Luminescence dating of marine sediments from the Sea of Japan using quartz OSL and polymineral pIRIR signals of fine grains

Luminescence dating has long been used for chronological constraints on marine sediments due to the ubiquitous dating materials (quartz and feldspar grains) and its applicability over a relatively long time range. However, one of the main difficulties in luminescence dating on marine sediments is partial bleaching, which causes age overestimations. Especially, partial bleaching is typically difficult to be detected in the fine grain fraction (FG) of marine sediments. The recently developed feldspar post-IR IRSL (pIRIR) protocol can detect non-fading signals and thus avoid feldspar signal instability. In the current study, fine grains were extracted from a gravity core in the northern Sea of Japan, and the aim is to test the feasibility of using different luminescence signals with various bleaching rates to explore the bleaching conditions of fine grain fraction in marine sediments. The results suggest that the quartz OSL signal and polymineral pIRIR signals at stimulation temperatures of 150 °C and 225 °C (pIRIR₁₅₀ and pIRIR₂₂₅) of FG were well bleached prior to deposition. The OSL ages were used to establish a chronology for this sedimentary core and the resulting age-depth relationship is self-consistent and comparable with radiocarbon dates. We conclude that different luminescence signals with various bleaching rates can be used to test the bleaching conditions of fine grain fraction in marine sediments; and the luminescence dating can be applied to marine sediments with great potential.     

Testing the application of quartz and feldspar luminescence dating to MIS 5 Japanese marine deposits

The applicability of both quartz and feldspar luminescence dating was tested on twenty-five samples from a marine succession now forming a coastal cliff at Oga Peninsula, Honshu Island, Japan. The quartz optically stimulated luminescence (OSL) signal shows thermal instability and linear modulated (LM)-OSL analysis revealed the dominance of a slow component. When compared with independent age control provided by two marker tephras, the quartz OSL ages grossly underestimate the depositional age. In contrast, potassium (K)-rich feldspar is a suitable dosimeter when measured using post-IR infrared stimulated luminescence (IRSL) at 225 °C (pIRIR₂₂₅). Scanning electron microscope (SEM) analyses on the feldspar extracts revealed that the grains are amorphous with small crystalline inclusions; using standard internal dose rate parameters, this would result in a too large dose rate. Dose rates were calculated using the observed grain size of 40 ± 20 μm with an assumed K concentration of 12.5 ± 0.5%. The fading corrected pIRIR₂₂₅ ages agree well with independent age control, and the sediments of the Katanishi Formation were deposited between 82 ± 6 and 170 ± 16 ka. This study demonstrates that pIRIR dating of feldspar is a powerful chronological tool for the dating of sediments of volcanic origin.     

Effects of the size of the test dose on the SAR protocol for quartz optically stimulated luminescence dating of loess in the eastern Tibetan Plateau

Dating of quartz by optically stimulated luminescence (OSL) has been revolutionized with introduction of the test dose (TD) in development of a measurement sequence known as the single-aliquot regenerative-dose (SAR), whereby a valid sensitivity correction for the luminescence signal is provided in the measurement cycle. However, the size of the TD used in the SAR protocol remains controversial. Previous studies show that the TD has little effect on the equivalent dose (D_e) for young samples in luminescence dating in which the applicability of different deposits varies greatly in different regions. However, detailed studies are lacking on how TD size affects SAR–OSL results of samples with a relatively high D_e range. In this study, typical loess samples with high D_e values (∼60 Gy–∼250 Gy) from the eastern Tibetan Plateau were selected to investigate the effects of variation in TD size on the quartz SAR–OSL protocol. Dose recovery tests show that a known dose could be recovered successfully by applying different TDs. Test dose size has an effect on shapes of regenerated dose–response curves (DRCs) and has different influences on D_es and characteristic saturation doses for quartz samples with a high dose range. A TD size of 20%–30% D_e is a good compromise for Tibetan loess with D_e of ∼60–120 Gy in the quartz SAR protocol, and a TD size larger than 30% should be considered for samples with a larger D_e. The results of this study highlight the importance of TD size in the SAR–OSL protocol for quartz samples with a high dose range.     

