| 环境磁学视角下的北冰洋深海磁性地层：以罗蒙诺索夫脊ARC5-ICE4孔为例 |
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| 引用本文： | 张茂, 刘建兴, 邹庆超, 姚政权, 刘焱光, 石学法. 2023. 环境磁学视角下的北冰洋深海磁性地层：以罗蒙诺索夫脊ARC5-ICE4孔为例. 地球物理学报, 66(7): 2983-2996, doi: 10.6038/cjg2022Q0645 |
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| 作者姓名： | 张茂 刘建兴 邹庆超 姚政权 刘焱光 石学法 |
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| 作者单位： | 1. 自然资源部第一海洋研究所，海洋地质与成矿作用自然资源部重点实验室，山东青岛 266061; 2. 青岛海洋科学与技术试点国家实验室，海洋地质过程与环境功能实验室，山东青岛 266237 |
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| 基金项目： | 中央级公益性科研院所基本科研业务费专项资金(2021S01)；;国家自然科学基金(41876070)联合资助； |
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| 摘 要： | 近年来，北冰洋深海百万年尺度的磁性地层年代框架受到了来自诸如Mn旋回地层和钛磁赤铁矿“自反转”现象的强烈质疑，以致对该方法在北冰洋的适用性产生了巨大争议.鉴于此，本文对中国第五次北极科学考察在北冰洋罗蒙诺索夫海岭获得的ARC5-ICE4钻孔岩心(水深2860 m，进尺4.15 m)开展了深入的岩石磁学分析.结果证实岩心中的载磁组分以磁铁矿为主，部分颗粒表面发生轻微氧化作用，另含少量磁赤铁矿、赤铁矿、钛磁赤铁矿等；整体粒径呈现相对均一的准单畴(PSD：pseudo-single domain)，且含量随深度变化不大.岩心1.15~2.04 m区间显示的负极性并非“自反转”所致，而是真实的古地磁场记录；结合相对古强度(RPI)曲线模式和S-ratio的旋回变化特征，将其对应于松山期(约2.58~0.78 Ma)，钻孔底界年龄 < 3.58 Ma.另外，上述年代框架指示的沉积速率变化模式很好地吻合了北半球冰期加强(iNHG：intensification of Northern Hemisphere glaciation)和中更新世气候转型(MPT：mid-Pleistocene transition)等古气候事件，更加印证了其可靠性.因此，即使“自反转”现象在北冰洋深海地区真实存在，其影响范围也是局部的，即磁性地层对于建立该区新生代年代框架的重要性仍不容忽视.总之，目前北冰洋深海沉积物定年仍面临诸多难题和挑战，今后需加强多学科协作.
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| 关 键 词： | 北冰洋深海沉积 岩石磁学 相对古强度 磁性地层 自反转 |
| 收稿时间： | 2022-08-12 |
| 修稿时间： | 2023-02-03 |
Verification of the Arctic deep-sea magnetostratigraphy in enviromagnetic perspectives: A case study for sediment core ARC5-ICE4 on the Lomonosov Ridge |
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| ZHANG Mao, LIU JianXing, ZOU QingChao, YAO ZhengQuan, LIU YanGuang, SHI XueFa. 2023. Verification of the Arctic deep-sea magnetostratigraphy in enviromagnetic perspectives: A case study for sediment core ARC5-ICE4 on the Lomonosov Ridge. Chinese Journal of Geophysics (in Chinese), 66(7): 2983-2996, doi: 10.6038/cjg2022Q0645 |
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| Authors: | ZHANG Mao LIU JianXing ZOU QingChao YAO ZhengQuan LIU YanGuang SHI XueFa |
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| Affiliation: | 1. Key Laboratory of Marine Geology and Metallogeny, First Institute of Oceanography, Ministry of Natural Resources (MNR), Qingdao Shandong 266061, China; 2. Laboratory for Marine Geology, Pilot National Laboratory for Marine Science and Technology, Qingdao Shandong 266237, China |
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| Abstract: | The million-year-scale magnetostratigraphic chronologies of the deep-sea Arctic Ocean has been vigorously challenged by such as the Mn-cyclicity stratigraphy and titanomaghemite "self-reversal" in recent years. This has led to a huge controversy among researchers over the applicability of magnetostratigraphy to the Arctic Ocean. In view of this, rock magnetic analyses were conducted on a 4.15-m-long sediment core (ARC5-ICE4) that was obtained on the Lomonosov Ridge of the Arctic Ocean, at a water depth of 2860 m, during the 5th Chinese National Arctic Research Expedition. The results confirm that magnetic components in the studied sediments are dominated by magnetite, with a small quantity of maghemite, hematite, titanomaghemite, etc., and part of these magnetic particles was subjected to slight surface oxidation. The identified magnetic minerals exhibit relatively homogeneous pseudo-single domain (PSD) characteristics as a whole, and the variation in magnetic content along depths is also restrained. The negative polarities spanning the 1.15~2.04 m interval (R1) are not resulted from "self-reversal", but from the authentic records of the paleomagnetic field. These facts, coupled with the relative paleointensity (RPI) model and cyclicity of S-ratio value, correspond R1 to the Matuyama Chron (about 2.58~0.78 Ma), extrapolating a basal age of < 3.58 Ma. Moreover, the constructed chronology yields changing patterns of sedimentation rate agreeing well with the mid-Pleistocene transition (MPT) and intensification of Northern Hemisphere glaciation (iNHG), which authenticates further its fidelity. Therefore, even if the "self-reversal" phenomenon really exists in the deep-sea region of the Arctic, its scope of influence is still local. In other words, the importance of magnetostratigraphy in establishing the Cenozoic chronology of the region cannot be ignored. In brief, there are still a good many difficulties and challenges in dating the Arctic deep-sea sediments, which deserves further multidisciplinary cooperation in the future. |
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| Keywords: | Deep-sea sediments of the Arctic Ocean Rock magnetism Relative paleointensity Magnetostratigraphy Self-reversal |
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