K-feldspar IRSL dating of a Pleistocene river terrace staircase sequence of the Lower Tejo River (Portugal,western Iberia)

We present the results of K-feldspar IRSL dating of the four lower terraces (T3–T6) of the Portuguese Tejo River, in the Arripiado-Chamusca area. Terrace correlation was based upon: a) analysis of aerial photographs, geomorphological mapping and field topographic survey; b) sedimentology of the deposits; and c) luminescence dating. Sediment sampled for luminescence dating gave unusually high dose rates, of between 3.4 and 6.2 Gy/ka and, as a result, quartz OSL was often found to be in saturation. We therefore used the IRSL signal from K-feldspar as the principal luminescence technique. The K-feldspar age results support sometimes complex geomorphic correlations, as fluvial terraces have been vertically displaced by faults (known from previous studies). Integration of these new ages with those obtained previously in the more upstream reaches of the Tejo River in Portugal indicates that the corrected K-feldspar IRSL ages are stratigraphically and geomorphologically consistent over a distance of 120 km along the Tejo valley. However, we are sceptical of the accuracy of the K-feldspar ages of samples from the T3 and T4 terraces (with uncorrected D_e values >500 Gy). In these cases the Dose Rate Correction (DRC) model puts the natural signals close to luminescence saturation, giving a minimum corrected D_e of about 1000 Gy, and thus minimum terrace ages; this may even be true for those doses >200 Gy. Luminescence dating results suggest that: T3 is older than 300 ka, probably ca. 420–360 ka (～Marine Isotope Stage [MIS]11); T4 is ca. 340–150 ka (～MIS9-6); T5 is 136–75 ka (～MIS5); T6 is 60–30 ka (MIS3); an aeolian sand unit that blankets T6 and some of the older terraces is 30–≥12 ka. Collectively, the luminescence ages seem to indicate that regional river downcutting events may be coincident with periods of low sea level (associated, respectively, with the MIS10, MIS6, MIS4 and MIS2).     

Maximum age limitation in luminescence dating of Chinese loess using the multiple-aliquot MET-pIRIR signals from K-feldspar

Numerical dating of loess is important for Quaternary studies. Recent progress in post-infrared infrared-stimulated luminescence (pIRIR) signals from potassium-rich feldspar has allowed successful dating of Chinese loess beyond the conventional dating limit based on quartz optically stimulated luminescence (OSL) signals. In this study we tested the multiple-aliquot regenerative-dose (MAR) pre-dose multiple-elevated-temperature post-IR IRSL (pMET-pIRIR) procedure on samples from the palaeosol S5 (∼480 ka) and S8 (∼780 ka) layers from the Luochuan and Jingbian sections, respectively. The results show that (1) compared to sensitivity-corrected signal (L_x/T_x), a higher saturation dose is observed for the sensitivity-uncorrected MET-pIRIR signals (L_x), suggesting that MAR is advantageous for dating old samples; (2) negligible fading component can be achieved using the pMET-pIRIR procedure; (3) for the sample from the top of palaeosol S5, D_e values (1360 + 226/-167 Gy) broadly consistent with expected D_e (1550 ± 72 Gy) can be obtained using the sensitivity-uncorrected 300 °C MET-pIRIR signal. Our study suggests that a D_e value of about 1800 Gy may be the maximum dating limit of Chinese loess using the MAR pMET-pIRIR procedure.     

