Search

Abstract Partial bleaching is a major challenge in OSL (Optically Stimulated Luminescence) dating of flood sediments. Here we investigated both modern and palaeoflood sediments in the North China Plain. It demonstrates that most of the OSL ages for either coarse-grained (CG) or fine-grained (FG) quartz were overestimated in different levels. In the clay-dominated flood deposits, OSL signals of FG quartz from samples at the top of each layer can be bleached to a lower level and therefore give relatively accurate ages. While in silt-dominated flood sediments, the ages of FG quartz are significantly older than those of CG quartz. Ages obtained using the Minimum Age Model (MAM) for CG quartz are the closest to the burial ages of sediments, and the overestimation is mostly in the range of 0.5–1 ka. Although the FG quartz in silt sediments are not suitable for OSL dating the flood events, the OSL ages of FG quartz changes accordingly to the particle-size changes within each silt-dominated layer. The lager the particle sizes are; the older the OSL ages of FG quartz are. The OSL ages of CG quartz are corresponds in an opposite way. It can help to identify floods deposits. Furthermore, the differences of residual OSL ages of FG quartz in different layers in flood sediments may provide more depositional information. [ABSTRACT FROM AUTHOR]

Fluvio-lacustrine terraces along Phung Chu (river) on the central southern Tibetan Plateau indicate that a large palaeo-dammed-lake formerly existed in this area. Based on landscape survey, optically stimulated luminescence (OSL) dating and sedimentary analyses, this research shows that the Phung Chu was blocked and a dammed-lake over 2500 km2 in size formed before 30 ka ago. OSL dating analysis suggests the fluvio-lacustrine sediments were well bleached and yield accurate age estimates for two lake drainage events. The first drainage event took place after 30 ka, resulted in river incision and formed a high terrace at 50 m height from the present river level. The second drainage happened after 3.7 ka, resulted in further river incision and formed the second terrace at 25 m height from the present river level. According to the distribution of the fluvio-lacustrine sediments, active normal faults (particularly the Kharta Fault) in this region and the high gradient slopes after Phung Chu enters the Yö Ri gorge, seismically-induced landsliding is regarded as highly likely to have been the cause of river blockage and associated formation of a dammed-lake, although glacial damming is also a possible cause. The volume of drainages from this dammed-lake may have led to catastrophic flooding and analogous modern lakes represent significant geo-hazard risks to down-river human settlements. As dammed-lakes are special phases in fluvial evolution, often involving river blockage, breakthrough and drastic catchment change, these processes can reveal how tectonic or climatic events modify landforms. However, such tectonic-derived landform changes can also impact palaeo-climate of the region. Thus this study has added new evidence regarding the evolutionary history of a dammed lake including its formation, duration, extent and final drainage, which is crucial for understanding its general landscape process mechanisms and for better assessing geo-hazard risks. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT The Qilianshan [ shan means 'mountain(s)' in Chinese] are important for understanding the Quaternary glaciations which occurred along the north-eastern margins of the Tibetan Plateau (TP). Two sets of moraines identified in the Gangshika Valley on the southern slopes of the Qilianshan, and in the Jindonggou Valley on the northern slopes of the Lenglongling Ridge in the eastern Qilianshan, were dated using optically stimulated luminescence (OSL) dating. The De values of the sediments were determined using single aliquot regeneration (SAR) and 'global standardized growth curve' (gSGC) procedures. The gSGC method was first applied to glacial sediment and proved to be adaptable. Based on De distribution analysis, and a comparison between the ages of coarse-grained (90-125 μm) quartz, we concluded that the minimum age model (MAM) OSL age obtained may be closer to the burial age of the sediments. The first set of moraines in the Gangshika Valley was formed at 18.1 ± 1.8 ka. The second set of moraines in both the Gangshika and the Jindonggou valleys was mainly formed at ∼12.5-10.7 ka, consistent with the Younger Drays chronozone, most probably covering the moraines produced at 14.3 ± 1.4 ka. These results indicate that the glaciers along the Lenglongling Ridge were sensitive to abrupt decreases in temperature. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We report investigations of the optically stimulated luminescence (OSL) signals of sedimentary quartz from different regions of Asia, Africa, Europe and North America using a single-aliquot regenerative-dose (SAR) procedure. We show that variations in the shape of dose response curves (DRCs), or growth curves, of the test dose sensitivity-corrected OSL signals among single aliquots composed of multiple grains can be greatly reduced by normalising the DRCs using one of the regenerative dose OSL signals. We refer to this regenerative-dose normalisation procedure as ‘re-normalisation’. We find a common re-normalised DRC extends to doses of ∼250 Gy for samples that differ significantly in terms of geological provenance, sedimentary context and depositional age. This feature permits the development of a ‘global standardised growth curve’ (gSGC) for OSL signals from single aliquots of quartz. The equivalent dose ( D e ) of an aliquot can be estimated from the natural signal, one regenerative dose signal and their corresponding test dose signals. For the variety of samples investigated, we find that D e estimates obtained from the gSGC are consistent with those obtained using full SAR procedures for doses of up to ∼250 Gy. Use of the gSGC for single aliquots would greatly reduce the time required to estimate the D e values of older samples and for a large number of aliquots. [ABSTRACT FROM AUTHOR]

