青藏高原东缘湖相沉积和黄土高原黄土沉积磁化率与粒度相关性对比*

为探讨构造稳定地区(如黄土高原)和构造活跃地区(如青藏高原东缘)粉尘沉积物中磁化率(SUS)与粒度的相关性及其对环境事件的指示意义,本次研究分析了黄土高原蓝田剖面黄土—古土壤样品和青藏高原东缘湖相沉积样品的粒度和磁化率记录。黄土高原黄土—古土壤沉积SUS与2~10 μm粒度组分最强正相关,青藏高原东缘湖相沉积的SUS与2~10 μm粒度组分最强负相关,反映2~10 μm粒度组分为黄土高原和青藏高原乃至亚洲干旱—半干旱地区连续稳定敏感的背景沉积组分。黄土高原黄土—古土壤沉积的SUS与32~63 μm粒度组分最强负相关,青藏高原东缘湖相沉积的SUS与32~63 μm粒度组分最强正相关,反映32~63 μm粒度组分不仅是黄土高原尘暴事件沉积的敏感指标,也是青藏高原东缘湖相沉积记录的地震事件敏感指标。SUS与粒度组分的相关性在青藏高原东缘地区地震事件层开始部分高于结束部分,也较好地反映地震事件为研究区添加新鲜沉积物后随地形地貌恢复逐步减少的过程。SUS与粒度组分相关性也受当地物源的影响。

Comparison of correlation between magnetic susceptibility and grain size for lacustrine sediments in eastern Tibetan Plateau and loess deposits in Chinese Loess Plateau

To explore the correlation between magnetic susceptibility(SUS)and grain size of the dust deposits from the tectonically stable and active regions and its implications for environmental events,the grain size and SUS records from the Lantian loess sediments-paleosol of the Chinese Loess Plateau(CLP)were analyzed and compared with that of the lacustrine sediments from the eastern margin of the Tibetan Plateau(TP). Results indicate that the SUS of the loess sediments has the strongest positive correlation with the loess sediments of 2~10 μm grain size in the Chinese Loess Plateau(CLP) and strongest negative in the Tibetan Plateau,respectively,indicating that the 2~10 μm grain size of dust sediments were continuous and stable,which were deposited in the background of the arid to semi-arid regions in the CLP and TP and even in Asia. On the other hand,SUS showed the strongest positive correlation with the 32~63 μm grain size of the loess sediments in the Tibetan Plateau and strongest negative in the Chinese Loess Plateau(CLP),respectively,indicating that the 32~63 μm grain size of the dust sediments were the sensitive indicator not only for the dust storms in the CLP, but also for the seismic events in the eastern margin of the TP. The correlation between SUS and grain size during the beginning period of the seismic event in the eastern part of TP was higher than that of the ending period,indicating that the seismic event brings the fresh sediments in the study area and then decreases due to the gradual recovery of the landscape. The correlation between SUS and grain size is also influenced by the local provenance.