TL ages were obtained using a partial bleach method (R-Gamma) in which the TL from light-sensitive traps is separated from the total TL. Fluvial (modern), marine (late-glacial) lacustrine (interstadial) and glacio-lacustrine (stadial) sediments yielded apparent ages ranging from 4 to 135 ka, and in general, these ages agreed with available stratigraphic evidence. Whilst testing the zeroing assumption, apparent TL ages obtained from modern fluvial and late glacial sediments suggest that laboratory overbleaching or insufficient natural bleaching may result in over-estimation of the apparent TL ages by 4-5 ka. All samples display anomalous fading, a problem that can be overcome by introducing a three month delay between artificial irradiation and glowing. Future research should focus on sediments for which the age as well as the sedimentology are well documented, such as the late glacial Champlain Sea sediments.

A ‘snapshot’ of the evolution of the Uruguay River (Del Plata Basin): the Salto depositional sequence (Pleistocene, Uruguay, South America)

This paper provides sedimentological details of the Salto depositional sequence of western Uruguay, which includes the Salto and the Bellaco Formations. These units are interpreted as evidence, in the Uruguayan landscape, of a Pleistocene forebear of the Uruguay River. The Salto depositional sequence, encompasses two depositional cycles: (a) the lower cycle, represented only by the Salto Formation, with conglomeratic sandstones and sandstones intercalated with pelites and fine sandstones; and (b) the upper cycle, represented by the Salto Formation and the Bellaco Formation, characterized by conglomerates and conglomeratic sandstones with horizontal stratification, discontinuous silicified sandy levels and gypsum–clay bodies. The Salto sequence is characterized by braided river deposits, genetically associated with lacustrine or palustrine and possible aeolian sediments. Cyclic alternations of channelized tractive currents and interchannel contexts are indicated. A possible Pleistocene age for the Salto Formation is discussed, in the light of new and preliminary information (thermoluminescence ages) from the lower cycle. There are several lines of evidence indicating semi-arid conditions during the ‘Salto event’. Comments on regional correlation are provided, as well as the effects of neotectonic processes.

Optically stimulated luminescence dating of heated materials using single-aliquot regenerative-dose procedure: a feasibility study using archaeological artefacts from India

Optically stimulated luminescence (OSL) dating of heated/fired materials of archaeological importance from various parts of India was attempted. A single-aliquot regenerative-dose (SAR) procedure was used for palaeodose determination in the quartz grains extracted from the heated materials using the luminescence produced by blue light stimulation. In most pottery samples, the palaeodose obtained using SAR-OSL is ∼6% lower than the palaeodose measured using thermoluminescence (TL) method. Broadly, there is good agreement between the SAR-OSL and TL ages of the artefacts and their archaeologically expected ages. The results suggest that routine dating of heated/fired materials using the SAR-OSL procedure is more practicable, especially when the TL sensitivity of the quartz grains is poor and availability of datable material is limited.

Active Tectonics of the Longmen Shan Region on the Eastern Margin of the Tibetan Plateau

Abstract: There is a massive amount of geomorphic evidence for active tectonics in the Longmen Shan at the eastern margin of the Tibetan plateau. We have surveyed some typical geomorphic markers including the Wenchuan‐Maowen, Beichuan‐Yingxiu and Pengxian‐Guanxian faults, terrace offsets, scarps, fault‐controlled saddles, dextral shutter ridges, dextral channel offsets, graben, shatter belts, and pull‐apart basins. Electron spin resonance (ESR) and thermoluminescence(TL) ages were obtained using silty sand taken from below the surface of the sediments. According to these data, we calculated the rates of thrusting and strike‐slip, and the results indicate that Cenozoic tectonic shortening at the plateau margin is minor with the rate of thrusting less than 1.10 mm/a and the rate of strike‐slipping less than 1.46 mm/a. The Longmen Shan is a zone of NNE‐trending dextral shear with slip‐dip ratio of 6:1‐1.3:1. From NW to SE, the thrust component becomes smaller, whereas the strike‐slip component becomes larger.

Baota landslide in the Three Gorges area and its OSL dating

Large old landslides are common in the Three Gorges area. Baota landslide, a large rockslide, is one of the largest landslides in the Three Gorges area. In the landslide body there are two terraces to be recognized. The two terrace deposits is not a two-grade terrace, but mainly remnants left by an occurrence of Baota landslide. Optically stimulated luminescence (OSL) dating suggests that the age of the terrace deposits is 38–32 kyr BP. The OSL ages along with other Thermoluminescence (TL) and Radiocarbon (14C) ages support the conclusion that the Baota landslide was originally triggered by strong precipitation occurred in a warm climate period of 30,000–40,000 years BP.