Exploring the potential of luminescence methods for dating Alpine rock glaciers

Rock glaciers contain valuable information about the spatial and temporal distribution of permafrost. The wide distribution of these landforms in high mountains promotes them as useful archives for the deciphering of the environmental conditions during their formation and evolution. However, age constraints are needed to unravel the palaeoclimatic context of rock glaciers, but numerical dating is difficult. Here, we present a case study assessing the potential of luminescence techniques (OSL, IRSL) to date the inner sand-rich layer of active rock glaciers. We focus on the signal properties and the resetting of the signal prior to deposition by investigating single grains. While most quartz shows low signal intensities and problematic luminescence characteristics, K-feldspar exhibits much brighter and well-performing signals. Most signals from plagioclases do not show suitable properties. Luminescence signals far below saturation indicate distinct but differential bleaching. The finite mixture model was used to determine the prominent populations in the equivalent dose distributions. The luminescence ages represent travel times of grains since incorporation into the rock glacier and hence, minimum ages of rock glacier formation. Luminescence ages between 3 ka and 8 ka for three rock glaciers from the Upper Engadine and Albula region (Swiss Alps) agree well with independent age estimates from relative and semi-quantitative approaches. Therefore, luminescence seems to have the potential of revealing age constraints about processes related to the formation of rock glaciers, but further investigations are required for solving some of the problems remaining and reducing the dating uncertainties.     

ESR dating of optically bleached quartz grains from Plio-Pleistocene to Holocene coastal dune deposits (Wilderness-Knysna area,South Africa): a comparison with luminescence

Five Plio-Pleistocene to Holocene aeolian quartz samples from the coastal dune deposits of the Wilderness-Knysna area (South Africa) previously dated by OSL were selected for ESR dating. Samples were processed following the Multiple Centre approach and using the Multiple Aliquot Additive dose method. Aluminium (Al) and Titanium (Ti) signals were systematically measured in all samples.Our study shows that ESR results obtained for Middle Pleistocene to Holocene samples may be strongly impacted by (i) the presence of a significant high frequency noise in the ESR spectra acquired for the Ti signals and (ii) the choice of the fitting function employed. In particular, if not taken into account, very noisy spectra can lead to a significant overestimation of the true ESR intensity measured for the Ti–H signal. These sources of uncertainty are however not sufficient to remove the ESR age overestimations. Consequently, our results indicate that the Al and Ti ESR signals of these quartz samples have not been fully reset during their aeolian transport.While this work contributes to improve our understanding of the ESR method applied to quartz grains, and especially of the potential and limitations of the Ti signals, it also provides additional baseline data to illustrate the existing variability among quartz samples of different origins or sedimentary context. Our results are consistent with previous studies by confirming that the Ti–H signal shows the best potential for the evaluation of low dose values (<100 Gy for these samples), whereas it becomes inappropriate for the higher dose range, and the Ti–Li–H (option D sensu Duval and Guilarte, 2015) should be used instead.Beyond the methodological outcome, this ESR dating study also provides a useful addition to the existing chronology of the aeolian deposits in this region. In particular, new (and possibly) finite numerical age results were obtained for the two oldest samples, constraining the aeolianite landward barrier dune and the coversand formations to the MIS 10-8 and Pliocene, respectively.     