High resolution OSL dating back to MIS 5e in the central Sea of Okhotsk

Marine sediments contain important archives of past ocean and climate changes, but at high latitudes the absence of carbonate has prevented the construction of accurate chronological models. We have begun a study to (1) determine the accuracy of luminescence ages in deep-sea marine sediments, e.g. by comparison with marine oxygen isotope stratigraphy where possible, (2) describe changes in sedimentation rate through time, and (3) test whether it is possible to date back to marine isotope stage 5e (MIS 5e). We show here that optical dating of fine grains of quartz from the central Sea of Okhotsk is able to provide an accurate and precise chronology for the reconstruction of the palaeoceanic and palaeoclimatic environment at our site. The upper 6.5 m of the 18.42 m long core MR0604-PC07A is believed, based on its magnetic susceptibility and the oxygen isotope (δ¹⁸O) records to contain the last ～150 ka. Forty OSL samples were taken from this upper part of the core. The single-aliquot regenerative-dose (SAR) procedure is used for equivalent dose (D_e) determination. The luminescence characteristics of fine-grained quartz (4–11 μm) extracted from the core are described. The OSL signal is dominated by the fast component and a dose recovery test shows that we can accurately measure a known dose given in the laboratory prior to any heat treatment. Dose rates were determined using high-resolution gamma spectrometry, and vary between 0.4 and 1.6 Gy/ka. The OSL ages from this section lie between ～140 ka and ～15 ka and are in very good agreement with the δ¹⁸O stratigraphy up to MIS 5e. A clear change in sedimentation rate is identified: between ～139 and 110 ka, the sedimentation rate was ～0.09 m/ka, but then from ～110 to 15 ka, the sedimentation rate decreases to a constant value of ～0.04 m/ka. Our data confirm that OSL dating using widely distributed fine-grain quartz has great potential for dating deep-sea sediments. Because luminescence methods use clastic materials, they do not depend on the presence of biogenic carbonate. As a result it is now likely that we can establish a chronology in regions of the ocean that were previously undatable.     

Luminescence dating of ephemeral stream deposits around the Palaeolithic site of Ifri n'Ammar (Morocco)

The prehistoric site of Ifri n'Ammar is situated in northeastern Morocco, in the northern prolongation of the Middle Atlas Mountains. It is a key location in unravelling the history of anatomically modern humans (AMH) in northern Africa as it reveals Middle and Late Palaeolithic occupation phases since ∼170 ka. Whilst the archaeological sequence within the rock shelter has been well studied, the timing of landscape dynamics around Ifri n'Ammar is still poorly understood. This study therefore aims to establish a detailed chronology of the Wadi Selloum profile at the apron of the shelter, based on optically stimulated luminescence (OSL) dating of ephemeral stream deposits. Coarse-grain quartz was used for single-grain and multiple-grain dating procedures to investigate the luminescence properties of these deposits and to get more accurate age information concerning the phases of human occupation. Continuous wave OSL (CW-OSL) revealed a dominant fast component for all quartz samples. The dose distribution of the uppermost samples showed overdispersion values >25% and significant positive skewness. We identified partial bleaching as the main source of scatter in the equivalent dose (D_e) distribution. The lowermost sample appeared to be close to signal saturation. The shapes of the dose response curve varied widely between aliquots and coarse quartz grains exhibited therefore very different dose saturation behaviours among aliquots. With fully saturated dose response curves (DRCs), meaningful D₀ values were assumed for D_e estimation.The eight OSL samples yielded stratigraphically consistent ages ranging from 1.3 ± 0.2 ka to 76 ± 5 ka, thus reaching the Middle Palaeolithic period. Moreover, a pottery shard dated to 7.4 ± 0.6 ka (Early Neolithic period) by thermoluminescence (TL), perfectly matched the Holocene OSL samples extracted at the same depth of the profile. In summary, our results point to fluvial aggradation during OIS 5.1, the late glacial period, and the Holocene.     

Optical dating of the upper 22 m of cored sediments from Daihai Lake,northern China

Daihai Lake is one of the largest lakes in the mid-latitude of northern China. Previous environmental change investigations using the sediments from the lake have been mainly focused on the last 13 ka. In 2006, we drilled an 80-m borehole on the southwest coast of the lake. Here we report the results of initial optical dating of the upper 22-m sediments from the core. Most of the samples allow separation of the 4–11 μm fine-grained and 45–63 μm medium-grained quartz, both of which were used for equivalent dose (D_e) determination. Dose recovery test experiments with the single-aliquot regeneration-dose (SAR) protocol indicate that a preheat at 240 °C for 10 s combined with a cut-heat of 240 °C is suitable for these samples. The D_e values show marked discrepancy between the two grain size fractions with the fine-grained quartz yielding up to over 50% higher D_e values than the medium ones for some samples. We consider the OSL ages for the samples from upper ～10 m to be overestimated. The main cause of the overestimation is attributed to the incomplete bleaching of the sediment grains at deposition. The OSL ages for the lower part of the sequence are considered to be reasonable age estimates which provide useful temporal constrains on the deposition of the sediments for the period of 20–40 ka.     