Quartz has been the main mineral used for optically stimulated luminescence (OSL) dating of sediments over the last decade. The quartz OSL signal, however, has been shown to saturate at relatively low doses of ∼200-400 Gy, making it difficult to be used for dating beyond about 200 thou-sand years (ka), unless the environmental dose rate is low. The infrared stimulated luminescence (IRSL) from feldspars has been shown to continue to grow to higher dose levels than quartz OSL. The application of IRSL dating of feldspars, however, has long been hampered by the anomalous fading effect. Recent progress in understanding anomalous fading of the infrared stimulated luminescence (IRSL) signals in potassium-feldspar has led to the development of post-IR IRSL (pIRIR) protocols and also a multiple elevated temperature (MET) stimulation (MET-pIRIR) protocol. These procedures have raised the prospect of isolating a non-fading IRSL component for dating Quaternary deposits containing feldspars. In this study, we review the recent progress made on (1) overcoming anomalous fading of feldspar, and (2) the development of pIRIR dating techniques for feldspar. The potential and problems associated with these methods are discussed. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the sensitivity change of multiple-elevated-temperature (MET) stimulated post-infrared infrared-stimulated luminescence (MET-pIRIR) signals as a response to irradiation, sunlight bleaching and heating using samples from the Mu Us Desert, central China. A strong dose dependence of MET-pIRIR signal sensitivity was observed. The intensity of the test-dose signals (T x) increase with the pre-dose received. Furthermore, the signal sensitivity can be reset by sunlight bleaching or heating. This suggests that both the electron traps and hole centres in K-feldspar can be bleached by sunlight, and can, therefore, be used for dating. Using the test-dose signal as a monitor for sensitivity change, it was found that the sensitivity (or hole centres) saturate at a higher dose (D 0 = ∼750 Gy) than the sensitivity-corrected signals (or electron traps) (D 0 = ∼400 Gy). We propose a multi-aliquot regenerative-dose (MAR) MET-pIRIR dating protocol, which utilises the high saturation dose of hole centres. This protocol was tested using aeolian sediments from north China with ages ranging from 0 to 470 ka. It was found that, compared to the dose limit of ∼800–1000 Gy using the normal MET-pIRIR or pIRIR procedure, the new method can measure a natural dose of up to ∼1500 Gy and produce ages consistent with the expected ages for the samples investigated. [Copyright &y& Elsevier]

A modified multi-elevated-temperature post-IR infra-red stimulated luminescence (MET-pIRIR) protocol is proposed for dating young samples of Holocene age using K-feldspar. The protocol utilizes a five-step MET-pIRIR measurement with a moderate preheating of 200 °C for 60 s, and a narrow IR stimulation temperature increment of 30 °C (i.e., the five measurement temperatures are 50, 80, 110, 140 and 170 °C). Using this method, the residual doses of the MET-pIRIR signals are generally less than 1 Gy. Holocene aeolian samples from Northern China were tested using the 30°C-increment modified MET-pIRIR method. The results demonstrate that similar ages from 140 °C to 170 °C were obtained for our samples, which were consistent with the quartz optically stimulated luminescence (OSL) ages. Based on this observation, the measurement procedures are further simplified to a three-step pIRIR protocol. The first IR stimulation at elevated temperature (110 °C) is used to remove the fading affected signals. This is followed by two steps of IR stimulation at high temperatures (140 and 170 °C) for equivalent dose (De) measurement. Dating results consistent with the expected ages have been obtained at stimulation temperatures of 140 and 170 °C. It is suggested that the first IR stimulation can effectively remove the fading component. The three-step pIRIR method has minimized the experimental procedures, while keeping the age plateau test. [ABSTRACT FROM AUTHOR]

Abstract: A protocol for optical dating of potassium-rich feldspar (K-feldspar) is proposed. It utilizes the infrared stimulated luminescence (IRSL) signal measured by progressively increasing the stimulation temperature from 50 to 250 °C in step of 50 °C, so-called multi-elevated-temperature post-IR IRSL (MET-pIRIR) measurements. Negligible anomalous fading was observed for the MET-pIRIR signals obtained at 200 and 250 °C. This was supported by equivalent dose (De) measurements using the IRSL and MET-pIRIR signals. The De values increase progressively from 50 °C to 200 °C, but similar De values were obtained for the MET-pIRIR signal at 200 and 250 °C. Measurement of modern samples and bleached samples indicates that the MET-pIRIR signals have small residual doses less than 5 Gy equivalent to about 1–2 ka. We have tested the protocol using various sedimentary samples with different ages from different regions of China. The MET-pIR IRSL ages obtained at 200 and 250 °C are consistent with independent and/or quartz OSL ages. [Copyright &y& Elsevier]

Abstract: In luminescence measurements of potassium-feldspar (K-feldspar), both infrared (IR) and blue light (BL) can be used as stimulation sources. Component analysis suggests that the blue light stimulated luminescence (BLSL) measured at 60 °C from K-feldspar can be fitted using three components, namely fast, medium and slow. In order to explore the relationship between the origin of the infrared stimulated luminescence (IRSL) signal and the different components of the BLSL, five sets of experiments were conducted, namely post-IR BLSL (pIR-BLSL), post-BL IRSL (pBL-IRSL), pulse annealing tests, dose response and laboratory fading rate tests. It is observed that most of the IRSL signal can be bleached by BL, while the BLSL signal can only be partially bleached by the IR. The sources for IRSL are mainly associated with the fast and medium components of the BLSL signal. [Copyright &y& Elsevier]