Late Quaternary lake level record of Orog Nuur,southern Mongolia,revealed by optical dating of paleo-shorelines

The Late Quaternary hydroclimatic evolution of lake systems in Mongolia remains unclear. Here we present a record of lake level variations at Orog Nuur in the Valley of Gobi Lakes in southern Mongolia, since the last interglaciation, based on paleo-shoreline dating using quartz optically stimulated luminescence (OSL) and K-feldspar post-infrared infrared stimulated luminescence (pIRIR) signals. Due to feldspar contamination that could not be eliminated, the OSL signals of quartz single-aliquots (SA), except for two Holocene samples, were unsuitable for dating and a double SA regenerative-dose (SAR) protocol was used for the quartz fraction of these two samples. The pIR₅₀IR₁₇₀ and pIR₂₀₀IR₂₉₀ signals of K-feldspar SA were used to date Holocene samples and old samples (>100 ka), respectively, with the SAR protocol. To determine the bleaching condition of the pIR₂₀₀IR₂₉₀ signals, the first pIRIR dating of K-feldspar single-grains of lake shoreline sediments in Mongolia was performed. The equivalent doses of K-feldspar grains show normal distributions, suggesting that the pIR₂₀₀IR₂₉₀ signals are well-bleached. Overall, the results, combined with those of previous studies, show that a mega-lake developed at 56 m above the modern lake level (a.m.l.) during MIS 5e (124.2 ± 6.8–114.7 ± 8.0 ka). Holocene high-stands occurred in the last deglaciation–early Holocene (11.1 ± 1.0 ka) at 23 m a.m.l. and in the mid-Holocene (6.7 ± 0.8–3.3 ± 0.4 ka) at 20–14 m a.m.l. The dimensions of the paleo-lakes were recovered, and a hydrological index indicates that the effective moisture during MIS 5e and the mid-Holocene was 10.7 times and 3.6–5.0 times larger than today, respectively. Finally, the possible mechanisms behind the lake level history are discussed based on correlation with independent paleoclimatic records.     

Chronostratigraphy of a sediment record from the Hajar mountain range in north Oman: Implications for optical dating of insufficiently bleached sediments

In this study we report on optical stimulated luminescence (OSL) ages of quartz extracted from a sedimentary record in the N-Oman mountain range. Equivalent dose (D_E) distributions derived from single aliquot measurements (SAR) of small aliquots (ca. 200 grains) were investigated to test whether the skewness and broadness of the dose distribution can be used as criteria for the identification of insufficient bleaching. Furthermore, the methods proposed by Lepper and McKeever [2002 An objective methodology for dose distribution analysis. Radiation Protection Dosimetry 101 (1–4), 349-352]. Singhvi [Juyal, N., Chamyal, L.S., Bhandari, S., Bushan, R., Singhvi, A.K., in press. Continental record of the southwest monsoon during the last 130 ka: evidence from the southern margin of the Thar Desert, India. Quaternary Science Review] and Fuchs and Lang [2001 Fuchs, M., Lang, A., 2001. OSL dating of coarse-grain fluvial quartz using single-aliquot protocols on sediments from NE Peloponnese, Greece. Quaternary Science Review 20, 783–787.] to derive D_E's from insufficiently bleached sediments were compared. At first, the investigations were carried out on artificially bleached, irradiated and mixed quartz material from the Oman study area to simulate insufficiently bleached sediments. Then, the various statistical methods for identifying insufficient bleaching and D_E derivation were applied to the natural samples from the study area, where 18 samples were measured. For the identification of insufficient bleaching the preferential parameter is the broadness of a distribution. For D_E calculation, both the Singhvi method and the Fuchs and Lang method produce similar results, which are consistent with the stratigraphic order. A drawback of both methods is their sensitivity to low outliers. The Lepper and McKeever method was not applied to the natural samples, due to limitations in its application to a small number of aliquots and due to the ambiguous identification of the rising limb of the dose distributions.     

