【作者】 陈淑娥；

【导师】 黄春长； 李虎侯；

【作者基本信息】 陕西师范大学 ， 自然地理学， 2003， 博士

【摘要】 全新世是人类文明迅速发展进步的时期，揭示全新世气候的变化规律对于认识现阶段地理环境及其发展趋势具有重要意义。为了阐明全新世气候的波动特点及其区域性差异，断代就显得尤为重要。由于黄土中所含的化石、木质、炭屑等适于其它方法测年的物质很少，同时，全新世黄土受年轻有机碳和无机碳的影响较大，致使全新世黄土类沉积物的测年迄今仍缺少理想方法。释光测年，特别是光释光测年，由于研究的对象是石英、长石等矿物，而广泛应用于测定沉积物及焙烧过物质最后一次曝光事件或受热事件后埋藏至今所经历的时间。在光释光测年中，单片技术以其用量少、不需要归一化、精度高等特点，近年来备受人们关注。黄土作为一种风积物，主要矿物是长石和石英，光释光信号在搬运漂浮于空中时可以被阳光曝晒“回零”。本文通过渭河流域全新世黄土的光晒退实验，地表黄土样品的D_e值测定，细颗粒单片的预热、反常衰退、红外暴露实验，说明释光测年在全新世黄土中应用的可行性及单片再生剂量法（SAR）在黄土细颗粒中的适用性；为了从黄土中分离出足够的粗颗粒，进行了纯石英和长石的氢氟酸（HF）和氟硅酸（H₂SiF₆）溶蚀实验，黄土粗颗粒石英溶蚀分离实验；通过细颗粒单片、多片的BLSL、IRSL和Post-IR OSL，热释光，及粗颗粒石英的BLSL的年代测定，选择适于全新世黄土的释光测年方法，并建立了渭河流域全新世黄土的年代序列。 主要结论如下： 1．黄土细颗粒样品的碘钨灯晒退实验和地表黄土样品的D_e值测定表明，黄土样品不仅光释光信号极易被光晒退，而且黄土沉积时光释光信号已经被“回零”，所以黄土样品完全适于用光释光进行测年。 2．用单片再生剂量法（SAR）测定黄土样品的D_e值时，用固定的实验剂量释光信号校正后，再循环比（Recycling Ratio）都在1左右，说明对释光灵敏度的变化起到了很好地校正作用；校正后，OGy再生剂量释光信号与自然信号的比率都在5％以下，信号的回复可以忽略不计。同时，D_e值的测量精度普遍比多片法高。 3．黄土细颗粒样品的反常衰退实验、预热实验和红外暴露实验都表明，Post-IR OSL信号热稳定性好。BLSL信号由两部分组成，一部分既可以被蓝光激发，也可以被IR激发，另一部分只能被蓝光激发，这两种类型的陷阱在不同的预热温度中分布不均匀。所以，黄土细颗粒混合矿物的BLSL可能来自石英和长石，Post-IR OSL与纯蓝光释光信号（无IR暴露）相比，更富含石英的OSL。同时，红外暴露后留下了稳定的高能量的陷阶电子，使得POSt－IR OSL信号的热稳定性较 IRSL和 BLSL好。 4．溶蚀实验表明，用40％HF溶蚀40min对石英的损失太大，不适合黄土中石英的分离。用 30％氟硅酸（20ml冶）溶蚀约 6天，分离黄土中的石英颗粒，既可以溶蚀掉长石颗粒，又对石英的损失较小。 5．对渭河流域37个黄土样品进行了细颗粒单片再生剂量法和多片法的BLSL、IRSL和 POSt－IR OSL，及粗颗粒单片（SAR）BLSL的年代测定，其中，用单片法测的年代，在误差范围内与多片法测的年代一致。同时，用单片再生剂量法测小干3ha的黄土细颗粒样品，SLSL、IRSL和POSt－IR OSL测的年代在误差范围内基本相同，接近预估年代；对于3ha—10ha的黄土细颗粒样品，一般Post＜ OSL测的年代更接近预测值；对于大于10ha的样品，一般IRSL测的年代普遍太小，多数 BLSL年代也偏小，而 P。St－IR OSL年代则有些偏大，取 BLSL和 POSt－IR OSL年代的平均值一般可以得到理想的年代。 6．根据释光测年的结果，并结合内插法推算，可以得出关于渭河流域全新世黄土一古土壤序列的基本年代框架，即全新世黄土开始堆积的时间为 11．skaB．P，古土壤形成开始于 S．ska B．P，古土壤成壤结束的时间是 3ha B．P，类似于眉县 QQC剖面的复合古土壤 S。当中的黄土夹层，其堆积年代为 6．oka B．P．一5．oka B．P，，现代表土层的形成开始于1．ska B．P。更多还原