Investigating the components of the optically stimulated luminescence signals of quartz grains from sand dunes in China

The optically stimulated luminescence (OSL) signals from quartz consist of several physically distinct components, which are commonly referred to as fast, medium and slow components. In this study, the OSL components of quartz from the Taklimakan Desert and the Hunshandake sandy land in north China are investigated. Our results show that the relative contributions of OSL components to the bulk OSL signal can be significantly different among quartz grains from both deserts. Laboratory dosing, optical bleaching and heating experiments are used to test their effects on the relative contributions of quartz OSL components. It is found that cycles of dosing and optical bleaching have insignificant impact on the relative contributions of quartz OSL components, while heating to high temperature (500 °C) can significantly enhance the contribution of the fast component to the bulk OSL signals, especially for quartz samples from the Taklimakan Desert. Such results suggest that the different heating history of natural quartz grains plays an important role in controlling OSL components. Additionally, the quartz grains from the Hunshandake sandy land can easily be distinguished from those of the Taklimakan Desert, by using a ternary plot of fast-medium-slow components. The quartz grains from the Hunshandake sandy land exhibit a much stronger fast component than those from the Taklimakan Desert. This can be explained by that the quartz grains from the Hunshandake sandy land are mainly of igneous origin, while most of the quartz grains from the Taklimakan Desert are of low grade metamorphic origin.     

Optically stimulated luminescence dating of single and multiple grains of quartz from perennially frozen loess in western Yukon Territory, Canada: Comparison with radiocarbon chronologies for the late Pleistocene Dawson tephra

Optically stimulated luminescence (OSL) dating of perennially frozen loess was tested on quartz grains extracted from deposits associated with the late Pleistocene Dawson tephra in western Yukon Territory, Canada. OSL samples were obtained from ice-rich loess bracketing the Dawson tephra, while radiocarbon (¹⁴C) samples were collected from the bulk sediments directly underlying the tephra and from a ground-squirrel burrow 2.7 m below the tephra. Here we report the OSL characteristics and ages of the extracted quartz grains, as well as additional radiocarbon ages for samples described in Froese [2002. Age and significance of the late Pleistocene Dawson tephra in eastern Beringia. Quaternary Science Reviews 21, 2137–2142; 2006. Seasonality of the late Pleistocene Dawson tephra and exceptional preservation of a buried riparian surface in central Yukon Territory, Canada. Quaternary Science Reviews 25, 1542–1551]. We refine the time of Dawson tephra deposition to between 25,420±70 and 25,290±80 ¹⁴C a BP. Bayesian analysis of constraining radiocarbon ages places the deposition of the Dawson tephra at between 30,433 and 30,032 cal a BP. Linear modulation (LM) OSL analysis of multi-grain aliquots of quartz showed that the initial part of the decay curve is dominated by a rapidly bleached (‘fast’) component; these samples, however, had relatively dim continuous wave (CW) OSL signals at the multi-grain aliquot (each composed of 80 grains) and single-grain scales of analysis. The single-aliquot regenerative-dose protocol was applied to multi-grain aliquots and single grains to obtain equivalent dose (D_e) values for samples collected from below and above the Dawson tephra. The D_e values were examined graphically and numerically, the latter using the central age, minimum age, and finite mixture models. For multi-grain aliquots, the central age model gave weighted mean D_e values between 30 and 50 Gy, which greatly underestimated the expected D_e of 74–81 Gy for both samples studied. Possible reasons for these underestimations are discussed, and a solution proposed based on single-grain analysis. Measurements of single grains produced D_e values in agreement with the expected D_e, and yielded OSL ages of 28±5 and 30±4 ka for the samples taken from above and below the Dawson tephra, respectively. Examination of individual grains with differing luminescence behaviors showed that a significant number of the measured quartz grains exhibited anomalous luminescence properties that would have compromised the results obtained from multi-grain aliquots. We therefore recommend analysis of individual grains to overcome the age-shortfall from multi-grain analysis of these and similar samples of quartz.     

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.     