ESR dating of glacial moraine deposits: Some insights about the resetting of the germanium (Ge) signal measured in quartz

The electron spin resonance (ESR) dating of tills using germanium-doped (Ge) paramagnetic centers in quartz has advantages over other dating techniques, as quartz is common, processing is easy, and the technique has the potential for dating features several hundreds of thousands years old. ESR dating of moraines is based on the supposition that either subglacial comminution or exposure to sunlight resets the signal. However, actual dating suggests that a signal that is initially present cannot be bleached to zero by grinding alone. We found that grinding coarse samples (0.5–1 mm in diameter) to the mean grain size of fine sand (0.125–0.193 mm) reduced the signal intensity to 53–69% of its original value. From the value of the signal difference, one can devise a correction factor for ESR ages of subglacial sediment. Polymineralic grains are commonly present in till. Exposure of them to sunlight for several days can reduce the signal intensity to 7–8% of its original value within 1–2 mm thick of the sediment surface. However, within 5–8 mm of the sediment surface, exposure to sunlight for over one week only reduced the signal intensity to mean plateau values of 42–50% of the initial value. Mixing upper and lower layers of the samples during exposure to sunlight changed the signal intensity. This suggests that the amount of bleaching varies spatially. Sediments initially deposited at the margins of ice caps or ice sheets and subsequently overridden may have been sufficiently exposed to sunlight to allow ESR dating of moraines. The purity of the quartz and the grain size have significant impacts on signal intensity; intensive purification and the use of a uniform fine sand fraction are thus recommended.     

Single grain optical dating of glacigenic deposits

Determining the age of glacigenic sediments is difficult for many geochronological methods because of the lack of suitable materials for analysis. Luminescence dating can be applied to the mineral grains making up the glacigenic sediments. However a major source of uncertainty in previous studies has been whether the mineral grains were exposed to sufficient daylight prior to deposition for the luminescence signal to be reset. Measurements of the optically stimulated luminescence signal from single sand-sized quartz grains offers the potential for explicitly identifying if a sediment contains grains that were not exposed to sufficient daylight to reset their signal. Statistical analysis of the resulting data can then reject those grains to allow the age of the sample to be determined. This study is the first to apply single grain optical dating to glacigenic sediments, and demonstrates the issues involved by analysis of samples from Chile and Scotland. Ages from 2.4±0.5 to 17.3±1.5 ka are produced. Comparison of the results with independent age control suggests that the ages are reliable. The results also show that the extent of bleaching at deposition varies considerably from one sample to another. For the most incompletely bleached sample, luminescence measurements based on the average of many hundreds or thousands of grains would have overestimated the age of the sample by 60 ka, but the single grain method proposed here was able to reliably date it.     

ESR dating of fluvial quartz: Estimate of the minimal distance transport required for getting a maximum optical bleaching

An ESR experimental study of artificial optical bleaching of sedimentary quartz has shown that the aluminum center was maximally bleached after a 6-month illumination equivalent to natural light. This duration seems too long to apply in natural conditions. Nevertheless, the measurement of the ESR intensity of aluminum centers in quartz extracted from modern sediments and deposited in sandy bars shows that the maximum bleaching has effectively been reached.

In order to determine the relationship between the bleaching and the distance covered by a quartz grain in a river, samples were collected along the Creuse River (France) from its spring to about 170 km downstream, where maximum bleaching levels were observed in previous studies. The ESR intensities of the aluminum and titanium centers in quartz were measured, using X-band spectroscopy, before and after artificial bleaching. The difference measured between these sub-samples shows that the maximum bleaching level is obtained in the course of the first kilometer. Hence, the assumption that ESR dating of fluvial sediment is based on the optical bleaching was validated.     

OSL dating of sediments from deserts in northern China

Aeolian samples from deserts in northern China were studied using the optically stimulated luminescence (OSL) of quartz and potassium (K) feldspar separates. K-feldspar has shown advantages over quartz for dating samples younger than 100 years, due to its more homogeneous equivalent dose (D_e) values, higher internal dose rate and higher luminescence sensitivity to dose. Without additional measurements, the luminescence characteristics of quartz obtained in D_e determination procedures can be used to reveal the source material and/or quartz thermal history for the deserts in northern China. The results indicated that the duration of paleosol formation in desert areas reflects regional paleoenvironments.     