【Abstract】 The Holocene was a period that had a close relation with mankind, so it could be very important to bring to light the laws of Holocene climatic variations for understanding nowadays geographic environment and its trend of development. Dating would be particularly important in order to elaborate the characteristic of climatic variations and its regional discrepancy. As there are less such materials in loess as fossil, plants, slag , etc, which could be used for dating, luminescence dating, especially optically stimulated luminescence dating, was extensively applied to aeolian deposits, for its dating materials were minerals, such as quartz and feldspar. Recently, single-aliquot technique has been paid close attention in OSL dating, because of its higher precision, less quantity, as well as normalization is avoided in single-aliquot. Loess is silt-sized aeolian deposit and is mainly composed of quartz and feldspars, its OSL signals can be set to zero by exposure to light. In order to elaborate the applicability of OSL to loess, especially single aliquot regenerative protocol (SAR), involving stimulation of the same disc with an infra-red laser diode followed by blue LEDs to polymineralic fine-grains of loess, such explanations as light bleaching, preheat, anomalous fading, prior-IR exposure were investigated in this paper. For drawing adequate coarse grains from loess, quartz and feldspars, as well as loess, were etched by hydrofluoric acid and fluorosilicic acid. The sequence of ages of Holocene loess in Weihe Rivier Basin has been established by single-aliquot (SAR) and multiple-aliquot using fine-grains and SAR using coarse-grains. The main results are as fellows:1. The bleaching experiment of loess by iodine tungsten lamp and the equivalent dose (De) of loess estimated by SAR from the earth’s surface indicate that loess can be easily bleached by sunlight, and OSL is suitable for the dating of loess.2. Equivalent dose estimated by SAR, when each natural or regenerated dose OSL measurement is corrected for changes in sensitivity using the OSL response to a subsequent test dose and the recycling ratio is around 1, implies that sensitivity changes have been properly corrected. The sensitivity corrected zero dose regenerated signal is within 5% of the sensitivity corrected natural signal, implies that the recuperation is negligible. Also, the precision of De estimated by SAR is higher than that estimated by multiple aliquots.3. The experiments of anomalous fading, preheat and the effect of prior-IR exposure on OSL stimulated by blue light in polymineral fine grains, indicate that the post-IR OSL signals do not show detectable fading, and has greater thermal stability. It must be noted here that blue stimulated luminescence from polymineral fine grains presumably originate from both quartz and feldspar grains, and it is thus likely that any blue stimulated signal following an IR exposure in our samples will be richer in quartz OSL in comparison to a pure blue stimulated signal without IR exposure.4. When the quartz fraction was cleaned of feldspar grains by etching in concentrated HF for 40min, more quartz fraction was etched away, and this method may be not suitable for the purity of quartz in loess. As quartz fraction in loess is separated by the tedious process of etching with fluorosilicic acid for 6 days, 20ml 30% fluorosilicic acid per gram, not only the feldspars in loess could be removed completely, but also less quartz could be etched away in loess.5. The OSL dating of 37 samples of loess in Weihe River Basin by SAR and multiple aliquot methods, indicates that SAR protocol appears to be applicable to loess and appropriately correcting for sensitivity changes within the regenerated curves, however, there are major difference between the IRSL and Post-IR OSL De determinations that suggest that sensitivity changes relating to either (or both) Natural signals may not be correctly monitored. While SAR is applied to fine grains of loess, the ages of sample which is youn更多还原