新型GV5000宽频诱导发光测试仪的研制及其应用于筛分无色小颗粒合成钻石和天然钻石

天然钻石中普遍含有聚合氮以及复杂的生长结构,而合成钻石不含氮或含少量单氮并有典型的与合成条件有关的生长结构,利用此类性质可对天然和合成钻石进行区分。但对粒度细小或镶嵌复杂的钻石样品进行检测时,现有仪器由于局限性难以实现有效测量。本文研制了一种新型宝石发光性测试装置——宽频诱导发光测试仪(GV5000),通过对激发光源和滤光片、结构设计和测试方式的研发,实现了可同时观察多个小颗粒样品(最小为0.002 ct)的荧光特征和磷光特征,建立了一种以发光特征差异性作为筛分条件快速、准确筛分无色小颗粒天然钻石和合成钻石的分析方法。应用本方法测试了9015粒样品,并通过红外光谱、光致发光光谱等方法对筛查结果进行验证,表明97%的天然钻石具有蓝白色荧光并无磷光,而合成钻石的发光特征明显区别于天然钻石。本方法避免了样品大小和形状的影响,提高了小颗粒钻石鉴定的准确度和检测效率,对天然钻石的筛查率可达97%,对合成钻石的筛查率可达100%。     

First evidence for episodic flooding events in the arid interior of central Saudi Arabia over the last 60 ka

Although evidence for Quaternary environmental changes in the Arabian Peninsula is now growing, research has mostly been conducted in the United Arab Emirates (UAE) and in the Sultanate of Oman. There have been virtually no recent studies in Saudi Arabia, especially in the central region such as around Al‐Quwaiayh. In this area there are a series of outwash plains developed along the eastern edge of the Arabian Shield that formed in the late Quaternary. Four sedimentary sections, which are representative of the deposits that have accumulated, have been studied and five luminescence ages obtained. These are the first luminescence ages acquired from Quaternary sediments in central Saudi Arabia. The preserved fluvial deposits in the study area have formed during humid events at ca. 54 ka, ca. 39 ka and ca. 0.8 ka. In more recent times aeolian sands have been encroaching on to the distal parts of the outwash plains. Copyright © 2008 John Wiley & Sons, Ltd.     

风成沉积石英绿光释光测年的单片技术

运用再生法进行单片技术测年所面临的主要问题是感量变化。论文探讨了石英绿光释光测年中对感量变化进行校正的方法,然后运用单片技术对沙漠黄土边界带风成沉积沙样进行等效剂量测定。结果表明,单片技术是石英绿光释光测年的理想手段。     

Progress and pitfalls of the SAR protocol for the quartz violet stimulated luminescence (VSL) signal: A case study from Sardinia

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.     

断层崩积楔单片再生法光释光测年:以山西忻定盆地西田探槽为例

为了研究断层崩积楔各部位沉积物光释光信号晒退情况及崩积楔形成年龄,利用中颗粒石英(63~90μm)单片再生法(SAR)对山西忻定盆地西田探槽断层崩积楔3个部位的4个样品进行光释光(OSL)定年。选择一代表性样品(08-OSL-22)进行等效剂量(DE)、LN/TN、循环比率、回授率与预热温度的关系分析,结果表明预热温度260℃、预热时间10 s为样品最佳预热条件。4个样品的测片循环比率基本在0.9~1.1之间,回授率均小于5%,表明所采用的中颗粒SAR法流程可以很好地校正测量过程中产生的释光感量变化,其等效剂量可信。利用等效剂量分布直方图和累积频率图,发现古地形面和坡积物的样品晒退均匀,崩积层样品则较差。对于晒退较差的样品利用累积频率法得到其等效剂量,从而得到崩积楔的近似年龄。最后获得该期崩积楔的形成年龄为(27.09±0.71)ka。     

大渡河上游鸡心堡滑坡形成的古堰塞湖及其环境效应

堰塞湖及其溃决洪水对山地地表过程具有强烈影响, 严重危害山地区域的安全, 对堰塞湖开展相关研究, 可为区域现代堵江风险分析提供参考。以青藏高原东缘大渡河上游支流小金川鸡心堡古滑坡堰塞湖为研究对象, 采用单片再生剂量法与标准生长曲线法相结合的方法对深度约12.5m的湖相沉积剖面上的7个光释光样品测试年代, 并进行了详细的地层学与年代学研究, 恢复该堰塞湖的年代和范围, 重建该古滑坡的规模, 讨论了该古堰塞湖的成因及其环境效应。研究结果表明: 1)研究区在距今约2~3ka发生过一次滑坡堵江事件, 形成鸡心堡古滑坡堰塞湖, 持续一段时间后, 形成最大流量约为2.70×10³m³/s的洪水溃决过程; 2)该古堰塞湖的堵江残留滑坡坝高约150m, 滑坡坝面积约1.41×10⁵m², 体积约4.19×10⁶m³, 堰塞湖的面积约1.84×10⁶m², 库容水量约6.10×10⁷m³; 3)依据现有地质证据以及文献记载初步推测鸡心堡古滑坡是由地震引起的; 4)滑坡坝对现代河道的地貌形态仍然存在影响, 在滑坡坝上游形成较宽的现代河道且河道纵剖面的坡度较小, 滑坡坝后的河道陡峭指数(k_sn)较高。通过研究, 对大渡河流域的古堰塞湖有更全面、科学的认识, 为古地质灾害领域提供了一个研究实例。