Progress in optical dating of guano-rich sediments associated with the Deep Skull, West Mouth of the Great Cave of Niah, Sarawak, Borneo

The West Mouth of the Great Cave of Niah is one of the major archaeological sites in Southeast Asia; the radiocarbon chronology of this site currently places the earliest presence of Homo sapiens (a Deep Skull find) in Southeast Asia at about 45 ka BP. An optical dating programme using sand-sized quartz was initiated in the West Mouth to complement the radiocarbon chronology. This paper reports on the progress in dating a key sample (sample 376r) that was taken from deposits containing the Deep Skull. A somewhat novel procedure was developed to separate and clean quartz grains from the unusual guano-rich deposits. From this, only a small quantity of quartz grains could be recovered and 36 aliquots (1 mm in diameter) were prepared, each consisting of 80 grains. This sample was dated by means of the single-aliquot regenerative-dose (SAR) method using the protocols of Murray and Wintle [2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73], and of Choi et al. [2003. Luminescence dating of well-sorted marine terrace sediments on the southeastern coast of Korea. Quaternary Science Reviews 22, 407–421]. The results showed a wide distribution of equivalent doses; this distribution is inferred to be due to bioturbation, variable bleaching at deposition, and to local variations in the dose rate within the sample site. Dose rates were measured using both field (in-situ γ-ray spectrometry, IGRS) and laboratory (inductively coupled plasma mass spectrometry/atomic emission spectrometry, ICP-MS/AES; and isotope dilution, ID) methods. There was significant disagreement between the concentrations of radioisotopes found using laboratory and field measurements, indicating sediment heterogeneity and also possible disequilibrium in the ²³⁸U decay chain. Future work in the West Mouth should therefore concentrate on taking sediment samples of at least 500–600 cm³, improving the dose rate estimates (e.g. by high-resolution γ-ray spectrometry) and investigating other luminescence signals (e.g. red thermoluminescence) as potential geochronometers.     

Optical dating of sediments in Wadi Sabra (SW Jordan)

At Wadi Sabra (SW Jordan) human occupation dates back to the Palaeolithic and Epipalaeolithic. Although there is stratigraphic correlation based on archaeological finds of Ahmarian origin, numerical age estimates are lacking. We applied single-aliquot optical dating of coarse grained quartz of wadi deposits and investigated the luminescence properties in detail to achieve more accurate age information about the time of human occupation. Weak luminescence signals and scattered dose distributions characterise the multi-grain aliquots. The residual doses of the investigated modern wadi sediment are between 0 and 7 Gy. Moreover, comparison of equivalent dose (De) values of 1 mm and 8 mm aliquots shows higher equivalent doses for the large aliquots. Both experiments indicate that the luminescence signal is partially bleached prior to deposition. The dose distributions of all samples are broadly scattered and have overdispersion values between 25 and 43%, some samples are significantly skewed. The shape of the dose distributions points to other sources of scatter, in addition to partial bleaching. Comparison of 1 mm multi-grain and single-grain data demonstrates that the luminescence signal of one multi-grain aliquot most likely is from a single grain. For this reason, variation in the number of photon counts due to the weak luminescence intensity and variations in beta microdosimetry have a bigger impact on the spread of dose distributions. However, we cannot quantify the particular impact of partial bleaching, weak luminescence intensity and beta microdosimetry. To account for the spread of the dose distribution, we use the central age model to calculate equivalent doses. Age calculations yield results in the range of 30–48 ka.     

Methodological studies on luminescence dating of volcanic ashes

We report here the results of a feasibility study of luminescence dating of polymineralic volcanic ash. Of the several possible protocols that used different emission bands and different IR stimulation regimes, the post infrared-infrared stimulated luminescence (pIR-IRSL) signal (detected using a violet-blue emission window with stimulation temperature in the region 260–320 °C) provided the most stable signal. This involved, i) identification of the most suitable temperature for pIR-IRSL read out, ii) determination of alpha efficiency and, iii) estimation of anomalous (athermal) fading rate. Anomalous fading rate (g-value in %/decade) of pIR-IRSL signal at 300 °C was 0.0–1.6%/decade and it ranged from 2.4 to 5.2%/decade for IRSL at 50 °C, both preheated to 320 °C. Thus, though more stable, pIR-IRSL signals may fade in nature, and even during laboratory extended irradiation. Of the models for fading correction by Huntley and Lamothe (2001) and Kars et al. (2008), the Kars et al. (2008) model performed better as the natural luminescence intensity was closer to the onset of saturation in the luminescence dose response curve. Our measurements suggest that alpha efficiencies of the pIR-IRSL signals are higher than that of IRSL. Fading corrected pIR-IRSL single aliquot regeneration (SAR) protocol based ages on three of the five volcanic ash beds are in agreement with the expected ages of ∼74 ka, based on geochemical association of the present samples to be the Youngest Toba Tuff (YTT). Other ash samples that gave ages of <24 ka and <37 ka, were inferred to have been in their secondary context, reworked from their original depositional sites. The onset of saturation dose of the pIR-IRSL signal (D₀) was ∼330 Gy and this implied a maximum measurable equivalent dose of 660 Gy. The minimum detectable dose was ∼5 Gy. These dose limits correspond to a typical age range of 1–150 ka using the pIR-IRSL signal for volcanic ashes.     