Evaluating OSL-SAR protocols for dating quartz grains from the loess in Ili Basin,Central Asia

Late Pleistocene records of loess deposition are a critical archive for understanding terrestrial paleoenvironment changes in Central Asia. The age of loess is not well known for the deserts regions and surrounding high plateaus in Central Asia. Previous studies have shown that there remains a disparity between ages for loess deposition by luminescence and ¹⁴C dating. This study evaluates the potential of optically stimulated luminescence (OSL) to date a loess sequence resting on fluvial sands in the east Ili Basin, Central Asia. The single-aliquot regenerative-dose (SAR) protocol on coarse grain quartz was employed for equivalent dose determinations. The basal fluvial sand returned a secure OSL age, with low overdispersion value in equivalent doses (19 ± 2%) of ca. 36 ka and provides a close, but maximum age estimate (within 5 ka) on the initiation of loess deposition. However, the loess yielded high overdispersion values for equivalent doses and age reversals, coincident with diffuse paleosols; indicating that pedoturbation with loess deposition may be a dominant process. OSL ages between ca. 45 and 14 ka calculated using a maximum age model and OSL ages from other sites in the Basin suggests that the latest major period of loess deposition was between 70 and 10 ka ago. A future hypothesis to test based on these analyses is that there may be three periods of heightened loess deposition at ca. 45, 35 to 19 and 14 ka, when desert source areas to the west were particularly dry.     

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.     

Optically stimulated luminescence dating of a Holocene beach ridge plain in Northern Jutland, Denmark

This study presents results from 20 optically stimulated luminescence (OSL) ages from one of the world's largest beach ridge plains, the Jerup beach ridge plain at the base of the Skagen Spit in the northernmost part of Jutland, Denmark. The OSL ages were obtained using quartz and a SAR protocol, and used to establish a chronology for the beach ridge plain and for the underlying coastal plain. The accuracy of the chronology is tested both by laboratory tests (recuperation, recycling ratio and dose recovery) and by comparison with independent age controls, e.g. previously reported radiocarbon dates, map sources, anecdotal evidence and settlement names. It is concluded that the OSL signals are internally consistent, and that the derived OSL ages are in good agreement with a large range of independent age controls. The ridge plain is shown to cover a time span from 1000 to 2700 years ago; this chronology is more detailed and precise than those previously available, and gives an average beach ridge formation rate of 15 yr/ridge and an average lateral migration rate of 2.0 m/yr. This study adds to the growing knowledge that OSL dating has a large potential for establishing detailed and precise chronologies in coastal marine sediments, including beach ridges.     

Testing the accuracy of quartz OSL dating using a known-age Eemian site on the river Sula, northern Russia

Quartz optically stimulated luminescence (OSL) forms the basis for the chronology of Weichselian ice advances in Arctic Eurasia developed over the last few years. There is almost no age control on this chronology before 40 ka, except for some marine sediments correlated with marine isotope stage (MIS) 5e on the basis of their palaeofauna. Results from more southern latitudes have shown that dose estimates based on quartz OSL and the single aliquot regenerative (SAR) dose procedure may underestimate the age of MIS 5e deposits. Here we use the same method to date well-described marine sediments, thought to have been deposited during the very beginning of the Eemian interglacial at 130 ka, and exposed in two sections on the river Sula in northern Russia. Various quality-control checks are used to show that the OSL behaviour is satisfactory; the mean of 16 ages is 112±2 ka (σ=9 ka). This represents an underestimate of 14% compared to the expected age, a discrepancy similar to that reported elsewhere. In contrast to SAR, the single aliquot regeneration and added (SARA) dose procedure corrects for any change in sensitivity during the first OSL measurement. The SARA results are shown to be 10% older than those from SAR, confirming the geological age estimate and suggesting that SAR ages may underestimate older ages (larger doses), despite their good performance in the younger age range.     

