| 引用本文: | 唐响峰,王强,雷佳妹,贾佳,Khormali Farhad,Murodov Davlatkhudzha.2026.4μm粒级界限对伊朗黄土高原黄土成壤与碎屑磁性矿物判识的约束[J].地球环境学报,17(4):976-996 |
| TANG Xiangfeng,WANG Qiang,LEI Jiamei,JIA Jia,KHORMALI Farhad,MURODOV Davlatkhudzha.2026.Constraints of the 4 μm grain-size threshold on discriminating pedogenic and detrital magnetic minerals in loess from the Iranian Loess Plateau[J].Journal of Earth Environment,17(4):976-996 |
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| 4μm粒级界限对伊朗黄土高原黄土成壤与碎屑磁性矿物判识的约束 |
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唐响峰1，2，王强1，2，雷佳妹1，2，贾佳1，2，Khormali Farhad3，Murodov Davlatkhudzha4
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1.浙江师范大学 地理与环境科学学院，金华 321004 ；2.浙江师范大学 钱塘江流域地表过程与环境变化研究所，金华 321004 ；3.Department of Soil Science, Faculty of Water and Soil Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran ；4.Institute of Geology, Earthquake Engineering and Seismology of National Academy of Sciences of Tajikistan, Dushanbe, Tajikistan
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| 摘要: |
| 黄土磁性信号由风成碎屑输入与成壤改造共同控制，区分二者是利用环境磁学重建古气候的关键。已有中国黄土高原（CLP）研究提出4 μm可作为成壤与碎屑磁性矿物的粒级界限，但该界限在西风主控的亚洲中部干旱区西部是否适用仍缺乏检验。文章选取伊朗东北部伊朗黄土高原（ILP）沿显著降水梯度分布的34个现代表土样品，采用重力沉降-湿筛法分离＜4 μm、4—63 μm和＞63 μm组分，并对＜4 μm和4—63 μm组分开展系统环境磁学分析。结果显示，＜4 μm组分以细粒成壤亚铁磁性矿物为主，其频率磁化率（χfd）、非磁滞剩磁磁化率（χARM）及相关粒度敏感参数与年均降水显著正相关；4—63 μm组分虽以较粗PSD-MD颗粒为主，但其亚铁磁性参数同样与降水呈正相关，表明该组分含有不可忽略的成壤磁性矿物贡献。由此说明，在ILP，4 μm粒级界限不能有效分离成壤与碎屑来源磁性矿物，其适用性显著区别于季风主控的CLP。研究结果强调，黄土磁性矿物粒级分离界限具有区域依赖性，应结合物源、搬运、沉积和成壤过程建立适用于特定区域的环境磁学判识标准。 |
| 关键词: 伊朗黄土高原 现代表土 分粒级 磁性矿物 环境磁学 |
| DOI：10.7515/JEE2024090 |
| CSTR：32259.14.JEE2024090 |
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| 基金项目:国家自然科学基金项目（42101154） |
| 英文基金项目: |
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| Constraints of the 4 μm grain-size threshold on discriminating pedogenic and detrital magnetic minerals in loess from the Iranian Loess Plateau |
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TANG Xiangfeng1，2，WANG Qiang1，2，LEI Jiamei1，2，JIA Jia1，2，KHORMALI Farhad3，MURODOV Davlatkhudzha4
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1.College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua 321004 , China ；2.Institute of Surface Processes and Environmental Change in Qiantang River Basin, Zhejiang Normal University, Jinhua 321004 , China ；3.Department of Soil Science, Faculty of Water and Soil Engineering, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran ；4.Institute of Geology, Earthquake Engineering and Seismology of National Academy of Sciences of Tajikistan, Dushanbe, Tajikistan
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| Abstract: |
| Background, aim, and scope Environmental magnetism of loess has been widely used for reconstructing past climate variability, yet most studies rely on bulk samples, which obscure the respective contributions of pedogenic and detrital magnetic minerals and limit interpretation accuracy. Grain-size separation has been proposed as an effective approach to distinguish these components, and studies on the Chinese Loess Plateau (CLP) suggest that a 4-μm threshold may separate pedogenic and detrital fractions. However, this conclusion is largely based on monsoon-dominated regions and may not be universally applicable. The Iranian Loess Plateau (ILP), located in the western part of arid central Asia (ACA) under the influence of the mid-latitude westerlies, remains poorly studied in this regard. The ILP is characterized by extensive and relatively continuous loess deposits, a pronounced precipitation gradient, minimal temperature variation, and a Mediterranean-like climate distinct from the East Asian monsoon system. These features provide an ideal natural setting for isolating precipitation-driven processes. This study aims to evaluate the applicability of the 4 μm grain-size threshold for separating pedogenic and detrital magnetic minerals in ILP loess and to assess whether relationships established in the CLP are transferable to westerlies-dominated regions. Materials and methods A total of 34 