地震波双向照明的概念及计算方法

根据WRW模型理论,从地震波传播的物理过程给出了双向照明的具体概念,基于该概念提出了计算地震波双向照明强度的基本思路(称为DUC双向照明方法).为了有效提高DUC双向照明方法的计算效率,又提出了DUC-DC双向照明方法,并将提出的上述方法与传统的双向照明计算方法从计算精度和计算效率等方面进行了对比.试验结果表明,本文提出的双程波DUC方法得到的双向照明结果与理论照明结果完全一致,从而证明了本文提出的双向照明概念的正确性.而单程波DUC-DC计算方法大幅度提高了双向照明强度的计算效率.本文提出的双向照明计算方法不仅能考虑到检波器接收孔径问题,还能将地表不同位置检波器处接收能量不同这一因素纳入考虑范围.     

Optical dating of Holocene sand dune activities in the Horqin sand-fields in inner Mongolia, China, using the SAR protocol

The Horqin sand-field in northeastern Inner Mongolia, China, had been the fertile grassland in North China, but desertification and sand-dust storm have increasingly occurred in the past decades [Zhu and Wang, 1992. Theory and practice of sandy desertification in China (in Chinese with English abstract). Quaternary Sciences 2, 97]. To understand the Holocene sand dune activities in this region, five sand dune profiles were investigated, and 32 coarse grain quartz samples were dated by OSL using the single-aliquot regenerative-dose (SAR) protocol [Murray and Wintle, 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73]. For cross-checking, six organic-rich samples from the paleosols and sandy peat/mud were dated by both ¹⁴C and quartz OSL. With one exception, ¹⁴C and quartz OSL dating results show good agreements. Based on the consistent results of five sand dune profiles, a chronology of Holocene dune activity in Horqin sand-field is established as follows: (i) active sand dunes built up widely before 10 ka; (ii) dunes semi-stabilized between 10 and 7.5 ka ago; (iii) the dunes solidify and chernozem soils developed between 7.5 and 2.0 ka ago; and (iv) partially re-mobilization of dunes occurred since about 2.0 ka ago.     

地震照明分析及其在地震采集设计中的应用

地震照明分析是在给定地下背景结构的情况下用模拟方法研究采集系统对地下结构的探测能力.对目标照明的影响主要来自观测系统的设置,上覆地质结构的复杂性以及目标倾角等三项因素.我们将上述因素的影响统一纳入到对照明的定量计算中.本文阐述了关于地震照明的一系列基本概念,并基于波动理论给出对不同类型照明的计算方法.首先将入射和散射波分解到局部角度域并导出局部照明矩阵,它包括了在目标附近所有可能的入射和散射方向对照明的贡献.从照明矩阵出发,研究入射和反射波在角度域中与反射面的相互作用,并由此获得对地下结构的不同照明描述.作为例子,具体给出了对局部照明矩阵,空间体照明,反射面定向照明,反射面照明角度覆盖,以及对反射面可视性的计算方法,并给出了相应的数值计算结果. 最后,讨论了照明分析方法在地震采集设计中的一些可能应用.     

