Occurrence and Distribution Patterns of Magnetic Particles Within Stalagmite Growth Laminae
Occurrence and Distribution Patterns of Magnetic Particles Within Stalagmite Growth Laminae
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DOI：
10.1029/2022gc010487
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发表时间：
2022-08
期刊：
影响因子：
3.7
通讯作者：
Taiheng Shi;Jianyv Ding;Zongmin Zhu;Hongbin Zhang;Junhua Huang
中科院分区：
文献类型：
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作者：
Taiheng Shi;Jianyv Ding;Zongmin Zhu;Hongbin Zhang;Junhua Huang
石笋中磁性颗粒的浓度与区域水文条件有很大关系，因此可以作为古气候重建的重要指标。通常选择石笋的中轴线区域进行磁性研究。然而，外生磁性颗粒在生长层中的分布及其影响因素尚不清楚。本文采用等温剩余磁化（IRM）采集曲线和低温磁性分析等磁性测量方法，研究了三种形状石笋生长层中磁性颗粒的分布及其变化规律。结果表明：剩磁载体主要为碎屑磁铁矿/磁赤铁矿，与少量赤铁矿、针铁矿共存；软磁性颗粒沿生长层的分布在三种形状石笋（穹状、锥状和烛状）中表现出不同的分布规律。对于圆顶状石笋，各生长层的软磁颗粒浓度均呈现由中心向边缘递增的趋势。在锥状石笋和烛状石笋的底部生长层也出现了类似的图案。这种磁颗粒边缘富集是由水滴洗涤作用引起的。然而，这种富集模式在锥状和烛状石笋的顶部生长层中变得较弱甚至相反，这表明石笋的形状也会影响软磁矿物的表面分布。磁性颗粒的不均匀分布意味着石笋的中轴线区域可能并不总是环境磁性研究的最佳样本。
The concentrations of magnetic particles in stalagmites depend greatly on the regional hydrologic condition, and thus can act as an important proxy for paleoclimate reconstruction. The central axis region of a stalagmite is usually selected for such magnetism study. However, little is known about the distribution and influence factors of exogenetic magnetic particles within the growth laminae. In this study, the occurrence and variations of magnetic particles along the growth laminae of three shape stalagmites were investigated by a set of magnetic measurements, including isothermal remanent magnetization (IRM) acquisition curves and low‐temperature magnetic analysis. The results show the main magnetic remanence carrier is detrital magnetite/maghemite, coexisting with small amounts of hematite and goethite. The distribution of soft magnetic particles along the growth laminae showed different patterns among the three shape stalagmites (dome, cone, and candle). For the dome shape stalagmite, the soft magnetic particle concentrations in all studied growth layers showed an increasing trend from center to edge. Similar patterns were also appeared in the bottom growth layers of the cone and candle shape stalagmites. This edge enrichment of magnetic particles is caused by drip water washing effect. However, such enrichment pattern became weaker or even inverse in the top growth layers of the cone and candle shape stalagmites, indicating that the shapes of stalagmites could also affect the surface distribution of soft magnetic minerals. These uneven distributions of magnetic particles imply that the central axis region of a stalagmite may not always be the optimal specimen for environmental magnetism study.