post-IR Optically Stimulated Luminescence Research Articles

Early Holocene dust activity variation in the southern Tibetan Plateau and its response to solar irradiance

The Tibetan Plateau (TP) is an important source for long-range-transported Asian dust, however, the past variation of dust activity in the TP is poorly understood. In this study, we analyzed a ∼ 4.8-m aeolian loess-sand sequence from the Yarlung Tsangpo Valley in the southern TP. A closely spaced sampling strategy was used for optically stimulated luminescence (OSL) dating. With single-aliquot regenerative-dose (SAR) OSL and post-infrared (post-IR) OSL protocols, the medium-grained (38–63 μm) quartz fraction was selected to establish a detailed chronology. The two most popular OSL readers (Lexsyg and Risø) were applied to all samples for equivalent dose measurement, and the corresponding comparison shows very good reproducibility of ages derived from the two independent reader systems. A total of 23 luminescence ages were obtained ranging from 6.7 ± 0.3 ka to 11.6 ± 0.7 ka in stratigraphical order. Aeolian sands accumulated during cold-dry Younger Dryas period, and the overlying loess deposited during Early Holocene. Frequency-dependent susceptibility is used to infer pedogenesis intensity or vegetation cover, and coarse grain size fraction is used to reflect the dust activity frequency during Early Holocene. The reconstructed variation of dust activity frequency in the southern TP shows strong cyclicity of ∼ 1 ka, ∼ 0.7 ka and ∼ 0.5 ka with confidence level of >95%, probably indicating that the regional dust activities on centennial and millennium scales are closely related to the changes of the North-Atlantic Oscillation (NAO) phase as response to solar irradiance forcing.

LUMINESCENCE DATING OF AN ANCIENT WALLED SETTLEMENT IN ORKHON VALLEY, MONGOLIA

We investigated the potential of the optically stimulated luminescence (OSL) method to date young (<1000 years) samples collected in the Orkhon Valley Cultural Landscape, Mongolia. Quartz showed an infrared signal; therefore the post-IR OSL method was applied to small aliquots which are considered proxies for single grain measurements. Statistical analysis of the dose distribution produced CAM De of 5.14±0.10 Gy and over dispersion of 47.5%, and MAM De of 3.7±0.6 Gy. Since no partial bleaching was suspected, the analysis of signal composition was done and the fast quartz post-IR OSL lead to De of 4.9±0.2 Gy. Based on the quartz fast component and CAM De we propose the new chronology of ancient construction at 785±80 AD, rather than 906-1125 AD as suggested by archaeological evidence. However, the MAM age is in good agreement with independent age control for construction of the ramparts suggesting the date of reconstruction, collapse or reuse for the square walled enclosure MOR3 during 1090±80AD.

Optical dating of Holocene tidal deposits from the southwestern coast of the South Yellow Sea using different grain-size quartz fractions

The tidal flat deposit provides ideal sedimentary records for paleoenvironmental studies. Reliable chronology is crucial to utilize this archive for deciphering the history of environmental changes. In this study, we applied optically stimulated luminescence (OSL) dating method to a Holocene tidal flat sequence using both coarse-grained (CG, 90–200μm) and fine-grained (FG, 4–11μm) quartz extracts from a sedimentary core (YZ07) in western coast of the South Yellow Sea. The luminescence characteristics of the two grain-size fractions were investigated and then their resulting OSL ages were systematically compared. The results suggested that most tidal flat deposits are well bleached and their FG quartz ages are generally consistent with CG quartz ages, while some samples have CG ages underestimated compared with FG, likely resulted from the K-feldspar contamination for CG quartz. Hence, we applied post-IR OSL dating and pulsed OSL dating techniques; they could overcome the problems caused by feldspar contamination, and yielded identical dates as FG OSL ages. All OSL ages are generally in stratigraphic order; in contrast, the 14C ages are much more disorder and characterized with severe inversions. Finally, the age framework of the tidal flat sequence under this study was constructed based on the 30 OSL ages and one acceptable radiocarbon age. According to the age-depth model, three main periods of sedimentation-rate (SR) variation were identified. These SR changes are probably associated with sea-level rise/fall history, and the depocenter landward/seaward movement as well as the transition of depositional process within the Holocene delta initiation. The depositional environment changes were also reflected in sedimentological features of the tidal flat deposits in our study area.