Optically stimulated luminescence dating of aeolian sand in the Otindag dune field and Holocene climate change

The dune system in Otindag sand field of northern China is sensitive to climate change, where effective moisture and related vegetation cover play a controlling role for dune activity and stability. Therefore, aeolian deposits may be an archive of past environmental changes, possibly at the millennial scale, but previous studies on this topic have rarely been reported. In this study, thirty-five optically stimulated luminescence (OSL) ages of ten representative sand-paleosol profiles in Otindag sand field are ob-tained, and these ages provide a relatively complete and well-dated chronology for wet and dry varia-tions in Holocene. The results indicate that widespread dune mobilization occurred from 9.9 to 8.2 ka, suggesting a dry early Holocene climate. The dunes were mainly stabilized between 8.0 and 2.7 ka, implying a relatively wet climate, although there were short-term penetrations of dune activity during this wet period. After ~2.3 ka, the region became dry again, as inferred from widespread dune activity. The "8.2 ka" cold event and the Little Ice Age climatic deterioration are detected on the basis of the dune records and OSL ages. During the Medieval Warm Period and the Sui-Tang Warm Period (570-770 AD), climate in Otindag sand field was relatively humid and the vegetation was denser, and the sand dunes were stabilized again. These aeolian records may indicate climate changes at millennial time scale during Holocene, and these climatic changes may be the teleconnection to the climate changes elsewhere in the world.     

Quartz and polymineral luminescence dating of Japanese loess over the last 0.6 Ma: Comparison with an independent chronology

There are only a few luminescence dating studies of loess sediments in Japan, but interleaved with these deposits are many well-described tephras of known age based on ¹⁴C and fission track analysis; these independent age controls provide an opportunity to test the reliability of loess luminescence ages. This study provides such a comparison at two sites in central Honshu, the largest island in the Japanese archipelago. Samples were collected from sequences of interleaved volcanic tephra and loess deposited on a Middle Pleistocene river terrace in the Niigata Prefecture and on an Early to Middle Pleistocene dissected fluvial surface at in the Tochigi Prefecture, Honshu. Equivalent doses (D_e) were estimated from fine grains (4–11 μm) using both polymineral IR-OSL and (post-IR) blue-OSL, and quartz blue-OSL. The blue-stimulated luminescence signals could be represented by up to three exponentially decaying components; only the most light sensitive of these components was used in the final D_e estimation. Almost all the estimates of D_e from polymineral IR-OSL are smaller than those from polymineral (post-IR) blue-OSL and quartz blue-OSL, whereas the latter two are in good agreement. The blue-light stimulated luminescence ages using the most light sensitive component are shown to be in good agreement with the independent control, up to 500 ka. Although the IR-OSL signals underestimate the known age, a simple laboratory fading test is found empirically to correct for this underestimation. We conclude that the most rapidly blue-stimulated luminescence signals from quartz extracted from our loess samples give reliable ages, and that future loess dating studies should concentrate on these signals.     

Implications of broad dose distributions obtained with the single-aliquot regenerative-dose method on quartz fine-grains from loess

Six samples were collected from a section of Peoria Loess in Eustis, North America, for optically stimulated luminescence (OSL) dating of quartz, and all except one (LV90) produced narrow dose distributions. A comparative study was conducted on this sample and on a ‘well-behaved’ sample (LV91), involving other dating methods and examination of the quartz OSL. These investigations revealed differences in the quartz OSL growth with dose, OSL response to thermal treatments and the range of components within the OSL signals. An ultra-fast component was found in LV90 that displayed a higher rate of sensitivity change than the fast component and this had a malign influence on the determination of the equivalent dose. The distinctive luminescence characteristics of LV90 imply either a change in wind dynamics and/or the source area for the silt.     