Luminescence dating of mid- to Late Wisconsinan aeolian sand as a constraint on the last advance of the Laurentide Ice Sheet across the Tuktoyaktuk Coastlands, western Arctic Canada

Luminescence dating of pre-glacial sand in the Tuktoyaktuk Coastlands, Northwest Territories, discounts an Early Wisconsinan age for the last Laurentide glaciation to cross the Arctic Coastal Plain and supports a Late Wisconsinan age. Aeolian dune sand from the Kittigazuit Formation near Cliff Point, on the southern shore of Liverpool Bay, predates till deposited during the Toker Point Stade. Potassium-rich feldspar from three stratigraphic sections ~35 km up-ice from the Toker Point glacial limit provides thermoluminescence age estimates that range from 18.7 ± 2.0 to 9.1 ± 1.0 ka and infrared stimulated luminescence age estimates of 23.8 ± 5.1 to 11.0 ± 2.1 ka. Quartz from four of the same samples provides optically stimulated luminescence age estimates of 16.5 ± 1.0 to 13.7 ± 0.9 ka. Collectively, these estimates reject the Early Wisconsinan age for the Toker Point Stade glaciation inferred hitherto from radiocarbon dating. A review of pre-glacial and post-glacial age estimates from the region indicates that during the Toker Point Stade ice advanced across the Tuktoyaktuk Coastlands no earlier than ~30 ka, and probably not before ~22 ka. Deglaciation had certainly commenced by 14.3 ka, and probably by ~16 ka. The Toker Point glaciation, therefore, dates approximately to the last glacial maximum, reinforcing the interpretation of the late rebuild up of the Laurentide Ice Sheet that characterized many parts of its margin.

下北半島，むつ燧岳火山地域の変質帯と変質岩の熱ルミネッセンス年代

Mutsu-Hiuchidake Volcano has an erosion caldera which shows a horseshoe-like geomorphological feature toward east. Tertiary strata as a basement are distributed in the caldera. Tertialy strata and a part of pyroclastic deposits of the Mutsu-Hiuchidake Volcano have altered strongly to moderately by hydrothermal activities related to the volcanism. This study is to clarify a progress history of the alteration by using a geological mapping, thermoluminescence (TL) dating, x-ray diffraction analysis, an infrared reflection absorption analysis and a fluid inclusion study. Highly altered zone is recognized in the area of midstream to upstream along the Ohakagawa and the Koakagawa within erosion caldera. The argillic alteration zone surround a silicification zone in the highly altered area shows a circular distribution. The strongly altered areas are along NNW-SSE to NNE-SSW fractures. The alteration areas were divided into the smectite, kaolinite, alunite and pyrophyllite zones. The kaolinite and alunite zones give the TL ages of quartz 67 ± 13 ka (KG-5), 88 ± 18 ka (OG-4) and 91 ± 23 ka (OG-1). The smectite zone within the argillic alteration zone of outside of collapse caldera, yield the ages 752 ± 215 ka (SO-2) and 615 ± 197 ka (KG-1). These TL ages suggest the hydrothermal activity end at 70 to 90 ka. The existence of pyrophyllite suggests that hydrothermal temperatures were 200 to 250 °C in these area. This is supported from the homogenization temperatures of fluid inclusions in calcite, 242 °C in average.

Geological and geochemical data from the proposed Sirente crater field: New age dating and evidence for heating of target

The proposed Sirente crater field consists of a slightly oblong main structure (main crater) 120 m in width and about 30 smaller structures (satellite craters), all in unconsolidated but stiff carbonate mud. Here we focus on the subsurface structure of the satellite craters and compare the Sirente field with known meteorite crater fields. We present a more complete outline of the crater field than previously reported, information on the subsurface morphology of a satellite crater (C8) 8 m in width, radiocarbon and thermoluminescence (TL) ages of material from this crater, and evidence for heated material in both crater C8 and the rim of the main crater. Crater C8 has a funnel shape terminating downwards, and evidence for soil injection from the surface to a depth of 9 m. The infill contained dispersed charcoal and small, irregular, porous fragments of heated clay with a calibrated age of B.P. 1712 (13C-corrected radiocarbon age: B.P. 1800+/-100) and a TL age of B.P. 1825 (calculated error +/-274). Together with previous radiocarbon age (B.P. 1538) of the formation of the main crater (i.e., target surface below rim), a formation is suggested at the beginning of the first millennium A.D. Although projectile vaporization is not expected in Sirente-sized craters in this type of target material, we used geochemistry in an attempt to detect a meteoritic component. The results gave no unequivocal evidence of meteoritic material. Nevertheless, the outline of the crater field, evidence of heated material within the craters, and subsurface structure are comparable with known meteorite crater fields.