     

帕米尔高原瓦恰盆地黄土的石英光释光测年

中亚黄土对研究亚洲内陆干旱化、亚洲粉尘来源、亚洲季风和西风环流变化以及两者在中亚相互作用历史均具有重要意义。中亚南部帕米尔高原不同地貌面上广泛发育有厚约1~2 m的风成黄土沉积,文章对高原东北部瓦恰盆地的两个黄土剖面进行了细颗粒石英光释光测年。结果表明,瓦恰盆地黄土样品石英光释光信号主要源于325℃热释光信号所对应陷阱电子,以快速组分为主。每个样品分别采用石英光释光信号标准生长曲线法（SGC）和全球石英光释光标准生长曲线法（gSGC）获得的等效剂量与其单测片再生剂量法（SAR）实测等效剂量值在误差范围内是一致的,说明SGC法与gSGC法适用于瓦恰盆地的黄土测年。两个剖面黄土样品石英SAR法光释光年龄界于4.7~14.3 ka,沉积速率由早期的0.11 mm/a加速至全新世的0.15~0.18 mm/a。据沉积速率估算剖面1黄土堆积于17.2 ka至2.7 ka之间,主要堆积于末次冰盛期末至全新世晚期,且远比其所在地貌面要年轻。本研究为进一步开展帕米尔高原黄土古环境研究提供了年代框架。

     

山东大黑山岛北庄黄土沉积特征及其环境演变

发育于山东滨海岛屿区的黄土与黄土高原等地内陆黄土相比,是沿海地区轨道尺度气候变化和海平面变化的重要记录,对研究区域古气候古环境演变具有特殊价值。本文通过对山东庙岛群岛大黑山岛北庄黄土剖面钻孔岩芯样品进行光释光（OSL）测年、粒度和磁化率分析,并与黄土高原典型黄土以及山东其他地区黄土进行了对比。研究结果表明,北庄黄土剖面0.5m处OSL年代为26.23±4.92ka,处于晚更新世末期,说明剖面全新世黄土缺失,与区域内其他剖面进行年代对比,可推断北庄黄土主要为末次间冰期以来堆积的黄土。与黄土高原典型黄土相比,北庄黄土为典型风成沉积物,但其平均粒径比黄土高原典型黄土粗,且与同区域其他岛屿上黄土相比粒径具有由南向北逐渐增大的变化趋势,这可能与不同阶段气候变化引起的海面升降而导致的主要物源不同有关。根据北庄黄土粒度和磁化率变化趋势并结合OSL测年结果,将该剖面从上到下划分为古土壤层、黄土层和古土壤层,分别对应着MIS 3~MIS 5气候旋回。因此,大黑山岛北庄黄土剖面记录了末次间冰期以来山东东部沿海地区古气候环境变化进程。

     

古湖岸堤沉积物石英光释光测年研究:以中国东北兴凯湖为例

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.     

Quartz luminescence sensitivity variation in the Chinese loess deposits: the potential role of wildfires

The sensitivity of optically stimulated luminescence (OSL) of quartz grains has been applied to trace the provenances of sediments in various environments. Here, we studied the OSL sensitivity of quartz grains in four sections (Jingyuan, Huanxian, Xifeng and Luochuan) along a west–east transect on the Chinese Loess Plateau (CLP). The quartz OSL sensitivity in the palaeosol units is higher overall than that in the loess units, and it shows an increasing trend from the west CLP to the east CLP. In palaeosol units, it increases by a factor of ~20 along the west–east transect; while in loess units it increases by a smaller degree of 3–5. The change of provenances and the change of distances between the provenances and the loess sections cannot fully account for the large degree of sensitivity variation between the loess and palaeosol units in the central and eastern CLP. We propose that wildfires may have played an important role in enhancing the quartz OSL sensitivity in the palaeosol units in the central and eastern CLP. Quartz OSL sensitivity has the potential to be used as a proxy for palaeowildfires.