A STUDY ON PARTIAL ANHYSTERETIC REMANENCE IN SEDIMENTS FROM GANHAI LAKE, NINGWU TIANCHI
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摘要: 应用部分非磁滞剩磁（pARM）谱，对山西宁武天池干海湖泊沉积物携带的磁信息研究表明，粗磁铁矿颗粒（MD）是主要载磁矿物颗粒，其pARM谱在低矫顽力区间（AF < 20 mT）达到最高值；而细磁铁矿颗粒（PSD-SD）为次要载磁颗粒，其pARM谱在高矫顽力区间（AF>20 mT）稍有突起。但是，剖面三个层位具有不同特征，上层（大约7.3~4.0 ka）的粗磁性矿物颗粒含量最高，下层（大约12.0~13.0 ka）次之，而中层（大约12.0~7.3 ka）相对最低；中层的细磁性颗粒含量最高，下层和上层的细磁性颗粒含量次之。pARM谱分析结果与磁滞曲线测量获得的磁畴结果一致。在较高的交变磁场区间获得的pARM可以有效地压抑粗磁颗粒的信息，进而使细磁颗粒的信号增强。应用pARM谱分析，能有效判别样品中磁性矿物的磁畴状态，有助于沉积物的古气候、岩石磁学和古地磁学研究。Abstract: A study of partial anhysteretic remanent magnetization (pARM) spectra in samples from a sediment profile of Ganhai Lake (38°53'N, 112°11'E) shows variations in effective magnetic grain sizes of the lake sediment magnetite particles, consistent with the hysteresis results. Within the full profile, most magnetite particles are of coarse, multi-domain (MD) size, as shown by the dominant low coercivity (AF < 20 mT) spectra, with a few samples showing finer single domain (SD)-pseudo-single domain (PSD) particles with higher coercivity (AF>20 mT). The uppermost level (~7.3~4.0 ka) contains more coarse MD magnetite grains due to higher pARM peaks than the middle (~12.0~7.3 ka) and the lowermost level (~13.0~12.0 ka) that shows lower peaks. The middle level shows slight more fine SD-PSD magnetite grains than both the uppermost and lowermost level. High-field pARM spectrum can effectively identify fine PSD-SD magnetite grains and reduce effects of MD grains. Therefore, pARM spectrum analysis can be utilized to quickly and effectively determine the relative amount of fine magnetic grains in the samples, which is helpful to the study of the paleo-climate, rock magnetism and paleomagnetism of the lake sediments.
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Key words:
- pARM /
- magnetic grains /
- lake sediments /
- Ningwu /
- rock magnetism
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图 1 干海湖泊地质位置和全貌图[11]
Figure 1. Location and detail map of Ganhai Lake indicated by a blue circle
图 2 干海湖泊剖面上层沉积物样品的pARM谱变化规律
Figure 2. Variations in pARM spectra for samples from the uppermost level
图 3 干海湖泊剖面中层沉积物样品的pARM谱变化规律
Figure 3. Variations in pARM spectra for samples from the middle level
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