In the quest for extending the upper age limit of optically stimulated luminescence (OSL) dating of quartz, it was shown that violet stimulated luminescence (VSL) may be a promising candidate. However, difficulties in the application of the single aliquot regenerative dose (SAR) protocol for VSL has been reported in previous studies. In this study, a set of experiments was carried out to investigate the behaviour of the VSL signal under different measurement conditions with the aim to improve the SAR VSL protocol in terms of passing the procedural tests of the SAR protocol, i.e., recycling ratio, recuperation and dose recovery. The validity of an optimised SAR protocol was then evaluated on four coarse-grained quartz samples from Sardinia, for which previously reported OSL and post-IR IRSL ages are available. Our result showed that all measured aliquots meet the recuperation, recycling ratio and dose recovery criteria, indicating that the proposed protocol is suitable for the studied samples. The obtained VSL and reference ages agree within uncertainty (2σ) for most of the samples except one sample with a largest expected equivalent dose of ∼320 Gy, for which the VSL significantly (∼50%) underestimates despite satisfactory dose recovery result. This underestimation is most likely due to trapping sensitivity change between the natural and all subsequent regenerated VSL signals induced by the first preheating in the SAR procedure, which is likely dose dependent. To minimise sensitivity change, the sensitivity-corrected multiple aliquot regenerative dose (SC-MAR) protocol was applied. The SC-MAR protocol yields VSL ages in agreement with reference ages for two samples (1σ); the other two samples show overestimation. We show that the observed age overestimation can be explained by incomplete resetting of the natural signal after 7 days SOL2 exposure used for the SC-MAR procedure. Bleaching experiments confirm variable bleaching behaviour among different samples. However, it is unclear whether this different bleaching behaviour arises from measuring samples with different bleaching histories, mineralogical compositions, or VSL source trap properties. 相似文献
古湖岸堤是湖面波动的地貌证据,可以用来重建古湖泊演化.古湖岸堤沉积物的准确测年是应用此地貌学证据重建湖泊演化的关键.以我国兴凯湖最低一级湖岸堤——大湖岗为研究对象,采用石英小片技术,应用单片再生剂量法(SAR)对大湖岗2个不同位置的剖面风成砂质沉积物(共13个样品)进行了光释光(OSL)测年.样品石英组分的光释光衰减曲线特征表明,样品的释光信号以快组分为主,预热坪和实验室剂量恢复实验结果表明,SAR法可以用来测量兴凯湖古湖岸堤样品的等效剂量.通过分析样品等效剂量分布情况和比较3种年龄模型(平均值模型、中值模型和最小值模型),认为大湖岗湖滨砂质沉积物在沉积埋藏前石英光释光信号晒退完全,获得的OSL年龄是可信的.年代结果表明,大湖岗采自不同位置的2个剖面的年代范围一致,且各个剖面中所有年代均随地层顺序变化;另外,2个样品的OSL年龄与同层位的炭屑样品的14C年代结果在误差范围内一致,进一步表明OSL测年技术可以获得可靠的兴凯湖岸堤沉积物的年龄.尽管与前人使用热释光(TL)测年方法研究大湖岗形成年代有较大差别,本文认为兴凯湖最低一级古湖岸堤——大湖岗形成于距今约1.24-0.50 ka. 相似文献
Linking the timing of glacial episodes and behaviour to climatic shifts that are documented in ice and marine sedimentary archives is key to understanding ocean-land interactions. In the NW Scottish Highlands a large number of closely spaced (‘hummocky’) moraines formed at retreating glacier margins. Independent age control on one palaeo-glacier limit is consistent with the timing of Younger Dryas (YD) glaciation in the area, but adjacent glacier lobes have remained undated due to the lack of sites and material for 14C dating. Direct dating of ice-marginal moraines using optically stimulated luminescence (OSL) techniques has never been attempted before in Scotland, but if successful, they may be the most appropriate methods for constraining the age of sediment deposition in the absence of organic material. Coarse-grained quartz and K-feldspar minerals from supraglacial sheet flow deposits and glacilacustrine sediments within ice-marginal moraines were analysed using the single-aliquot regenerative-dose (SAR) protocol. Independent age control and clear geomorphological relationships indicate that all samples should yield YD or post-Last Glacial Maximum (LGM) ages. Quartz OSL shine down curves showed low luminescence sensitivity, significant medium-to-slow components, a weak fast component, and scattered SAR data; Linearly Modulated-OSL (LM-OSL) measurements confirmed that the fast component was weak or absent. In contrast, feldspar infrared stimulated luminescence (IRSL) was highly sensitive with excellent SAR data. However, SAR data from 3 mm diameter aliquots of feldspar (200 grains) give higher than expected equivalent doses (De) by an order of magnitude. SAR measurements of small clusters of feldspar grains (ranging from 1–8) considerably broaden the apparent De distribution, but even the lowest value is about 2–3 times the expected De. Two possibilities arise to explain the quartz and feldspar data: (1) that glacial sequences in the NW Highlands re-work inherited (older) glacial deposits and that some of the pre-Devensian existing glacial landforms have only been modified during Devensian glaciation; or (2) that the sedimentary processes operating in these ice-marginal environments are not conducive to adequate bleaching of quartz and feldspar grains. Our study implies that ice-proximal supraglacial sediments from this region in NW Scotland reflect older ages of deposition, but dating YD sediments has not been possible. 相似文献