A Bayesian hierarchical age model for optical dating of single grains of quartz

In optical dating, the last time that a sample of sediment was exposed to sunlight is determined by dividing its equivalent dose (D_e) by the dose rate. For single-grain dating, the sample D_e is based on the statistical analysis of the distribution of D_e values estimated for individual grains, whereas the dose rate is usually determined from measurements of the environmental radioactivity of the bulk sample, together with allowances for radiation sources internal to the grains and cosmic rays. Conventionally, the D_e and dose rate are measured and analysed separately to produce an estimate of the depositional age of a sample, but this approach may result in loss of information because distributions of single-grain D_e values are influenced by several factors. Existing statistical models do not incorporate all the key information contributing to age estimation, such as the pattern and scale of dispersion of single-grain D_e values and dose rates, the associated measurement uncertainties, the effect of natural variability among grains, and the outlier probabilities of D_e and dose rate estimates. Here we propose an empirical Bayesian hierarchical age model (BHAM) for optical dating of quartz samples that incorporates the above information to estimate their depositional ages. The BHAM is based on the implementation of standardised growth curve and L_nT_n methods to integrate information on the full distribution of single-grain D_e values, sources of measurement uncertainty, beta-dose heterogeneity (observed or modelled), and detection of outliers. We present the results of validation tests using data sets of optically stimulated luminescence measurements and dose rates obtained for quartz samples dated previously from Denisova Cave (Russia) and for simulated samples. We conclude that the BHAM represents a robust and flexible approach to dealing with data for single grains of quartz within a Bayesian hierarchical framework and is suitable for application to sediments deposited in a variety of depositional settings.     

地质定年方法综述与地球物理定年

年代确定在地学中得到广泛应用.而作为地史学中重要的组成部分，年代确定为地质时期中地球岩石圈在时间上发展和演变提供了重要的时间约束.本文综述了四种定年方法：即古生物法；古地磁法；同位素法和地球物理法.随着地球物理的探测技术的发展，地球内部精细结构得到揭示.我们认为，应用地球物理资料确定年龄将可以弥补其它方法的缺陷，可能为地球内部三维岩石定年提供支撑.     

A revised burial dose estimation procedure for optical dating of youngand modern-age sediments

The presence of genuinely zero-age or near-zero-age grains in modern-age and very young samples poses a problem for many existing burial dose estimation procedures used in optical (optically stimulated luminescence, OSL) dating. This difficulty currently necessitates consideration of relatively simplistic and statistically inferior age models. In this study, we investigate the potential for using modified versions of the statistical age models of Galbraith et al. [Galbraith, R.F., Roberts, R.G., Laslett, G.M., Yoshida, H., Olley, J.M., 1999. Optical dating of single and multiple grains of quartz from Jinmium rock shelter, northern Australia: Part I, experimental design and statistical models. Archaeometry 41, 339–364.] to provide reliable equivalent dose (D_e) estimates for young and modern-age samples that display negative, zero or near-zero D_e estimates. For this purpose, we have revised the original versions of the central and minimum age models, which are based on log-transformed D_e values, so that they can be applied to un-logged D_e estimates and their associated absolute standard errors. The suitability of these ‘un-logged’ age models is tested using a series of known-age fluvial samples deposited within two arroyo systems from the American Southwest. The un-logged age models provide accurate burial doses and final OSL ages for roughly three-quarters of the total number of samples considered in this study. Sensitivity tests reveal that the un-logged versions of the central and minimum age models are capable of producing accurate burial dose estimates for modern-age and very young (<350 yr) fluvial samples that contain (i) more than 20% of well-bleached grains in their D_e distributions, or (ii) smaller sub-populations of well-bleached grains for which the D_e values are known with high precision. Our results indicate that the original (log-transformed) versions of the central and minimum age models are still preferable for most routine dating applications, since these age models are better suited to the statistical properties of typical single-grain and multi-grain single-aliquot D_e datasets. However, the unique error properties of modern-age samples, combined with the problems of calculating natural logarithms of negative or zero-Gy D_e values, mean that the un-logged versions of the central and minimum age models currently offer the most suitable means of deriving accurate burial dose estimates for very young and modern-age samples.     

Chronology of an oyster reef on the coast of Bohai Bay, China: Constraints from optical dating using different luminescence signals from fine quartz and polymineral fine grains of coastal sediments

Fossil oyster reefs are indicators of past sea levels, and their formation is usually dated by means of radiocarbon. However, radiocarbon dating of the shells from coastal areas may be complicated by the varying sources of carbon. Here we applied optical dating methods to date the samples from above and below a fossil oyster bed in a section on the coast of Bohai Bay, China. The optical ages of the sediments were used to constrain the oyster bed. Single-aliquot regenerative-dose procedures using the OSL signal from fine grain quartz, the IRSL and post-IR OSL signals from polymineral fine grains were employed to determine equivalent dose (D_e). The behaviors of the different luminescence signals from quartz and polymineral grains during D_e measurements were examined. The results showed that the quartz OSL signal is more reliable than the polymineral IRSL and post-IR OSL signals with respect to dating for these coastal samples. The optical ages indicated that the oyster reef formed between ca. 6.2 and 5.0 ka.     

