刘海金^1,,
龚志军^1,2,,,
罗明¹,
彭花明¹,
郭福生¹,
钟宝元¹
1. 东华理工大学地球科学学院, 江西 南昌 330013
2. 中国科学院地球环境研究所, 黄土与第四纪地质国家重点实验室, 陕西 西安 710061

基金项目: 国家自然科学基金地区科学基金项目（批准号：42062013）、江西省教育厅科学技术研究资助项目（批准号：GJJ160573）、江西省高等学校教学改革研究省级课题（批准号：JXJG-18-6-2）、中国科学院地球环境研究所黄土与第四纪地质国家重点实验室开放基金项目（批准号：SKLLQG1906）和东华理工大学核资源与环境重点实验室开放基金项目（批准号：NRE1607和2020Z01）共同资助


详细信息

作者简介: 刘海金, 男, 23岁, 硕士研究生, 第四纪地质与释光年代学专业, E-mail:lhjnsxw@163.com

通讯作者: 龚志军, E-mail:13697082584@163.com

中图分类号: P534.63;P597⁺.3

收稿日期:2020-02-22
修回日期:2020-05-09
刊出日期:2021-01-30

Study the effect of the water content and its error on the precision of optical age results for sediments

LIU Haijin^1,,
GONG Zhijun^1,2,,,
LUO Ming¹,
PENG Huaming¹,
GUO Fusheng¹,
ZHONG Baoyuan¹
1. School of Earth Sciences, East China University of Technology, Nanchang 330013, Jiangxi
2. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, Shaanxi


More Information

Corresponding author: GONG Zhijun,E-mail:13697082584@163.com

MSC: P534.63;P597⁺.3

--> Received Date: 22 February 2020
Revised Date: 09 May 2020
Publish Date: 30 January 2021


摘要
摘要:光释光测年技术是晚第四纪碎屑沉积物沉积年代测定方法之一。本研究关注沉积物样品含水量及其误差的选取对光释光测年精度的影响。从已发表相关文献选取4个光释光样品，其类型包含黄土、河流砂、砂质土壤等。一方面对这些样品含水量及其误差重新赋予不同值，另一方面对环境剂量率其他参数进行固定，之后重新计算这些样品光释光年代及观察对应误差棒变化。模拟结果表明：对于低含水量（≤6%）样品，含水量相对误差的选取几乎不改变光释光年龄误差棒大小；而对于中等含水量（约11%）样品，随着含水量相对误差从5%增加到50%，石英光释光年龄的相对误差增加约1%；对于较高含水量（16%~26%）样品，随着含水量相对误差从5%增加到50%，光释光年龄结果的相对误差增加0.9%~3.9%。之后利用兰州天斧沙宫附近的一个典型黄土样品，在实验室环境下模拟不同降雨组合，测量并计算该样品的年平均含水量及相对误差，实验模拟结果表明黄土样品无论在简单降雨模式还是复杂降雨模式下，黄土样品年平均含水量不超过15%，而含水量的相对误差不超过11%。该模拟实验结果进一步证实了释光测年研究中，含水量及误差经验赋值的可行性，为黄土高原地区黄土样品晚第四纪地质历史时期的水含量及误差估计提供了进一步实验室数据支持。
关键词: 光释光测年/
含水量/
晚第四纪/
年剂量率/
黄土

Abstract:Optical dating has been widely applied to Late Quaternary sediments in order to obtain their depositional ages. In this study, we focus on the effect of water content and its error on the precision of optical age results. Four OSL samples(loess, fluvial sand and sandy soil) with different annual external dose rates from 1 Gy/ka to 5 Gy/ka were selected from published literature. By assigning different water content value, different relative error of water content as well as fixing other relevant annual dose rate parameters, we monitored the corresponding OSL ages and the age error bar of these OSL samples. For quartz OSL samples, it is found that the relative error of water content has different impact on the OSL age error. When the water content was not more than 6%, the assigned different relative error of water content caused little change for the quartz OSL age error bar. However, when the water content value of quartz samples was not less than 11%, the relative error of quartz OSL age can increase more than 1.0%, as the relative error of water content increased from 5% to 50%. In addition, the water content value has significant impact on the final quartz OSL age determination. For example, for the quartz sample of HSDK-7, as the assigned water content increased from 1% to 6%, 11%, 16%, 21%, 26% in sequence, the corresponding quartz OSL age increased by 5.7%, 5.4%, 5.0%, 4.8%, 4.5% respectively. For K-feldspar grains, if both internal dose rate and external dose rate were used to calculate optical age, the corresponding K-feldspar OSL age error bar will be less affected by the water content, compared with quartz sample. When the water content was less than 11%, the assigning different relative error of water content caused little change for the K-feldspar optical age error bar. However, when the water content of K-feldspar samples was not less than 16%, the relative error of K-feldspar OSL age can increase more than 0.9%, as the relative error of water content increase from 5% to 50%. In addition, the water content value also has significant impact on the final K-feldspar OSL age determination. For example, for the K-feldspar sample of HSDK-7, as the assigned water content increased from 1% to 6%, 11%, 16%, 21%, 26% in sequence, the corresponding K-feldspar OSL age increased by 4.5%, 3.9%, 3.7%, 3.4%, 3.4% respectively. The results suggest that, for some samples with low water content(≤6%, e.g. sand sample in arid environment), the determination of relative error of water content has very limited effect on the precision of both quartz and K-feldspar optical ages. For samples with middle water content(ca.11%, e.g. loess samples in Chinese Loess Plateau), the relative error of water content has certain effect on the precision of quartz OSL age, while the it has much less effect on the precision of K-feldspar OSL age. For samples with relative high water content(between 16% and 26%), the relative error of water content has certain effect on the precision of both quartz OSL age and K-feldspar OSL age. Then, the annual average water content and relative error of a typical loess sample was simulated and tested with different rainfall combinations in the laboratory. The experimental simulation results show that the annual average water content of the loess sample was constrained between 4% and 9% and its relative error was constrained between 8% and 11% in simple rainfall model. Under complex rainfall mode, the annual average water content of the loess sample is then constrained between 8% and 15% and its relative error was constrained between 5.5% and 7.5%. In sum, the experimental simulation results suggest that the annual average water content of the loess sample is not more than 15% and the relative error of the water content is not more than 11% no matter in simple rainfall mode or complex rainfall mode. The simulation results further confirm the feasibility of empirical evaluation of water content and its error in the luminescence dating research, and provide further laboratory data for the water content and its error estimation for Late Quaternary loess samples from Chinese Loess Plateau.
Key words:optical dating/
water content/
Late Quaternary/
annual dose rate/
loess



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