Examining quartz OSL age underestimation for loess samples from Luochuan in the Chinese Loess Plateau

When using quartz OSL to date loess samples from the Chinese Loess Plateau, it has been reported that the agreement between OSL ages and the independent ages is limited to the samples younger than ～70 ka with a corresponding D_e of ～230 Gy, and a sample with an expected age of 780 ka was dated to 107 ka, corresponding to 403 Gy. The growth curves of these samples do not saturate at doses of 700 Gy, and a linear growth part was observed for doses higher than 200 Gy. However, the maximum measured age of ～100 ka imply that the D_e determined using this linear part of a growth curve could be problematic, or that the quartz OSL signal is not as stable as previously thought and has a barrier age of ～100 ka. In the current study, we examine the reasons for the age underestimation. We examined the shape of growth curves, anomalous fading, thermal stability, etc. The results show that, for the loess samples examined, quartz OSL does not fade anomalously, and the barrier age of ～100 ka is due to the fact that the OSL signals are less thermally stable, the lifetime of 0.311 Ma at 20°C obtained is much smaller than those for quartz samples from other regions such as Australia (～100 Ma).     

Historical mortars dating from OSL signals of fine grain fraction enriched in quartz

In the last years the mortar dating through Optically Stimulated Luminescence (OSL) techniques has become a viable support for chronological estimations (date of construction or restoration episodes) of historical buildings. However, the dating of mortar has still open issues mainly regarding the assessment of the bleaching degree of quartz, the analysis of the OSL processes for this type of samples and the need to do appropriate tests for the most correct evaluation of the equivalent dose. This paper discusses the results obtained by OSL dating (blue diode stimulation) on the polymineral fine grain phase, enriched in quartz, extracted from lime mortar samples collected from different sites. Thermal transfer effects, through the behaviour of Equivalent Dose (ED) and recovery tests, degree and time of bleaching were studied. For each mortar sample the adjacent brick was collected; in some cases, sampling of the bricks bracketing a mortar layer was a possibility, thus obtaining a direct comparison with the standard thermoluminescence (TL) dating on the bricks. The results obtained show, for this set of samples, the possibility of dating the mortars through the use of the fine grain fraction provided of a suitable chemical-physical preparation procedure and the verification of the bleaching conditions.     

Rapid denudation of Higher Himalaya during late Pliestocence, evidence from OSL thermochronology

Optically Stimulated Luminescence (OSL) of quartz, with closure temperatures of 30–35°C in conjunction with Apatite Fission Track (AFT; closure temp. ～120°C) and ⁴⁰Ar-³⁹Ar (biotite closure temperature ～350°C), were used to obtain cooling ages from Higher Himalayan crystalline rocks of Western Arunachal Himalaya (WAH). Cooling age data based on OSL, AFT and Ar-Ar thermochronology provide inference on the exhumation — erosion history for three different time intervals over million to thousand year scale. Steady-state exhumation of ～0.5 mm/yr was observed during Miocene (>7.2 Ma) till Early Pleistocene (1.8 Ma). Onset of Pleistocene glacial/interglacial conditions from ～1.8 Ma formed glaciated valleys and rapid erosion with rivers incising deep valleys along their course. Erosion enables midcrustal partial melts to move beneath the weak zone in the valley and causes an erosion-induced tectonic uplift. This resulted in a rapid increase in exhumation rate. The OSL thermochronology results suggest increased erosion over ～21 ka period from Late Pleistocene (2.5 mm/yr) to Early Holocene (5.5 mm/yr) and these are to be contrasted with pre 1.8 Ma erosion rate of 0.5 mm/yr. Enhanced erosion in the later stage coincides with the periods of deglaciation during Marine Isotope Stages (MIS) 1 and 2. The results of the present study suggest that in the present setting OSL thermochronology informed on the short-term climatic effect on landscape evolution and techniques like the AFT and ⁴⁰Ar-³⁹Ar provided longer-term exhumation histories.     

Investigating the resetting of OSL signals in rock surfaces

There are many examples of buried rock surfaces whose age is of interest to geologists and archaeologists. Luminescence dating is a potential method which can be applied to dating such surfaces; as part of a research project which aims to develop such an approach, the degree of resetting of OSL signals in grains and slices from five different cobbles/boulders collected from a modern beach is investigated. All the rock surfaces are presumed to have been exposed to daylight for a prolonged period of time (weeks to years). Feldspar was identified as the preferred dosimeter because quartz extracts were insensitive. Dose recovery tests using solar simulator and IR diodes on both K-feldspar grains and solid slices taken from the inner parts of the rocks are discussed. Preheat plateau results using surface grains and slices show that significant thermal transfer in naturally bleached samples can be avoided by keeping preheat temperatures low. Equivalent doses from surface K-feldspar grains were highly scattered and much larger than expected (0.02 Gy to >100 Gy), while solid surface slices gave more reproducible small doses (mean = 0.17±0.02 Gy, n = 32). Neither crushing nor partial bleaching were found to be responsible for the large scattered doses from grains, nor did the inevitable contribution from Na-feldspar to the signal from solid slices explain the improved reproducibility in the slices. By modelling the increase of luminescence signal with distance into the rock surface, attenuation factors were derived for two samples. These indicate that, for instance, bleaching at a depth of 2 mm into these samples occurs at about ∼28% of the rate at the surface. We conclude that it should be possible to derive meaningful burial doses of >1 Gy from such cobbles; younger samples would probably require a correction for incomplete bleaching.     