Dating the Kawakawa/Oruanui eruption: Comment on “Optical luminescence dating of a loess section containing a critical tephra marker horizon,SW North Island of New Zealand” by R. Grapes et al.

An IRSL age of 17.0 ± 2.2 ka (and a “mean age” of ca. 19 ka) reported by Grapes et al. [Grapes, R., Rieser, U., Wang, N. Optical luminescence dating of a loess section containing a critical tephra marker horizon, SW North Island of New Zealand. Quaternary Geochronology 5(2-3), 164–169.] for the Kawakawa/Oruanui tephra, and other ages associated with a loess section in New Zealand are untenable: age data presented are inconsistent, no formal statistical treatments or error determinations were undertaken in age analysis, and the ages proposed are seriously at odds with multiple radiocarbon age determinations on tephra sequences bracketing the Kawakawa/Oruanui tephra and with palaeoenvironmental evidence elsewhere for the time period concerned. We suggest that the bulk polymineral IRSL ages on the tephra and encapsulating loess deposits were underestimated in part because of contamination of the loess by the integration of younger materials during slow deposition and continuous modification by upbuilding pedogenesis. Single-grain luminescence assays may reveal such contamination. A ¹⁴C-based age of ca. 27 ± 1 ka cal BP (2σ), reported in 2008, currently remains the best estimate for the age of eruption of the Kawakawa/Oruanui tephra.     

Holocene climate changes in westerly-dominated areas of central Asia: Evidence from optical dating of two loess sections in Tianshan Mountain,China

Optical dating was applied to two loess-paleosol sections (Lujiaowan and Shuixigou) from the northern piedmont of Tianshan Mountain, Xinjiang province, China. The two sections are over 200 km apart and have a similar depositional sequence, which consists of two paleosol layers embedded by one loess layer. Two difficulties were met in optical dating. First, because the sections are located on the slope of the mountain, it was found that some cliff debris, with coarse grains (>200 μm), were mixed with the eolian sediments by rainfall, especially in the paleosol layers. Second, the optically stimulated luminescence (OSL) signals of quartz grains from the deposits were too dim to obtain a reliable equivalent dose (D_e). The 63–90 μm K-feldspar grains were separated to decrease the debris portion, and they yielded bright infrared stimulated luminescence (IRSL) signals. A multiple-elevated-temperature post-IR IRSL (MET-pIRIR) procedure was applied to determine D_e. Comparing the optical dating ages of the two sections, the Lujiaowan (LJW) and Shuixigou (SXG) sections recorded almost the same depositional process during the Holocene. The ages of the two loess layers (2.44–3.38 ka at LJW; 2.47–4.36 ka at SXG) suggested that one drought event happened widely in this westerly dominated area. The same drought event 2.5–3.5 ka ago also happened in the Chinese Loess Plateau (CLP), where the summer monsoon dominated. However, the paleosol development period (6.6–4 ka) in the study area was distinguished from the monsoon dominated area (8–4 ka), which suggests an arid early Holocene in the westerly area.     

OSL and IRSL dating of raised beach sand deposits along the southeastern coast of Norway

Raised beach sand deposits along the southeastern coast of Norway were dated by optical (OSL) and infrared stimulated luminescence (IRSL) and the quartz and K-feldspar luminescence characteristics were described. Due to the poor quartz luminescence characteristics, only a limited number of samples were suitable for OSL dating. More promising are the K-feldspar extracts, with typical K-feldspar luminescence characteristics and no sign of fading. For equivalent dose (D_e) determination, sand-size quartz and feldspar extracts were used, applying a single aliquot regenerative (SAR) protocol. Both, OSL and IRSL D_e estimates show a wide distribution, unexpected for beach deposits. The calculated OSL and IRSL age estimates were generally in good agreement and the correctness of the ages was confirmed by independent age control. Because only a limited number of the quartz samples were suitable for OSL dating, IRSL dating of the K-feldspar represents an alternative to OSL quartz dating.     

