| 基于地磁场相对古强度变化的下蜀黄土年代序列及其古气候意义 |
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| 引用本文： | 任翌成,李徐生,韩志勇,陈英勇,汪雨辰,刘梦慧,潘柔娴,鹿化煜.基于地磁场相对古强度变化的下蜀黄土年代序列及其古气候意义[J].地球物理学报,2020,63(5):2024-2035. |
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| 作者姓名： | 任翌成 李徐生 韩志勇 陈英勇 汪雨辰 刘梦慧 潘柔娴 鹿化煜 |
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| 作者单位： | 1. 南京大学地理与海洋科学学院, 南京 210093;2. 河南大学环境与规划学院, 开封 475001 |
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| 基金项目： | 国家自然科学基金项目（41690111，41571188，41671191和40971004）资助. |
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| 摘 要： | 分布于宁镇地区的下蜀黄土年代标尺研究薄弱.我们以镇江大港钻孔岩芯的下蜀黄土为例,探讨了下蜀黄土记录地磁场相对古强度的可靠性.岩石磁学的实验显示,下蜀黄土大体上符合估计相对古强度对沉积物的要求.以低频磁化率()作为天然剩磁(NRM300)的归一化因子,我们获得了下蜀黄土记录的地磁场相对古强度变化.通过与邻区和全球的单个及合成曲线的对比,我们发现大港钻孔岩芯的相对古强度记录展现出主要的全球偶极场的变化特征,因而可用于建立下蜀黄土的年代标尺.新的年代标尺表明,大港钻孔的磁化率年代序列与北方黄土无法直接对比,证实了该地点的下蜀黄土磁化率变化机制与北方的不同.大港钻孔下蜀黄土的沉积速率与磁化率相关,低风尘沉积速率对应低磁化率,是降水增加所导致的结果.沉积速率与磁化率年代序列显示,下蜀黄土记录的本区季风变化过程可分为4个阶段.阶段Ⅳ(819～700ka)对应中更新世转型阶段,东亚季风降水较少.阶段Ⅲ(700～412ka)对应中更新世的大间冰期,东亚季风降水最多.阶段Ⅱ(412～197ka)时东亚季风降水减少,较阶段Ⅳ略少.阶段Ⅰ(197～34ka)东亚季风降水最少.因此,中更新世气候转型后,长时间尺度东亚季风降水持续减少,可能受全球温度阶段性降低驱动.
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| 关 键 词： | 下蜀黄土 地磁场 相对古强度 年代标尺 季风降水 |
| 收稿时间： | 2019-11-11 |
Chronological sequence of the Xiashu Loess based on the relative paleointensity of geomagnetic field and its implications |
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| REN YiCheng,LI XuSheng,HAN ZhiYong,CHEN YingYong,WANG YuChen,LIU MengHui,PAN RouXian,LU HuaYu.Chronological sequence of the Xiashu Loess based on the relative paleointensity of geomagnetic field and its implications[J].Chinese Journal of Geophysics,2020,63(5):2024-2035. |
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| Authors: | REN YiCheng LI XuSheng HAN ZhiYong CHEN YingYong WANG YuChen LIU MengHui PAN RouXian LU HuaYu |
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| Institution: | 1. School of Geography and Ocean Science, Nanjing University, Nanjing 210093, China;2. College of Environment and Planning, Henan University, Kaifeng Henan 475001, China |
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| Abstract: | The Xiashu Loess distributed in the region from Nanjing to Zhenjiang is lack of a reliable time scale. Taking a drilling core at Zhenjiang as an example, we discuss the reliability of the reconstructed relative paleointensity of geomagnetic field in the Xiashu Loess. Rock magnetic experiments show that the Xiashu Loess approximately meets the requirements for reconstruction of the relative paleointensity in sediments. Using the low-field susceptibility (χ) to normalize the natural remanence (NRM300) after being thermally demagnetized at 300℃, we obtain the record of the relative paleointensity variation in the Xiashu Loess. Comparing with the single or synthesized curves both in neighboring regions and in the world, we find that the relative paleointensity in the Xiashu Loess exhibits main characteristics of the global dipole field, which can be used to establish the time scale. The obtained time scale shows that the chronological sequence of magnetic susceptibility of the Xiashu Loess cannot be correlated to that of loess in north China, which demonstrates the change mechanism of magnetic susceptibility differs from one another. The sedimentation rate is relevant to magnetic susceptibility in the Xiashu Loess. The low sedimentation rate corresponds to the low magnetic susceptibility, which results from the increased precipitation. Both the sedimentation rate and the magnetic susceptibility reveal that the paleoclimate change can be divided into four stages. The precipitation of the East Asian monsoon was low at Stage Ⅳ (819~700 ka) which is roughly correlated to the Middle Pleistocene Transition (MPT). The precipitation increased at Stage Ⅲ (700~412 ka) which is roughly correlated to the Great Interglacial. The monsoon precipitation decreased at Stage Ⅱ (412~197 ka) and probably was lower than that at Stage Ⅳ. The monsoon precipitation decreased to the lowest level at Stage Ⅰ (197~34 ka). In general, the precipitation of East Asian monsoon continued to decrease since the MPT and the aridification was gradually strengthened in this region. |
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| Keywords: | Xiashu Loess Geomagnetic field Relative paleointensity Time scale Monsoon precipitation |
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