Investigating the potential of HCl-only treated samples using range-finder OSL dating

Rapid sample preparation and measurement protocols for optically stimulated luminescence (OSL) dating have been investigated as a method of increasing the throughput of samples (e.g. Roberts et al. 2009). Here, we investigate the potential of dating samples treated using only hydrochloric acid (HCl) for providing accurate range-finder ages for quartz. The equivalent dose (De) is underestimated for older samples using a standard single-aliquot regenerative-dose (SAR) protocol, but measurement of the post-IR OSL signal (e.g. Roberts and Wintle, 2003) provides De estimates within 15% of the ‘target fully prepared De’ for two-thirds of samples. The application of a standardised growth curve (SGC) is also investigated. For these dune samples, the most efficient preparation and measurement procedure from which accurate De estimates can be obtained is treatment with HCl-only, measurement of the natural and regenerative post-IR OSL signal, and calculation using a region-independent SGC. A slightly longer protocol incorporating an additional preparation stage of heavy liquid density separation can be used to improve De estimates in samples where feldspar-contamination is thought to be particularly problematic. In practice, these time savings of days to weeks in the preparation and measurement protocols mean that a large number of samples can first be rapidly treated with HCl, the post-IR blue OSL signal measured using a shortened double-SAR protocol, and De calculated by applying an independent SGC before then deciding which samples require full preparation and measurement, rather than the inefficiency of committing time and resources to all samples if this is unnecessary for the context of a particular suite of samples. The potential of this rapid preparation and measurement protocol is discussed in relation to sand dune dating studies.

Sedimentary and OSL dating evidence for the development of the present Hobq desert landscape, northern China

The sedimentary sequence and landscape of the Hobq desert was observed through twelve profiles along five N-S sections extending through the entire desert. Aeolian sands were found to overlie the alluvial, diluvial, and lacustrine sediments in this desert. Optically stimulated luminescence (OSL) dating results were obtained from post-IR OSL signals of quartz fractions of sand samples at the bottom of sand dunes and hills by using the Double-SAR protocol. The OSL ages reveal that the latest sand accumulation began around 19 ka in the northwestern part and 9 ka in the eastern part of the Hobq Desert. Around 7 ka, the sand accumulation was strengthened and extended southward and northward 2 ka to develop the present desert landscape. Our study suggests that the aeolian sand accumulation around 19, 9 and 7 ka resulted from the weakening of the Asian summer monsoon over this region. However, the rapid development of the present Hobq desert landscape since 2 ka was likely triggered by human activities in this desert.

Combined IRSL and post-IR OSL dating of Romanian loess using single aliquots of polymineral fine grains

The paper reports on continuing luminescence investigations of Romanian loess using samples collected from the loess-palaeosol sequence near Mircea Vodă (SE Romania). Previous optically stimulated luminescence (OSL) studies using different grain-sizes of quartz (4–11μm and 63–90μm) yielded discrepant chronologies for the last interglacial–glacial cycle. In this study, a double-SAR protocol is used to determine the age of polymineral fine (4–11μm) grains through their infrared stimulated luminescence (IRSL) and post-IR optically stimulated luminescence (post-IR OSL) emissions in the UV. Laboratory tests confirm the suitability of the protocol for both signals. Fading measurements indicate a significant feldspathic contribution to the post-IR OSL signal. In general, the fading-corrected IRSL and post-IR OSL age results are mutually consistent, and they agree with previously reported OSL ages for fine-grained (4–11μm) quartz. This agreement enhances the reliability of the ages obtained using luminescence signals from fine-grains, and allows more confident correlation of the weakly-developed palaeosol in the uppermost loess unit (L1) with marine isotope stage 3 (MIS3). The fading-corrected ages underestimate the depositional age of older material (units L2–L4), probably owing to limitations of the correction model.

Luminescence Dating of Pseudokarst Speleothems: A First Approach

ABSTRACT Water trickling through the discontinuities of granitic massifs causes slow rock weathering, resulting in mineral deposits within rock fissures (speleothems). Geochemical studies have shown different types regarding the mineral composition: evansite, opal-A, and Al-bearing organic compounds. They grow by accretion of concentric layers, and they are a suitable microenvironment for the settlement of organisms, spores, and pollen grains, which could be used as paleoclimatic records if the speleothems were dated. Among speleothem types, opal-A and evansite usually contain quartz- and feldspar-rich detrital grains. Thus, Optically Stimulated Luminescence (OSL) could be used to date them if detrital grains were sufficiently exposed to daylight (bleaching) before burial within the speleothems. The OSL of such grains was investigated to estimate ages of samples from Northwest Spain. Post-IR OSL (Post-Infrared Optically Stimulated Luminescence) has been used on coarse grains due to the high feldspar content. Results are indicative of complete bleaching of residual geological signals and ages between 0.5 and 3 ka BP.