Quartz OSL dating of sand dunes of Late Pleistocene in the Mu Us Desert in northern China

The Mu Us Desert, located in the northwestern fringe of the East Asian monsoon region, is sensitive to climate variability. The desert is characterized by mobile, semi-fixed and fixed sand dunes. Alternating units of dune sands and sandy palaeosols in the Mu Us Desert imply multiple episodes of dune building and stabilization, in response to the ebb and flow of the East Asian monsoon. Desert evolution and climatic change of high-resolution in the Mu Us Desert are still poorly understood due to limited numerical dating results. In the present study, 19 samples collected from five sand dune sections along a northwest–southeast transect in the Mu Us Desert were dated using quartz optically stimulated luminescence (OSL) and single aliquot regenerative-dose (SAR) protocol. Internal checks of the OSL dating indicate that the SAR protocol is appropriate for equivalent dose (D_e) determination for the samples under study. Combined with the lithologic stratigraphy and the luminescence chronology, the sand dune development in the Mu Us Desert during the Late Pleistocene is discussed. Our results indicate that the sand was mobilized approximately at 91 ka, 71 ka, 48–22 ka, 5 ka, 1 ka, and 0.44 ka; the sand was fixed approximately at 65 ka and Holocene Optimum period in the interior Mu Us Desert. The Mu Us Desert formed at least before ～144 ka, and has shown increasing aridity in the Late Pleistocene.     

OSL-dating the Quaternary landscape evolution in the Vértes Hills forelands (Hungary)

Fluvial, colluvial, and aeolian sediments were dated by optically stimulated luminescence (OSL) on quartz to improve the chronological framework for Quaternary sedimentation and landscape evolution in the forelands of the Vértes Hills (central Hungary). The separated quartz was suitable for age determination based on an OSL SAR protocol. Most samples have asymmetric equivalent dose distributions and OSL ages were calculated by the mean, central, and minimum D_e values. Considering geomorphology and earlier age data from the area, the central D_e values seem most appropriate for age calculation. A fan on the geomorphological level QV in the western foreland of the Vértes Hills was deposited 79–75 (±8) ka ago. In the south-eastern foreland an alluvial fan on level QIIb is at most 42 ± 4 ka old. Fluvial incision and aggradation occurred 16–10 (±1) ka ago on the geomorphic surface QIIa. Loess is 14 ± 1 ka old, and slope sedimentation was active 11–9 (±1) ka ago. Our OSL data demonstrate that in the north-western foreland of the Vértes Hills wind remained an important agent after the last glacial times, into the early Holocene (9–8 ± 1 ka) and was able to accumulate large aeolian dunes.     

Direct measurement of the fast component of quartz optically stimulated luminescence and implications for the accuracy of optical dating

The usual practice in optical dating is to derive an equivalent dose (D_e) (and hence age) from integration of the initial part of the measured optically stimulated luminescence (OSL) signal. This ‘bulk’ OSL signal is known to comprise several semi-independent components, each of which decays at different rates during measurement, and thus contributes a different proportion to the bulk signal as measurement time progresses. Data are presented here which show a strong dependence of D_e on the bulk signal integration interval, with reduced D_e for later signal integration intervals resulting from lower medium component D_e values. This dependence leads to two problems: (i) deciding which signal integral to choose, and (ii) the possibility that all bulk signals will provide systematic age underestimation due to medium component signal contributions. Isolating the fast component of the bulk OSL signal provides a solution to both problems and several methods of achieving this are assessed; an efficient new method is described which is incorporated in to standard single-aliquot regenerative-dose measurement sequences. This method involves the direct measurement of the fast-component signal using infrared (830 nm) stimulation of quartz at 160 °C, prior to the standard bulk OSL measurement with 470 nm stimulation. It is shown that the measured quartz infrared stimulated luminescence signals resolve pure fast-component signals and provide D_e estimates consistent with those from signal deconvolution. This approach can only be applied to samples with relatively bright luminescence emissions, but in these cases is expected to provide a more robust estimate of palaeodose.     

