任翌成^1,,
李徐生¹,
韩志勇^1,,,
陈英勇^1,2,
汪雨辰¹,
刘梦慧¹,
潘柔娴¹,
鹿化煜¹
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

基金项目: 国家自然科学基金项目（41690111，41571188，41671191和40971004）资助


详细信息

作者简介: 任翌成, 男, 1995年生, 硕士研究生.主要从事地貌学方面的研究.E-mail:mg1727009@smail.nju.edu.cn

通讯作者: 韩志勇, 男, 1968年生, 主要从事地貌与第四纪环境、古气候方面的研究.E-mail:zyhan@nju.edu.cn

中图分类号: P318

收稿日期:2019-11-11
修回日期:2020-02-19
上线日期:2020-05-05

Chronological sequence of the Xiashu Loess based on the relative paleointensity of geomagnetic field and its implications

REN YiCheng^1,,
LI XuSheng¹,
HAN ZhiYong^1,,,
CHEN YingYong^1,2,
WANG YuChen¹,
LIU MengHui¹,
PAN RouXian¹,
LU HuaYu¹
1. School of Geography and Ocean Science, Nanjing University, Nanjing 210093, China
2. College of Environment and Planning, Henan University, Kaifeng Henan 475001, China


More Information

Corresponding author: HAN ZhiYong,E-mail:zyhan@nju.edu.cn

MSC: P318

--> Received Date: 11 November 2019
Revised Date: 19 February 2020
Available Online: 05 May 2020


摘要
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（χ）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（819~700 ka）对应中更新世转型阶段，东亚季风降水较少.阶段Ⅲ（700~412 ka）对应中更新世的大间冰期，东亚季风降水最多.阶段Ⅱ（412~197 ka）时东亚季风降水减少，较阶段Ⅳ略少.阶段Ⅰ（197~34 ka）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.
关键词: 下蜀黄土/
地磁场/
相对古强度/
年代标尺/
季风降水

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.
Key words:Xiashu Loess/
Geomagnetic field/
Relative paleointensity/
Time scale/
Monsoon precipitation



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