Quartz OSL and K-feldspar pIRIR dating of a loess/paleosol sequence from arid central Asia,Tianshan Mountains,NW China

Loess deposits surrounding the high mountainous regions of arid central Asia (ACA) play an important role in understanding environmental changes in Eurasia on orbital and sub-orbital time scales. However, problems with dating loess in ACA have limited the interpretation of climatic and environmental data, especially Holocene data. We selected a typical loess/paleosol sequence (LJW10) on the northern slope of the Tianshan Mountains in ACA consisting of 280 cm of loess with multiple paleosols formed in the upper 170 cm of the section. We applied quartz OSL dating to coarse-grained (63–90 μm) fractions, and newly developed K-feldspar pIRIR dating protocols to both coarse-grained and medium-grained (38–63 μm) fractions of the samples from LJW10 section. Internal checks of the quartz OSL dating indicate that the single-aliquot regenerative-dose protocol on large aliquots (5 mm) is appropriate for equivalent dose (D_e) determinations and that the quartz ages of the loess samples are likely to be reliable. Luminescence characteristics and internal checks of the pIRIR dating indicate the pIRIR signal at a 170 °C stimulation temperature with a 200 °C preheat can be used for both coarse-grained and medium-grained D_e determinations. Anomalous fading tests for the pIRIR 170 °C signal indicate the pIRIR signals are stable and the anomalous fading of the pIRIR 170 °C signal can be ignored. Sunlight bleaching tests of the loess indicate the residual dose for the pIRIR 170 °C signal can also be ignored as it corresponds to only ∼9 years for the medium-grained K-feldspar and ∼85 years for the coarse-grained K-feldspar. The pIRIR ages of five medium-grained and coarse-grained K-feldspar samples are consistent with coarse-grained quartz OSL ages, and both the medium-grained and coarse-grained ages increase uniformly with depth, indicating these pIRIR ages are reliable. Based on the coarse-grained quartz OSL ages, and on coarse-grained and medium-grained K-feldspar pIRIR ages, an age-depth model for the paleosol-loess sequence was established by using a Bacon age-depth model. This model suggests eolian loess deposition began by at least ∼16 ka ago and that paleosol development on these eolian loess deposits began ∼5.5 ka, continuing to the present, with periods of high effective moisture at 5.5–4.9, 4.6–4.1, and 3.4–3.1 ka. This sequence suggests overall relative aridity during the early Holocene and an increase in effective moisture beginning ∼5.5 ka during the mid-late Holocene in ACA.     

Single-grain optically stimulated luminescence dating of quartz temper from prehistoric Intermountain Ware ceramics,northwestern Wyoming,USA

This study applies single-grain optically stimulated luminescence (SG OSL) dating of quartz sand temper to Intermountain Ware ceramics recovered from four archaeological sites in northwestern Wyoming, USA. We show that SG OSL dating can strengthen and further refines existing archaeological site chronologies in certain settings. The SG OSL results are compared to multi-grain infrared stimulated luminescence (IRSL) dating of the polymineral (feldspar and quartz) silt fraction in the ceramic paste of the same sherds. Results from the two methods are statistically indistinguishable, although coarse-grained quartz SG OSL ages have consistently lower standard error terms due to higher relative sensitivity and avoidance of anomalous fading calculations. Moreover, the SG OSL results produced precision at two-sigma standard error greater than or equal to associated calibrated radiocarbon ages. SG OSL dating of quartz temper from Intermountain Ware ceramics provides more reliable site occupation timing than radiocarbon dating, which can be conditioned by incorporation of old wood and contamination from young soil carbon. This study highlights the importance of SG OSL dating on sherds from buried contexts when exposure to wildfires may have occurred, as ceramics recovered from the ground surface of one site after a high-intensity fire produced near-modern apparent ages, suggesting they were thermally reset during the fire. We suggest SG OSL should be applied to date similar ceramics with quartz temper to determine site age and bolster regional chronologies.     

