| 摘要: |
| 早—中更新世沉积年代的确定是第四纪研究领域亟待解决的难题，电子自旋共振（ESR）测年法为该时段沉积物定年提供了可能。但已有的研究发现：石英Ti心和Al心ESR信号完全衰退“回零”或达到较稳定“残留”所需时间较长，因而其可信性备受质疑。本研究选取腾格里沙漠白碱湖地区BJ14钻孔中5个不同深度的沉积物，分别基于其中石英Ti心和Al心信号进行了ESR定年。测年结果显示：（1）2个样品基于Al心ESR信号与基于Ti-Li心ESR信号的测年结果在年龄误差范围内一致，其它3个样品Al心ESR测年结果较Ti-Li心测年结果偏老200—500 ka；（2）与该孔的古地磁测年结果对比表明，石英Ti-Li心ESR测年结果相对可靠。上述研究结果表明石英Ti-Li心的ESR测年结果至少能提供中更新世更为可信的沉积年龄。 |
| 关键词: ESR测年 Al心 Ti-Li心 腾格里沙漠 |
| DOI：10.7515/JEE182051 |
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| 基金项目:国家自然科学基金项目（41772169）；中央高校基本科研业务费项目（Lzujbky-2018-it21） |
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| Comparison of the electron spin resonance (ESR) dating results between Al signals and Ti-Li signals in quartz grains: a case from sediments of BJ14 core drilled from the Baijian Lake in the Tengger Desert |
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LI Zhenjun, MOU Xuesong, FAN Yuxin
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1. Key Laboratory of Mineral Resources in Western China (Gansu Province), School of Earth Sciences, Lanzhou University, Lanzhou 730000, China
2. Key Laboratory of Western China’s Environmental Systems (Ministry of Education), Lanzhou University, Lanzhou 730000, China
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| Abstract: |
| Background, aim, and scope The determination of the depositional age of Early to Middle Pleistocene is an urgent problem for Quaternary studies, the ESR dating method provides the possibility for the dating of sediments during this period. However, previous works have found that it takes a long time for the signal associated with the titanium (Ti) and aluminum (Al) defects in detrital quartz grains to be reduced to zero or to constant residual value by sunlight exposure, which may cause the phenomenon that the ESR signals of quartz grains is incomplete bleaching prior to sediment deposition. On the other hand, when using ESR signal of quartz for dating, it is difficult to accurately determine whether the ESR signal has been reset to its constant residual value or to zero, moreover, the constant residual value of ESR signal for Al center is difficult to be estimated accurately. Therefore, the reliability by this method remains to be questioned. In this paper, we attempt to identify the best agreement between other age criteria established by paleomagnetic dating study with observed age and to determine whether ESR dating is reliable. Materials and methods Here we carried out ESR analyses on five samples with different depths from the BJ14 core drilled from the Baijian Lake in the present Tengger Desert based on Ti-Li signal and Al signal in detrital quartz grains. Results Our results show that: (1) this method yields agreement between the Al signal and Ti-Li signal ages for 2 samples, while Al signal ages were 200—500 ka older than Ti-Li signal ages for other 3 samples; (2) the dates obtained by this method based on Ti-Li signal are generally consistent with paleomagnetic dating results from BJ14 core and therefore appear to be reliable. Discussion The fact that the Al signal age is older than Ti-Li signal age is probably related to the previous recognition given Al center signal slower bleaching kinetics in comparison with the Ti center. In desert environment, the process of migration or accumulation for aeolian sand is rapid, for which ESR signal of Ti-Li center has been to reset to zero, while incomplete bleaching for ESR signal of Al center. Conclusions Finally, these results demonstrate that a great potential for using Ti-Li centres to date Early Pleistocene deposits, and the usefulness of using the multiple centres approach, here, although we only carried out ESR analyses based on two kinds of ESR signals (Ti-Li signal and Al signal) in detrital quartz grains. Meanwhile, we can infer that ESR optical age estimates to be reported as an accurate burial age based on Ti and Al signals should keep agreement between D e values for both the Al and Ti signals. And if there is no independent age control, we obtain disagreement between the ages obtained by the two signals, and furthermore the Al signal age is less than that from the Ti signal age, then the Ti signal age can probably be taken as the age of burial. Recommendations and perspectives Our results show that the ESR dating has the potential to date much older deposits, and the importance to measure both Al and Ti centers for dating purpose. We recommend that the MC approach (the multiple center) should be finally very most tested for dating purpose. |
| Key words: ESR dating Al center Ti-Li center Tengger Desert |