A Western Mediterranean amphora fragment from ed-Dur

A previously published amphora fragment from ed-Dur with incuse Latin letters is discussed. Comparanda are adduced from sites in the western portion of the Roman empire.     

OSL and TL characteristics of fine grain quartz from Mongolian prehistoric pottery used for dating

The OSL, post-IR OSL and pulsed post-IR OSL applied to polymineral grains and calculated by fitting to the data the contributions from fast, medium and slow components revealed that the polymineral samples under study are dominated by the medium component. An increase in D _e ’s with increasing integration intervals was observed, which is considered as an indication of increasing medium and decayed fast component; and the equivalent doses obtained using different components or minerals reflect also the shape of the dose distributions. The identified fast component in polymineral sample has photoionization cross section of 1.2±0.02 × 10^?17 cm². The present study shows the usefulness of the application of different luminescence techniques combined with fitting procedures as a check which should be adopted in dating protocols. Based on luminescence ages obtained on poly-mineral grains from prehistoric pottery samples from the Boroo settlement, Mongolia, which are in agreement with independent age control by ¹⁴C on charcoal material, it is argued that the manufacturing of Xiongnu — pottery at this site lasted until ca. 130±75 AD.     

谈《哀江南赋》的史诗性和自传性

庾信是南北朝文学的集大成者,《哀江南赋》是他的代表作品。在《哀江南赋》中作者以史诗之笔深切描写了梁朝由盛而衰以至灭亡的全过程,抒发了个人亡国之恨、乡关之思、身世之悲。这种寓时代乱离于个人哀怨的情感内容是对赋体的一次重大开拓,史诗性和自传性是它的特色。     

Researching and Editing the Selective Edition of the Tibetan Epic Gesar

Gesar is a great heroic epiccreated collectively byTibetans.For thousands ofyears,it has been circulatingfar and wide within Tibetanareas and has been loved byTibetans.Gesar represents anhistorical pinnacle of ancient Ti-betan culture.As not only a crys-tallization of Tibetan's intelligence,but also a cultural treasure house,Gesar is of high academic and aestheticvalue.     

Testing the standardized growth curve (SGC) to OSL dating coastal sediments from the south Bohai Sea, China

It has been suggested that the standardized growth curve (SGC) method can be used to accurately determinate equivalent dose (D_e) and reduce measurement time. However, different opinions regarding the applicability of the SGC method exist. In this paper, we evaluated quartz OSL SGCs of marine and coastal sediments of different grain sizes and different cores in the south Bohai Sea in China, and tested their applicability to the determination of D_e values. Our results suggested as follows: (1) The SGC method is applicable to both multiple- and single-aliquot regenerative-dose (MAR and SAR) protocols of OSL dating and efficiently provides reliable estimates of D_e. (2) Finesand quartz of different palaeodoses showed highly similar dose-response curves and an SGC was developed, but old samples using the SGC method have large uncertainties. (3) For coarse-silt quartz, two different types of dose-response curves were recorded: low-dose (≤60Gy) and high-dose (≥100Gy). The growth curves of low-dose quartz were similar to each other, facilitating the use of SGC in D_e estimations, but errors tended to be larger than those obtained in the SAR method. For high-dose (100–300Gy) quartz, the SGC was also found to be reliable, but there was large uncertainty in D_e (>300Gy) estimation. We suggest that SGC could be employed for the dating of marine and coastal sediments dating using either MAR or SAR OSL protocol and either fine-silt, coarse-silt or fine-sand quartz.     

莫高窟北区出土"阿剌忒纳失里令旨"残片

本文对敦煌莫高窟北区出土编号B163：46蒙古文残文书进行了系统的考察,并认为该文书很可能是1324年出镇沙州的诸王阿剌忒纳失里颁发给吐蕃地区某个招讨司的令旨。文书书于阿剌忒纳失里驻镇沙州期间。基本内容为对招讨司有关军事事务的请示的答复。     

Investigations on the degree of bleaching of quartz OSL signals using modern aeolian dust from western Loess Plateau, China

Optically Stimulated Luminescence signal of quartz extracted from modern aeolian dust with known maximum age (about decades) was analyzed in terms of degree of bleaching. The results of dose recovery tests show that the modified double single-aliquot regenerative-dose protocol with the early background subtraction is robust for dating these modern dusts using small aliquots. Bleaching of these dusts is discussed based on the distribution of De values in histograms, scatter plots of D_e versus sensitivity corrected natural OSL signal and comparison between measured D_e and expected D_e. The results indicate that most dusts were completely bleached but some dusts were not completely bleached. For those incompletely bleached dusts in Lanzhou area, the maximum OSL age overestimation is up to ～1 ka, which might be caused by fast deposition accompanied by heavy sand/dust storms. The research suggests that cautions should be given to OSL ages younger than 1 ka in the western China close to deserts.     

Optically stimulated luminescence (OSL) dating investigations of rock and underlying soil from three case studies

Three rock samples and associated underlying surface (floor) soils of geoarchaeological significance from Greece, Sweden and a modern surface stone-sample from a Danish site were investigated using OSL dating. Thin slice, sub-samples, from drilled core surfaces were prepared. A single-aliquot regenerative-dose (SAR) protocol was used on whole rock slices to estimate the laboratory equivalent dose. Laboratory tests showed that the SAR protocol successfully corrected for sensitivity changes and that a known laboratory dose could be measured accurately.