Age comparison by luminescence using quartz and feldspar on core HPQK01 from the Pearl River delta in China

Reliable chronology is critical for reconstructing estuarine delta process. In this study, detailed chronological framework has been performed on a core HPQK01 (52 m in depth) from the central Pearl River delta (PRD) of China. Both quartz OSL and feldspar post-IR IRSL (pIRIR) methods for late Pleistocene sediments, as well as radiocarbon dating for Holocene sediments, were applied to date the core. Results show that quartz OSL ages range from 125 ± 18 ka to 58 ± 6 ka, and that all of them were minimum ages due to the OSL signal saturation. Feldspar pIR₂₀₀IR₂₉₀ protocol shows some overestimation in dose recovery test, with the recovered to the given ratio of 1.2, while a ratio of around 1 was obtained for feldspar pIR₅₀IR₂₅₀ signals. Robust ages have been obtained from feldspar fading corrected pIR₅₀IR₂₅₀ dating with ages ranging from 150 ± 17 ka to 98 ± 12 ka. AMS ¹⁴C results suggest that subtidal-intertidal zone was deposited during the middle Holocene from 8.21 ± 0.19 cal ka BP to 4.99 ± 0.25 cal ka BP. The sedimentology of core HPQK01 record two marine transgressive-regressive cycles. Based on the dating results, the lower fluvial sediment unit (T2) could be correlated to marine isotope stage (MIS) 6, and the lower marine unit (M2) was deposited during MIS 5. A sedimentary hiatus occurred with age range of from MIS 4 to MIS 2. Since middle Holocene, another marine stratum (M1) has been accumulated. Overall, our findings suggest that feldspar pIRIR dating method has the potential to establish the Quaternary chronostratigraphic framework of the PRD for samples with ages within 150 ka.     

Timing of Holocene lake highstands around Dawa Co in inner Tibetan Plateau: Comparison of quartz and feldspar luminescence dating with radiocarbon age

Lakes over the inner Tibetan Plateau (TP) are very sensitive to the regional environmental transformations and climate changes. Well-preserved lake sediments around these lakes provide critical geomorphological and sedimentary evidence that can be used to infer the past hydroclimate changes. In this study, a lacustrine section from a sandy shoreline (∼74 m above the modern lake) situated to the northwest of modern Dawa Co in the inner TP was investigated using both luminescence and radiocarbon dating methods. Our results demonstrated: (1) the quartz optically simulated luminescence (OSL) dating yielded much younger ages (∼4 ka) than that of the post-infrared IRSL (pIRIR) dating of the K-feldspar fraction; (2) fading test showed g-values ranging between 1.34 and 4.46%/decade for quartz OSL signals, which is considered to be responsible for the underestimation of the corresponding ages; (3) the AMS ¹⁴C age of the charcoal sample from the section is in line with the K-feldspar pIRIR₂₂₅ ages, confirming the reliability of the pIRIR₂₂₅ dates and the underestimation of the quartz OSL ages. The anomalous fading of quartz OSL signals and the consequent age underestimation have been reported in several other lakes on the TP, we presented here for the first time firm evidence of the phenomenon with the help of a robust independent control of AMS ¹⁴C age of the charcoal. Based on the pIRIR₂₂₅ and AMS ¹⁴C ages, we conclude that Dawa Co underwent a prominent highstand during the early Holocene (∼9–7 ka), which was probably controlled by the large amounts of glacial meltwater input and the increased monsoonal precipitation.     

Challenges of dating quartz OSL samples with saturated grains: Lessons from single-grain analyses of low dose-rate samples from Victoria Falls,Zambia

A suite of samples from an extensive aeolian sandscarp near Victoria Falls, Zambia was used to explore several different methods of calculating optically stimulated luminescence (OSL) ages that account for the effects of saturated quartz grains. Beta dose rate heterogeneity and early OSL signal saturation of the samples exacerbate the impact that saturated grains have on the equivalent dose (D_e) values calculated. Saturated grains that cannot calculate D_e values are often rejected but the minimum burial dose information they contain can have a significant impact on a sample's average D_e value. This study compares multiple techniques for combining luminescence measurements that enables inclusion of this data and their sensitivity to a criterion that rejects grains with early OSL signal saturation. The methods tested are found to have different advantages and disadvantages, but reasonable agreement between the D_e values they calculate suggests that including data from saturated grains makes a more significant difference to D_e values calculated than the specific method used to combine the data.