摘要
对洛川末次冰期的黄土细颗粒混合矿物红外释光(IRSL)信号异常衰减行为的初步研究结果表明:1)预加热只能部分消除异常衰减对等效剂量测定的影响,不能完全消除这种影响,IRSL异常衰减过程也许存在着热效应和非热效应两种组分;2)对16个已知年龄的马兰黄土(15～70ka)样品细颗粒混合矿物天然IRSL信号的ED值与期望ED值的比较初步显示,马兰黄土细颗粒混合矿物IRSL信号异常衰减不断发生,导致混合矿物IRSL的年龄测定值可能被低估达20%以上。
The preliminary results about anomalous fading of fine-grained polymineral IRSL signal Chinese loess during the Last Glacial Period are reported. First, our preheating experiments show that for longer duration of preheating it removed more anomalous fading IRSL component, although IRSL intensity and IRSL ages are still detectable for the Last Glacial loess samples. Thus it seems that the usage of such preheating will not remove all anomalous fading IRSL components but reduce the fading rate in a dating study. It is also proved that relative high temperature storage for several days cannot fully remove effect of anomalous fading of fine-grained polymineral IRSL signal. Therefore it is possible that anomalous fading in fine-grained polymineral may be divided into a thermal and an athermal dependence on thermal treatments, indicating that such preheating cannot totally remove effect of anomalous fading, but partly lessen it. Secondly, we used fine-grained quartz OSL ages to calculate the IRSL ED expectations for 16 samples in the past 70ka, which can be regarded as the reliable accumulation dose if no fading happened since deposition. Additionally, a standardised growth curve of polymineral grain IRSL signal was constructed by 99 regeneration data points of 33 samples from the Luochuan loess. The natural IRSL intensities of 16 samples used in this study were measured and projected onto this IRSL standardised growth curve to obtain their ED values. The sensitivity changes of IRSL intensity of each sample were corrected by the IRSL signal to test dose as did in single aliquot regenerative dose protocol. By comparing ED measurement and ED expectation of IRSL in the Luochuan loess samples, the information about fading rate in the past 70ka are obtained. It is found that natural polymineral grain IRSL signal fades continuously and causes up to 20% underestimation of IRSL ED values for samples with quartz OSL ages of 30 ～ 70ka. This gave us the first cognition about the anomalous fading process happened in natural way with geological period from 15ka to 70ka. The preliminary result about IRSL fading during the Last Glacial loess samples would be helpful to find a way which redress the effect of anomalous fading in dating application and also in understanding its mechanism.
出处
《第四纪研究》
CAS
CSCD
北大核心
2007年第4期553-558,共6页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:40602020)资助
关键词
洛川黄土
混合矿物
红外释光信号
热作用
异常衰减
Luochuan loess, polymineral grains, IRSL signal, thermal treatment, anomalous fading