Dust deposition and climate in the Carpathian Basin over an independently dated last glacial–interglacial cycle

Loess in the Carpathian Basin is some of the thickest and most complete in Europe. Located in the Vojvodina region of the southern Carpathian Basin the Crvenka loess-palaeosol section appears to preserve a detailed climate proxy archive of the last glacial–interglacial cycle. Central to the interpretation of the site is a detailed and independent age model. Here, the results of detailed optically stimulated luminescence (OSL) dating and elevated temperature post-IR infrared stimulated luminescence (post-IR IRSL) dating are presented. Quartz OSL ages appear accurate to about 50–60 ka, where 2D 0 values are reached, while elevated temperature post-IR IRSL yields more accurate ages below this. In line with recent results, the latter signal appears to show negligible fading rates. Two age models are developed that combine (a) OSL and post-IR IRSL ages and (b) OSL ages and ‘expected’ ages from tying unit boundaries to the marine record. If the luminescence model is regarded as accurate, differences between this and the OSL/marine age model raise questions over the accuracy of the latter, as well as the processes controlling the zeroing of luminescence dates. The luminescence based age model is then used to derive the first fully independent reconstruction of climate proxies and accumulation rates from Carpathian loess. Such reconstructions can be used to compare to other independent records without assumptions inherent in correlation-based approaches. The findings demonstrate how variable accumulation rate is at the site, and compared to other independently dated Carpathian loess records. Average values vary north–south but are of similar order throughout the basin. Accumulation rate was highest during the later part of the last glacial, but variation on millennial timescales does not always match shifts in grain-size, suggesting diverse and complex influences. Environmental reconstructions using grain-size and magnetic susceptibility show that no one atmospheric system or air mass can explain the changes in the Carpathian Basin and that millennial-scale variability can only intermittently be tied to North Atlantic Heinrich events. Expanded ice sheets during the peak last glacial, combined with other atmospheric teleconnections, may have served to develop a strong anticyclone in the region. It was likely windier during earlier parts of the last glacial, but Atlantic and Mediterranean moisture was probably less abundant than during more humid interglacials.

Luminescence chronology of the upper part of the Stari Slankamen loess sequence (Vojvodina, Serbia)

A thick Middle and Late Pleistocene loess-palaeosol sequence is exposed at the Stari Slankamen section in the Vojvodina region situated in the south-eastern part of the Pannonian basin, Serbia. The profile exposes an about 45 m thick series of loess intercalated by at least eight pedocomplexes. Ten samples were dated by luminescence methods using a modified single aliquot regenerative dose (SAR) protocol for polymineral fine grains and for quartz extracts from the upper part of the Stari Slankamen loess sequence. The infrared stimulated luminescence (IRSL) and post-IR optically stimulated luminescence (OSL) signals from all polymineral samples showed anomalous fading, suggesting that the post-IR OSL signal is still dominated by feldspar OSL. The ages ranging from 4.6 to 193 ka were obtained after fading correction. These ages indicate that the loess unit V-L1L1, the weakly developed soil complex V-L1S1 and the loess unit V-L1L2 were deposited during marine isotope stage (MIS) 2, 3, and 4, respectively, and also indicate that the loess unit V-L2 is of the penultimate glacial age.