Re-evaluation of the chronology of the palaeolithic site at Jeongokri,Korea, using OSL and TT-OSL signals from quartz

Seven samples were collected from sediments at the Palaeolithic site of Jeongokri, Korea, known for the first discovery of Acheulian-like handaxes in East Asia. Optically stimulated luminescence (OSL) ages obtained from chemically purified quartz from the upper five samples are in stratigraphic order, but the ages of the lower samples are not. The OSL signal of the oldest samples occurs well above the saturation level of the exponential part of the dose response curve; however, the OSL signal has an additional component that grows linearly at high doses, making it possible to calculate a D_e value and thus an age. However the reliability of calculating D_e using this linear component is not clear. In contrast, the thermally transferred OSL (TT-OSL) signal grows linearly with dose up to at least 1600 Gy, thus permitting its use for dating. The TT-OSL ages are in agreement with those from the OSL for the four uppermost samples, but give older ages for the lower three samples. Ages obtained using TT-OSL are in stratigraphic order and indicate that the oldest artefacts have an age of ～195 ka.     

Optical dating of young deltaic deposits on a decadal time scale

Modern Mississippi Delta sediments were analyzed to investigate quartz OSL signal resetting in large river deltas and test the accuracy of OSL dating on a decadal time scale with the early background subtraction and a recently proposed burial dose estimation procedure. Both fine silt-sized and sand-sized quartz were measured with a modified single-aliquot regenerative dose (SAR) protocol and equivalent dose (D_e) was calculated using different background subtraction methods. Evidence of insufficient bleaching was observed, but the residual signal is equivalent to ∼100 a on average for both sandy quartz and fine silt-sized quartz. It is shown that dose distributions of sandy quartz are affected by the background subtraction. The proportion of aliquots that have D_e in agreement with expectation is significantly larger when an early background is subtracted compared to the late background subtraction. This is, in contrast, not observed for fine silt-sized quartz. Accurate OSL ages were obtained by employing the unlogged minimum age model to D_es of sandy quartz obtained with the early background subtraction method.     

Quartz luminescence dating of Anglian Stage (MIS 12) fluvial sediments: Comparison of SAR age estimates to the terrace chronology of the Middle Thames valley,UK

Quartz optically stimulated luminescence (OSL) is increasingly being used to constrain the depositional age of fluvial and glaciofluvial sequences over orbital (Milankovitch) timescales within the British Isles. Few of these previous studies have had any age control; however there is some evidence that OSL ages based on the single aliquot regenerative dose (SAR) protocol may be subject to systematic age underestimation as samples approach saturation. In this study, the age of 12 luminescence samples from a chronologically well-constrained site dating to 450 ka from the Thames terrace sequence, southern Britain, was measured using SAR in order to test the performance of the method close to its upper age limit. The characteristics, dose response and thermal stability of the OSL signal in these samples were assessed by investigating equivalent dose (D_e) as a function of stimulation time and component-resolved pulse annealing. Despite the fact that the samples are dominated by the quartz fast component, these results showed that both the medium and slow components have lower stabilities than the fast component, but with the unstable medium component most affecting the initial part of the OSL signal used in dating. Based on isolating the fast component either through curve fitting or eliminating the medium component using the early background subtraction method, OSL ages up to 450 Gy were found to compare well with the expected age of the site of 450 ± 23 ka. In contrast, a systematic age underestimation of 10% was manifested at lower doses when using the initial part of the OSL signal, contaminated by the medium component. These results suggest that the early background subtraction method should be used when dating in the non-linear part of the growth curve as it provides a better separation of thermally unstable signals and represents a more convenient approach than curve fitting in well-behaved samples.     

Optical luminescence dating of a loess section containing a critical tephra marker horizon,SW North Island of New Zealand

A new IRSL dataset is presented for the age and setting of a critical Late Glacial Maximum tephra isochron marker. The rhyolitic tephra, known as the Kawakawa Tephra, occurs as a 14 cm thick layer within a 5.9 m thick loess section overlying alluvial gravels in the Rangitikei River valley, SW North Island of New Zealand. Ages range from 21 at the base to 5 ka near the top of the loess and bracket an age of 17.0 ± 2.2 for the tephra. The new IRSL ages are in agreement with published and unpublished luminescence ages from other localities of loess, sand and ash above and below the tephra and of the tephra itself, that indicate an age of ca. 19 ka for the Kawakawa Tephra. This age is considerably younger than the generally accepted ¹⁴C 27.1 ka cal yrs BP age of the Kawakawa Tephra and highlights an unresolved discrepancy between the two dating systems.     