An optical age chronology of late Quaternary extreme fluvial events recorded in Ugandan dambo soils

There is little geochonological data on sedimentation in dambos (seasonally saturated, channel-less valley floors) found throughout Central and Southern Africa. Radiocarbon dating is problematic for dambos due to (i) oxidation of organic materials during dry seasons; and (ii) the potential for contemporary biological contamination of near-surface sediments. However, for luminescence dating the equatorial site and semi-arid climate facilitate grain bleaching, while the gentle terrain ensures shallow water columns, low turbidity, and relatively long surface exposures for transported grains prior to deposition and burial. For this study, we focused on dating sandy strata (indicative of high-energy fluvial events) at various positions and depths within a second-order dambo in central Uganda. Blue-light quartz optically stimulated luminescences (OSL) ages were compared with infrared stimulated luminescence (IRSL) and thermoluminescence (TL) ages from finer grains in the same sample. A total of 8 samples were dated, with 6 intervals obtained at ∼35, 33, 16, 10.4, 8.4, and 5.9 ka. In general, luminescence ages were stratigraphically, geomorphically and ordinally consistent and most blue-light OSL ages could be correlated with well-dated climatic events registered either in Greenland ice cores or Lake Victoria sediments. Based upon OSL age correlations, we theorize that extreme fluvial dambo events occur primarily during relatively wet periods, often preceding humid-to-arid transitions. The optical ages reported in this study provide the first detailed chronology of dambo sedimentation, and we anticipate that further dambo work could provide a wealth of information on the paleohydrology of Central and Southern Africa.

Luminescence dating at the archaeological and human burial site at Roonka, South Australia

Roonka, the Aboriginal habitation and burial site on the River Murray, South Australia, was excavated from 1968 to 1983. In 1983, thermoluminescence (TL) ages were obtained for several fireplaces at the East Bank site. Sandy dune sediments collected from East Bank were also analysed using traditional TL methods and ages were found at depths down to the base at 2.6 m. Now, 20 years on, with optical dating methods well established, it seemed instructive to repeat the measurements using new techniques, specifically the single aliquot regeneration dose protocol. This has provided confirmation of the TL ages and provided an age framework for both the archaeological and geological aspects of Roonka. The ages confirm the archaeological description of the structure of the dune and show that only the top 20% is the Holocene Bunyip formation. The lower part is assigned to the Woorinen Formation, formed during and after the last glacial maximum. Burials at East Bank took place between about 16 and 20 ka, substantially earlier than those on the Roonka Flat, but consistent with the earliest evidence of occupation on the Flat. They are one of the very few securely dated Pleistocene burials in Australia. Whether the individuals were gracile or robust is not known.

Thermoluminescence dating of the ancient Chinese porcelain using a regression method of saturation exponential in pre-dose technique

This paper studies the thermoluminescence (TL) dating of the ancient porcelain using a regression method of saturation exponential in the pre-dose technique. The experimental results show that the measured errors are 15% (±1s) for the paleodose and 17% (±1s) for the annual dose respectively, and the TL age error is 23% (±1s) in this method. The larger Chinese porcelains from the museum and the nation-wide collectors have been dated by this method. The results show that the certainty about the authenticity testing is larger than 95%, and the measurable porcelains make up about 95% of the porcelain dated. It is very successful in discrimination for the imitations of ancient Chinese porcelains. This paper describes the measured principle and method for the paleodose of porcelains. The TL ages are dated by this method for the 39 shards and porcelains from past dynasties of China and the detailed data in the measurement are reported.

鬼首・鳴子カルデラ周辺の後期更新世火砕流堆積物及び火山岩の熱ルミネッセンス年代

Thermoluminescence (TL) dating of volcanic rocks and pumice flows around Onikobe-Naruko area was carried out by checking suitability of the sample for this technique. Samples for TL dating were divided into three ranks, A, B and C, on the basis of physical/petrographical characters and geological origin. Rank A sample is hard and compact rock which is chemically stable. Rank B is soft pumice flow or equivalent sample which is chemically unstable for long geologic time. Rank C is sediment deposited in water. For precise and reliable TL dating, only rank A sample must be used. TL ages obtained from samples of rank A are 30.4 ka for Naruko dome lava, 187 ka for Takahinatayama lava, 169 ka and 170 ka for Shimoyamazato Tuff Formation, and 296 ka and 268 ka for Ikezuki Tuff Formation. Mitsuzawa Formation at western part of Naruko, pyroclastic flows at Yubama and Byobuiwa are identified as Ikezuki Tuff Formation due to their TL ages of 258 ka, 231 ka to 345 ka and 238 ka, respectively. TL ages of two sites are not well coincide to Ikezuki Tuff Formation. TL ages of the samples from Yubama Onsen and Gyojadaki are 169 ka and 362 ka, which correspond to the age of other eruption products rather than Ikezuki Tuff Formation. TL age data for 83 samples of rank B and C are checked by comparison with those of rank A and existence age data. It could be reconciled with stratigraphic evidence and corresponding ages of rank A. Rank B and C data are selectively apply for preliminary stage or special purposes that the rough ages are still useful for research program.