TL and OSL Dating of Sediment and Pottery from Two Syrian Archaeological Sites

Luminescence dating is widely applied nowadays, mainly for archaeological material and artefacts and sediments of all types and origins. However, optically stimulated luminescence (OSL) from archaeological sediment, originated from mud brick buildings has been hardly studied. The archaeological sites of Tall Abu Fahd and Tall Qsubi are located in the Middle Euphrates Valley, Deir ez-Zor district, Syria. These two Bronze Age sites were recently discovered by a Spanish-Syrian team from the Directorate General of Antiquities and Museums (Damascus) and the University of Coruña. Both sites were dated (about 3.5 ka BC) by typological pottery classification. Sediment and pottery samples from these archaeological sites were collected for luminescence dating. Several analytical procedures for obtaining equivalent doses were tested on the sediment samples. Blue OSL from quartz subsamples and IRSL, post IRSL Blue OSL from feldspar contaminated quartz and polymineral subsamples were performed to obtain OSL ages. For the pottery samples, additive dose TL on a coarse grain feldspar contaminated quartz subsample was performed as well. Results have shown agreement among all the luminescence procedures tested on the Tall Abu Fahd site samples after fading correction, showing ages around 2.7 ka BP. Obtained ages from the other site samples show disagreement among quartz blue OSL and the other subsamples. Fading ratios allow correcting age underestimations from the polymineral post-IR OSL signal. However, the polymineral IRSL signal still shows underestimation. Final sediment and pottery ages have shown good agreement. Older <sup>14</sup>C independent age (3.32 ka BP) corresponds to occupational periods of the site while sediment ages are attributed to a post occupation phase.

The estimation of [formula omitted] using the fast and medium components in fired quartz from archaeological site Karakorum, Mongolia

Optically stimulated luminescence (OSL) is used to estimate the radiation dose derived from environmental radiation since the last heating event—the production of brick, tile, terracotta figures and ceramics in the archaeological site Karakorum, Mongolia. The dose distributions of some quartz samples showed a large scatter in the D e obtained using the initial OSL signal. Isolation of components by curve fitting procedure revealed that the characteristics of dose distribution depend on the variability of the ratio fast to medium components within the aliquots considered. Using the infrared stimulation at 220 ∘ C allowed depletion and the individual dose estimation of the medium OSL component, while the post-IR OSL gave less scatter in D e for the fast OSL component. Analytical tools such as D e ( t ) -plots, dose recovery tests and the component-resolved sensitivity changes aimed to identify and to diagnose the OSL signal composition, which can be used to estimate a correct mean D e value.

A comparison of OSL ages derived from silt-sized quartz and polymineral grains from Chinese loess

Recent work (Watanuki et al., submitted) has shown by comparison with independent age control that silt-sized quartz grains extracted from Japanese loess can be used for optically stimulated luminescence (OSL) dating for equivalent doses of up to 425 Gy (∼500 ka at these sites). Further comparison with infrared (IR) stimulated and post-IR blue-stimulated OSL showed that the latter signal gave accurate ages, and was probably dominated by quartz, whereas the former systematically underestimated ages in the range 30–600 ka, and showed fading in laboratory tests. The main source of the loess deposits in Japan is the Chinese mainland; in eastern Asia, loess is widely distributed by the prevailing westerly winds, and one of the main sources is in the western desert areas of China. Unfortunately, independent age control is very unusual in loess deposits in China, and there is little evidence for the accuracy of existing luminescence ages from this material. As an alternative approach, this study builds on the Japanese results by using loess from two Chinese sites, and examining the relationship between single-aliquot regeneration dose IR and post-IR blue-stimulated luminescence ages from polymineral samples, and blue-stimulated quartz luminescence ages. The normalized blue-stimulated OSL intensity from quartz from the eastern site was about 10 times that from the west, suggesting either a different source of material, or (less likely) an increase in quartz sensitivity with transport distance. By comparison with quartz results we conclude that, in our samples of Chinese loess, the post-IR blue-stimulated OSL is the more reliable polymineral signal, when compared with the IR signal. It may nevertheless include a feldspar component, and this should be tested for using laboratory fading experiments.

Equivalent dose determinations for polymineralic fine-grains using the SAR protocol: application to a Holocene sequence of the Chinese Loess Plateau

A single-aliquot regenerative-dose (SAR) protocol, involving stimulation of the same disc with an infra-red laser diode followed by blue LEDs, was applied to polymineralic fine-grains. Infra-red stimulated luminescence (IRSL) and (post-IR) optically stimulated luminescence (OSL) ages are presented for a series of 19 fine-grain (4–11 μm) samples, taken from a loess section (Duowa) in the western Chinese Loess Plateau. There are significant differences between the equivalent doses and, thus, the ages for the IRSL and (post-IR) OSL measurements. Three potential explanations are investigated: incomplete bleaching prior to deposition; thermal transfer of charge; and initial sensitivity change. The question regarding which sequence of ages [IR or (post-IR) OSL] is correct (if either) is not resolved, although the 19 (post-IR) OSL ages yield more consistent results. It is proposed that the `double’ SAR protocol employed may not be correctly monitoring the sensitivity changes relating to either (or both) Natural signals.