单颗粒释光测年技术及其在地质考古中的应用研究进展

近年来光释光测年在单颗粒技术上的研究取得了一系列重要进展,极大地提高了测年精度,为地质考古测年提供了更大的空间,研究者们对全球重要考古遗址点进行了详细的单颗粒测年,取得诸多考古新发现。单颗粒释光技术是在光释光单片技术上发展而来,对样品的单个石英或长石颗粒进行独立测试,基于单个颗粒测量结果,结合误差理论、统计学分析和样品地质沉积特征分析获得样品的准确年龄。本文结合大量地质考古样品的单颗粒测年数据,重点阐述了单颗粒释光测年技术的原理、发展历程、实验流程、筛选条件和年龄模型。单颗粒释光技术为地质考古的精确定年提供了可能性,尤其是对由于晒退不充分等原因导致的等效剂量分散的样品,如过度分散值(OD)高达20%甚至超过50%的地质考古样品,提供了新的方法和及时支持。通过开展释光测年信号分析,选择不同的单颗粒样品年龄模型分析,可以得到较为可靠的年龄,为诸多地质考古遗迹建立年代学框架。

A Review of Single-grain Optically Stimulated Luminescence Technology and Its Application in Geological Archaeology

BACKGROUND: In recent years, a series of important progressions has been made in the study of single-grain technology in optical stimulated luminescence (OSL) dating, which greatly improves the accuracy of dating and provides more space for geological and archaeological dating. A detailed single-grain dating has been carried out in globally important archaeological sites and many new archaeological discoveries have been made. The single-grain OSL technology is developed on the basis of photoluminescence monolithic technology. The single quartz or feldspar grains of the sample are independently tested, and the precise age of the sample is obtained based on the measurement results of a large number of grains, combined with error theory, statistical analysis and geological sedimentation characteristics.
OBJECTIVES: To understand the development process, experimental process and research difficulties of single-grain OSL technology.
METHODS: Equivalent dose (D_e) data were obtained by single-grain OSL dating protocol. Error theory and statistical principle were used for D_e value analyzing.
RESULTS: Single-grain OSL dating gets each grain''s signal for a sample to determine the D_e value for a sample, rather than the more conventional single-aliquot approach, which each aliquot consists of several 10-1000s of grains. This method was especially beneficial in archaeological contexts where:(1)An individual grain was the smallest fundamental unit for optical dating, providing detailed information on each grain for sample of interest. (2)Individual grains may respond differently even using the same machine under the same measurement conditions, while multi-grain aliquot cannot distinguish the grains suited to SAR procedure and the grains not, resulting that aliquots can be compromised by these ill-suited grains especially when they dominate the OSL signal. (3)Concerning about post-depositional disturbances, beta microdosimetry, possibility of roof spall contamination and non-homogeneous bleaching, these contaminant grains can be recognized by the distribution pattern of single-grain D_e values and be removed prior to age calculation. In order to get the exact D_e, there were 5 rejection and acceptation criteria and 4 age models. Some geological and archaeological samples had over dispersion value (OD) up to 20% or even more than 50% for dark samples. It is important to choose the right rejection and acceptation criteria and age model. This technology can provide new method and necessary support.
CONCLUSIONS: Single-grain OSL technology provided the possibility of precise geological archaeology, especially for samples with D_e dispersion due to insufficient bleaching. By carrying out single-grain OSL dating, choosing the right rejection and acceptation criteria and selecting different age models, a more reliable age can be obtained, avoiding wrong D_e. This method is suitable to establish a chronological framework for many geological and archaeological sites.