High resolution OSL and post-IR IRSL dating of the last interglacial–glacial cycle at the Sanbahuo loess site (northeastern China)

Northeastern China is located in the East Asian monsoon region; it is sensitive to both high and low latitude global climate systems. Loess deposits in the region have considerable potential as sensitive archives of past climate changes. However, research into loess deposition and climate change in this region is restricted by the lack of independent age control. In this study, coarse-grained quartz SAR OSL and K-feldspar post-IR infrared (IR) stimulated luminescence (post-IR IRSL; pIRIR₂₉₀) methods have been used to date the Sanbahuo loess site in northeastern China. The quartz OSL characteristics are satisfactory. The measured pIRIR₂₉₀ D_e's do not vary significantly with IR stimulation temperatures between 50 °C and 260 °C; a first IR stimulation temperature of 200 °C was adopted. Dose recovery tests were performed by adding different laboratory doses to both laboratory bleached (300 h SOL2) samples and natural samples; the results are satisfactory up to ∼800 Gy. Resulting quartz OSL and feldspar pIRIR₂₉₀ ages are in good agreement at least back to ∼44 ka; beyond this feldspar pIRIR₂₉₀ ages are older. The feldspar ages are consistent with the expected age of the S1 palaeosol (MIS 5). There appears to have been a period of fast loess deposition at ∼62 ka, perhaps indicative of winter monsoon intensification with a very cold and dry climate that lead to a serious desertification of dunefields in northeastern China.     

Timing for high lake levels of Qinghai Lake in the Qinghai-Tibetan Plateau since the Last Interglaciation based on quartz OSL dating

Qinghai Lake is situated in the northeast of the Qinghai-Tibetan Plateau (QTP). Its size and proximity to the junction of three major climate systems make it sensitive to climate changes. Some investigations on shorelines of Qinghai Lake suggested highstands during MIS 3, but to what extent the lake level was higher than today is yet undetermined. Others proposed that the maximum highstands probably dated to MIS 5. It has also been shown that the lake level 120 m higher than today occurred at around 12 ka. Most of these previous ages were obtained using ¹⁴C dating or multiple-aliquot IRSL/OSL dating. For ¹⁴C dating, because of the dating limit (<40 ka) and the lack of suitable dating materials in this arid area, it is difficult to establish reliable chronological control. In the present study, seven samples collected from lacustrine deposits (five samples) and sand wedges (two samples) were dated using quartz optically stimulated luminescence (OSL) with the single aliquot regenerative-dose (SAR) protocol. OSL dating results showed that (1) the lake had experienced two high lake levels, one was in MIS 5 and another in early to middle MIS 3; (2) no evidence of high lake levels in MIS 4 has been found; (3) the alluvial gravels, whose surface is at an elevation of ～3246 m, were formed at least 28.8 ± 2.3 ka ago, and the widespread sand wedges within the alluvial gravels were formed during the period of 15.1–28.8 ka, which implied that the lake level had not reached an elevation of ～3240 m after 28.8 ± 2.3 ka.     

Comparison of paired quartz OSL and feldspar post-IR IRSL dose distributions in poorly bleached fluvial sediments from South Africa

A comparative study using quartz optically stimulated luminescence (OSL) and feldspar post-infrared infrared stimulated luminescence (post-IR IRSL) was undertaken on Quaternary fluvial sediments from an unnamed tributary of the Moopetsi River in South Africa. The aim is to assess whether the post-IR IRSL signal can be used to date incompletely bleached sediments. Several post-IR IRSL signals using varying stimulation and preheat temperatures were investigated; of these the post-IR IRSL₂₂₅ signal was deemed most appropriate for dating because it bleached most rapidly. The feldspar post-IR IRSL₂₂₅ equivalent dose (D_e) values from this site are consistently larger than those from quartz OSL, probably due to differences in the bleaching characteristics of the two signals. Additionally, the post-IR IRSL₂₂₅ D_e values within a sample showed less variation in precision than the quartz D_e data, possibly due to greater averaging between grains in the feldspar small aliquots. The agreement between ages based on the OSL and post-IR IRSL₂₂₅ signals was better for younger samples (<20 ka) than for older ones (>50 ka); the cause of this variation is unclear.     