Segmentation of alluvial fans in death valley,california: New insights from surface exposure dating and laboratory modelling

Laboratory experiments, recent paleoenvironmental analyses of rock varnish, and surface exposure dating of geomorphic units have led to new insights into the process of entrenchment and segmentation of alluvial fans, and into the history of Quaternary sedimentation in Death Valley. Entrenchment begins at the fanhead. As the trench deepens, its down-slope end migrates down-fan, taking several tens of thousands of years to reach lower parts of the fan. Laboratory experiments suggest, however, that a new segment begins to grow at the toe long before the trench reaches this part of the fan. Furthermore, the initial slope of the segment is not the equilibrium slope. Field evidence supports this model. The tectonic tilting that caused entrenchment and segmentation in Death Valley may have been triggered by loading of the valley with water. Sedimentation on the salt pan in southern Death Valley is not, at present, in equilibrium with that on the fans. Rather, it seems to be adjusting to an increase in the amount of fine material reaching the playa, due in part to breaching of the outlet of Lake Tecopa somewhat after 600 ka BP, and in part to subsidence of different parts of the valley at different rates. Failure to recognize this disequilibrium resulted in errors in earlier estimates of the age of the segmentation events.     

Optical dating of aeolian and fluvial sediments in north Tian Shan range,China: Luminescence characteristics and methodological aspects

Loess and fluvial sand are important materials for dating river terraces and alluvial fans. This study focuses on the methodological aspects of dating loess and fluvial deposits from the northern flank of the Tian Shan range, China, using sand-sized quartz and potassium (K) feldspar. Luminescence characteristics of quartz and K-feldspar were studied for searching suitable dating procedures. Our results indicate that 1) most quartz aliquots were contaminated by feldspar, and were dated using a post-infrared optically stimulated luminescence (post-IR OSL) procedure. A Fast ratio acceptance threshold of 15 can be applied to select these aliquots with post-IR OSL signals dominated by quartz OSL; 2) the multi-elevated-temperature post-IR IR stimulated luminescence (MET-pIRIR) procedures are applicable for K-feldspar. A test dose of ∼30% of the natural dose is appropriate for dating of older (>10 ka) samples. An Age (T, t) plateau test can be used to evaluate the dating results; 3) for the loess samples, both quartz and K-feldspar were well bleached and are suitable for dating. Dating using K-feldspar is preferred for its higher efficiency; 4) for the fluvial sand samples, only the quartz grains were fully bleached. Single-aliquot dating of quartz gives reliable ages.     

地震照明叠前深度偏移方法综述

对地震照明叠前深度偏移的基本概念、实现方法进行了分类和阐述.地震照明叠前深度偏移是通过对震源和炮记录进行合理的选择和合成,从而进行地震照明成像的一种有效方法.其可以分为平面波偏移和小束波偏移.理论模型的处理效果证明地震照明叠前深度偏移成像技术有很高的计算效率,并且还可以提高地下特定目标的成像质量.     

Radiometric dating of Meipu hominin site in China by coupled ESR/U-series and cosmogenic 26Al/10Be burial dating methods

The Three Gorges and Western Hubei area in the geographic central part of China was a potential migration corridor for early hominin and mammals linking South and North China during the Pleistocene period. Some key early hominin sites are known in this region where limestone cave and fissure sites are numerous but difficult to date as beyond the dating range of OSL and mass spectrometry U-series method. Here, we report radiometric dating study for such a hominin site, Meipu (Hubei Province), by coupled ESR and U-series dating of nine fossil teeth and cosmogenic ²⁶Al/¹⁰Be burial dating of one quartz sediment. The burial age calculated by simple burial model (573 ± 266 ka) gives a minimum age constraint of the sediment. The fossil dating provided two main age groups at 541 ± 48 ka and 849 ± 39 ka, the older age group is in agreement with the U-series age (>630 ka) of the flowstone overlying the fossil layer and the paleomagnetic data which placed the Brunhes-Matuyama boundary in the fossil layer. The reason of this age difference is probably caused by the U-content discrepancy in the enamel of the dated fossil samples. This study exhibits the limitation of ESR/U-series fossil dating and the importance of using multiple dating approach when it is possible in order to identify the problematic ages.