| 引用本文: | 赵秋月，臧凯旋，彭淑贞，周锐，范念念，丁敏，方慜，吉春雯.2022.末次冰期以来青州黄土光释光测年及其对古气候的指示[J].地球环境学报,13(3):281-295 |
| ZHAO Qiuyue, ZANG Kaixuan, PENG Shuzhen, ZHOU Rui, FAN Niannian, DING Min, FANG Min,
JI Chunwen.2022.Optically stimulated luminescence dating of Qingzhou loess since the last glacial period and its climatic implications[J].Journal of Earth Environment,13(3):281-295 |
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| 摘要: |
| 黄河下游湿润-半湿润地区的鲁中黄土-古土壤沉积，是记录东亚季风气候变化的良好载体。山东青州邵庄黄土剖面粗颗粒石英（63—90 µm）光释光年代和磁化率、粒度、色度以及主量元素测试结果表明：（1）邵庄黄土末次冰期以来（(51.3±2.5)— (8.1±1.1) ka）沉积连续；（2）与粒度、磁化率和色度指标相比，化学蚀变指数能够更灵敏地反映冰期-间冰期沉积旋回；（3）粒度结果表明“古土壤”层中值粒径（16.9—24.6 μm）明显高于下伏黄土层中值粒径（11.8—22.7 μm），主要是因为近源沉积在总的沉积通量中所占比例在冰期-间冰期尺度上的变化；（4）灰黑色“古土壤”层底界年龄为(19.1±1.6) ka，明显老于黄土高原全新世古土壤层底界年代（约10—11 ka），其既包含全新世沉积的加积型土壤，也包含下伏末次冰期黄土层基础上受风化、淋溶形成的非加积型土壤。虽然研究区的“古土壤”包含非加积型土壤，记录了间冰期风化成壤过程，但依然能够反映冰期-间冰期气候旋回，是东亚乃至全球气候变化的产物。 |
| 关键词: 光释光测年 古土壤 古气候 邵庄黄土 化学蚀变指数 |
| DOI：10.7515/JEE222006 |
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| 基金项目:山东省自然科学基金项目（ZR2021MD008）；国家自然科学基金项目（41602353，41888101）；黄土与第四纪地质国家重点实验室开放基金（SKLLQG2134）；中国地震局地震预测研究所基本科研业务费专项（2019IEF0505） |
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| Optically stimulated luminescence dating of Qingzhou loess since the last glacial period and its climatic implications |
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ZHAO Qiuyue, ZANG Kaixuan, PENG Shuzhen, ZHOU Rui, FAN Niannian, DING Min, FANG Min,
JI Chunwen
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1. Tourism College, Taishan University, Tai’an 271000, China
2. College of Life Science, Yan’an University, Yan’an 716000, China
3. Institute of Earthquake Forecasting, China Earthquake Administration, Beijing 100036, China
4. State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource & Hydropower, Sichuan University, Chengdu 610065, China
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| Abstract: |
| Background, aim, and scope Distributed in the humid and semihumid area in the lower reaches of the Yellow River, loess-palaeosol deposits of central Shandong Province are important for studying the palaeoenvironmental evolution of alluvial plains in eastern China. The loess in the Central Shandong Mountains contains many loess-palaeosol cycles, which have great significance for reconstructing long-term regional palaeoclimate changes. However, compared to the wide attention given to the loess layers, fewer studies have explored the palaeosols recording the processes and characteristics of interglacial climate variations. The aim of our study is to determine the absolute ages and obtain the genesis and climate implications for the Holocene palaeosol. OSL, grain sizes, magnetic susceptibility and chroma samples were taken from the Shaozhuang loess sections in Qingzhou, Shandong Province. Materials and methods The coarse (63—90 µm) quartz OSL single aliquot regenerative (SAR) dose protocol was utilized to obtain the equivalent dose (D e). The preheating temperature was 260℃, and 220℃ was the cut-heat temperature. These conditions were suitable for all quartz D e measurements supported by the preheat plateau and dose recovery tests. Environmental dose rates were acquired using inductively coupled plasma mass spectrometry (ICP-MS) for the contents of U and Th and atomic absorption spectroscopy (AAS) for the content of K. The grain sizes, magnetic susceptibility and chroma (lightness, redness and yellowness) were measured at 2.5 cm intervals, and the major elements were determined at 10 cm intervals. Results The equivalent dose distribution of 22 samples from the Shaozhuang section is approximately 137.02—22.82 Gy, and the dose rate ranges from 2.55—3.18 Gy·ka−1. According to these values, the OSL ages can be acquired. Quartz OSL ages indicate that the section was deposited between 51.3 ka and 8.1 ka, with sedimentation rates fluctuating rapidly. The results of magnetic susceptibility and chroma are consistent with the stratigraphy in the field. However, the index of grain sizes and CIA values are slightly different from the loess-palaeosol cycles identified in the field. Discussion The loess grain size in the last glacial period was smaller than that of the palaeosol in the study area, which was mainly attributed to the contribution of less-distant dense vegetation in the warmer and wetter climate during summer in the interglacial period. Moreover, during winter in the interglacial period, the sediments transported by the Yellow River provided increased material for the deposition of local palaeosols, and the contribution of locally sourced deposits was greater in the humid and semihumid regions, resulting in the lower 5—16 µm particle percentage and higher 63 µm median particle size percentage. Furthermore, the sedimentation rate of the “palaeosol layer” indicated by chroma is about 10.6 cm·ka−1 (116 cm deposited at 19—8 ka), which is also slightly higher than the deposition rate of the underlying loess layer of about 6.0 cm·ka−1 (160 cm deposited at 47—19 ka). Although the CIA values for the 19—14 ka period are significantly lower than those for the early Middle Holocene (about 14—8 ka), they are mainly due to lower temperature and less precipitation during 19—14 ka. Conclusions (1) Loess-palaeosol sequences generally show a continuous trend of deposition over the last glacial period ((51.3±2.5)— (8.1±1.1) ka) in the Shaozhuang section. (2) The CIA is sensitive to the cycles of glacial-interglacial sedimentation. (3) The grain size results show that the median grain sizes of the “palaeosol layer” (16.9—24.6 μm) are obviously higher than those of the underlying loess layer (11.8—22.7 μm), mainly due to the variations in the proportion of local source sedimentation in the total sedimentation fluxes on the glacial-interglacial scale. (4) According to the OSL ages corresponding to the changes in chroma and CIA values, the middle and upper parts (about 14—8 ka) of the “palaeosol” layer are aggraded soils, and the middle and lower parts (about 19—14 ka) are nonaggraded soils formed by the weathering of glacial loess under the warm and humid climate of the Holocene. Recommendations and perspectives Although the “palaeosol” in the study area contains nonaggraded soil that records weathering and pedogenesis processes in the interglacial period, it still reflects glacial-interglacial cycles, which are the product of East Asian and even global climatic variations. |
| Key words: optically stimulated luminescence dating palaeosol palaeoclimate Shaozhuang loess chemical
index of alteration |
