| 摘要: |
| 本文以中国东北松原黄土为研究对象，通过光释光测年建立其末次冰期年代标尺，并探讨磁化率和平均粒径这两个黄土研究中常用的气候替代性指标的可能指示意义。采用成熟的细颗粒石英单片再生（SAR）光释光（OSL）测年技术获得了松原剖面顶部5.5 m年代6个，并获得了2 cm间距的低频磁化率和平均粒径这两个常规参数。石英OSL测年相关检验证实了该技术测量松原黄土的可靠性。测年结果表明，松原剖面顶部5.5 m主要沉积于末次冰期的中晚期，即约5.5 — 1.8 m（（52.18 ± 3.47） — （27.76 ±1.77） ka）主要堆积于深海氧同位素阶段（MIS）3中晚期，而顶部1.8 — 0.4 m（（27.76 ± 1.77） — （20.61±1.31） ka）堆积于MIS2早期。磁化率自52.18 ± 3.47 ka到27.76 ± 1.77 ka经历了先小幅降低又小幅升高，波动幅度较小，而自27.76 ± 1.77 ka以后，磁化率值呈整体下降并呈现大幅度摆动。平均粒径则自52.18 ± 3.47 ka到46.80 ± 3.13 ka呈明显变小趋势，自46.80 ± 3.13 ka到约20 ka变化不大，自约20 ka以后，平均粒径由约40 μm陡然增加至约140 μm，并在之后稳定在这一水平。测试结果对比显示，磁化率和粒度的变化不具有明显的相位关系，且同黄土高原渭南剖面末次冰期磁化率和平均粒径的变化也表现出明显的不一致现象。因此，在对松原黄土剖面的研究中，将磁化率和平均粒径分别作为东亚夏季风和冬季风的替代性指标使用时要慎重。 |
| 关键词: 松原黄土 末次冰期 石英光释光 磁化率 平均粒径 古气候 |
| DOI：10.7515/JEE201705003 |
| CSTR：32259.14.JEE201705003 |
| 分类号: |
| 基金项目:国家重大科学研究计划（2013CB955901）；国家自然科学基金项目（41290254）；国家重点研发计划（2016YFA0601902） |
| 英文基金项目:National Basic Research Program of China (2013CB955901); National Natural Science Foundation of China (41290254); National Key Research and Development Program of China (2016YFA0601902) |
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| Luminescence dating of the last glacial Songyuan loess in northeastern China and its paleoclimate significance: preliminary results |
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WANG Songna, WANG Xulong, KANG Shugang
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1. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
2. University of Chinese Academy of Sciences, Beijing 100049, China
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| Abstract: |
| Background, aim, and scope When compared with the robust paleoclimatic results on the Chinese Loess Plateau (CLP), there is still a lack of paleoclimatic research based on the loess in the northeastern China, and chronology and proxy are crucial for resolving above question. In this study, we tried to obtain the luminescence chronology of the last glacial Songyuan loess in northeastern China. Meanwhile, the possible significance of the often used proxy in loess research, magnetic susceptibility and mean grain size, is discussed. Materials and methods The fine-grained quartz single aliquot regenerative dose (SAR) optically stimulated luminescence (OSL) dating protocol is used for obtaining the six ages of the upper 5.5 m loess at Songyuan. Conventional tests in SAR protocol indicate the reliability of quartz OSL dating in this study. Meanwhile, the low frequency magnetic susceptibility and mean grain size are measured at 2 cm interval. Results Quartz OSL dating results show that, the upper 5 m loess mainly deposited during the middle-late Last Glacial. In detail, loess from depth of 5.5 m to 1.8 m ((52.18 ± 3.47) — (27.76 ± 1.77) ka) deposited during the middle-late marine isotope stage MIS3, and that from depth of 1.8 m to 0.4 m ((27.76 ± 1.77) — (20.61 ± 1.31) ka) accumulated during the early MIS2. Magnetic susceptibility shows a slightly decreasing trend from 52.18±3.47 ka to 46.80 ± 3.13 ka, then, slightly increases until 27.76 ± 1.77 ka. After 27.76 ± 1.77 ka, magnetic susceptibility decreases with abrupt secondary changes. There is an evident fining trend of Songyuan loess from 52.18 ± 3.47 ka to 46.80 ± 3.13 ka. Then, the mean grain size shows little changes until approximately 20 ka. After approximately 20 ka, the mean grain size dramatically increases from ~40 μm to ~140 μm, and finally it keeps at ~140 μm. Discussion It can be seen that changes of magnetic susceptibility and mean grain size are quite different and have not in-phase or anti-phased relationships at Songyuan, and, they are inconsistent with those at Weinan on the CLP. Conclusions Therefore, it is suggested that we should take caution to use magnetic susceptibility and mean grain size to as proxy of intensity of East Asian summer and winter monsoons respectively at Songyuan. Recommmendations and perspectives In the future, to understand the loess in northeastern China in detail, more efforts need to be put on the high-resolution and longer scale chronology construction. Also, the palaeoclimatic significance of some proxy (e.g. magnetic susceptibility, mean grain size) needs to be studied further. |
| Key words: Songyuan loess last glacial quartz optically stimulated luminescence magnetic susceptibility mean grain size paleoclimate |