Applicability of a quartz OSL standardised growth curve for De determination up to 400 Gy for lacustrine sediments from the Qaidam Basin of the Qinghai-Tibetan Plateau

The standardised growth curve (SGC) for quartz OSL has recently been developed as a practical means to reduce measurement times when determining palaeodoses using quartz of aeolian sediments, especially loess and desert sand from the same section or the same geographical area. In the present study, we test the performance of SGCs for lacustrine sediments of three cores in the Qaidam Basin of the Qinghai-Tibetan Plateau (QTP) in China. A total of nine samples were collected (three samples from each of the three cores), and silt-sized (38–63 μm) quartz was extracted for the experiment. The results demonstrated that: (a) Nine samples display similar dose–response curves up to a regeneration dose of 600 Gy using single aliquot regenerative-dose (SAR) protocol, suggesting the existence of a standardised growth curve for lacustrine sediments in the Qaidam Basin; (b) For samples with D_es of up to ～400 Gy, the D_es determined by the SGC are in agreement with the D_es by the SAR protocol, suggesting that the SGC approach could be used for D_e determination up to a dose of ～400 Gy for lacustrine samples from the Qaidam Basin of the Qinghai-Tibetan Plateau in China; (c) The saturation dose for these samples is more than 600 Gy, and in the growth curve a linear growth part was observed in the high dose range of >200 Gy.     

MET-post-IR IRSL luminescence dating of cobbles buried in fluvial terraces in the Northern Chinese Tian Shan

Cobbles can be used as an alternative to the conventionally employed sand-sized mineral luminescence dating. In piedmont environments, cobbles are much more abundant than sand-sized material. The IRSL₅₀ signal has been widely used in previous studies due to its greater sensitivity to exposure events. However, it is well known that the low temperature IRSL signal is more prone to fade than elevated temperature post-IR IRSL signal. In this study, to test the reliability and applicability of cobble sub-surface elevated temperature IRSL luminescence dating, six light-color granite cobbles and two sand-sized samples from silty sand lens were collected from a high terrace of Manas River on the northern piedmont of Chinese Tian Shan. A modified multi-elevated-temperature post-infrared infrared stimulated luminescence (MET-post-IR IRSL) protocol was applied. The age-temperature (A-T) plateau of MET-post-IR IRSL measurement was combined with the conventional age-depth (A-D) plateau in luminescence-depth profile to evaluate the resetting and fading of MET-post-IR IRSL signals. Uncertainties of grain-sizes of K-feldspar within solidified slices were also explored by μ-XRF mapping of potassium content. The A-T plateau was identified between MET-post-IR IRSL₁₇₀ and MET-post-IR IRSL₂₂₅ signals of one cobble, which suggested completeness of bleaching before burial and negligible anomalous fading during burial. This cobble yielded MET-post-IR IRSL₂₂₅ ages of 15.8 ± 2.6 ka and 19.0 ± 3.2 ka for top and bottom side, respectively. These MET-post-IR IRSL₂₂₅ ages were consistent with independent coarse-grained quartz MAM OSL ages (15.7 ± 3.6 ka and 14.8 ± 2.6 ka) of two sand-sized samples. The MET-post-IR IRSL₂₂₅ age of 16.0 ± 1.2 ka for the bottom side of another cobble was also consistent with the independent age, even without the A-T plateau. It was inferred to be caused by anomalous fading of MET-post-IR IRSL signals other than that stimulated at 225 °C by refering to the A-D plateau observed. Our results show that MET-post-IR IRSL measurement can be employed to determine the burial ages of cobbles. The A-T plateau, complemented with the A-D plateau, could be used to assess the reliability of burial ages of cobble luminescence dating from the view of bleaching and fading.