representative modern surface soil samples were collected across the ILP along a well-defined precipitation gradient to ensure broad spatial coverage. Samples were pretreated and separated into three grain-size fractions (＜4 μm, 4—63 μm, and ＞63 μm) using a combination of gravitational settling (pipette method) and wet sieving. The ＜4 μm and 4—63 μm fractions were selected for detailed analysis. Environmental magnetic measurements, including magnetic susceptibility (χ), frequency-dependent susceptibility (χfd), anhysteretic remanent magnetization (ARM), isothermal remanent magnetization (IRM), and relative parameters, were conducted to characterize magnetic concentration, grain size, and domain states. Statistical analyses were performed to examine relationships between magnetic parameters and precipitation gradients. Results The two fractions show distinct but overlapping magnetic characteristics. The ＜4 μm fraction is dominated by stable single-domain (SSD) particles, indicating a strong pedogenic signature, whereas the 4—63 μm fraction is mainly composed of multi-domain (MD) and pseudo-single-domain (PSD) particles, with a minor SSD contribution. Ferrimagnetic parameters of both fractions exhibit significant positive correlations with precipitation, although correlations are stronger in the ＜4 μm fraction, suggesting higher climatic sensitivity of fine-grained pedogenic particles. Magnetic parameters in both fractions also increase with distance from the northernmost sampling sites, reflecting spatial environmental gradients. Notably, the 4—63 μm fraction contains a substantial pedogenic magnetic component, which significantly contributes to its overall magnetic properties, indicating that this fraction is not purely detrital. Discussion The results demonstrate that the 4 μm threshold does not effectively separate pedogenic and detrital magnetic minerals in the ILP, in contrast to findings from the CLP. This discrepancy highlights strong regional variability in loess magnetic properties. The incomplete separation likely results from differences in sediment sources, transport processes, wind dynamics, depositional environments, and post-depositional pedogenesis. In the westerlies-dominated ILP, pedogenic magnetic minerals may form and be preserved across a broader grain-size range, leading to overlap between fractions. Furthermore, the coexistence of SSD particles within the 4—63 μm fraction suggests that pedogenic processes are not restricted to fine particles, challenging the assumption that grain size alone can reliably distinguish magnetic mineral origins. These findings emphasize the need for region-specific interpretations of loess magnetic records. Conclusions In the ILP of western ACA, the commonly used 4 μm grain-size boundary cannot effectively distinguish pedogenic and detrital magnetic minerals. The presence of pedogenic components within the 4—63 μm fraction results in significant overlap and undermines the validity of this threshold in westerlies-dominated environments. This study reveals clear differences between ILP and CLP loess, highlighting the strong regional dependence of grain-size-magnetism relationships. Recommendations and perspectives Future studies should adopt region-specific approaches when applying grain-size separation methods in loess research. It is essential to consider geographic setting, atmospheric circulation, sediment sources, transport pathways, depositional conditions, and post-depositional processes. Statistically robust and controlled experiments are required to establish reliable grain-size thresholds tailored to specific regions. Integrating environmental magnetism with complementary proxies, such as geochemistry and mineralogy, will further improve the discrimination between pedogenic and detrital components and enhance the reliability of paleoclimate reconstructions. |
| Key words: Iranian Loess Plateau modern surface soil particle separation magnetic minerals environmental magnetism |
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