摘要
在黄土高原-阿拉善高原区域沿接近降水量最大梯度线方向系统采集了表土(包括沙漠和土壤)样品,详细研究了其环境磁学、粒度和有机质含量等环境替代指标的变化特征。结果表明,整个断面表土中的强磁性矿物主要为磁铁矿和磁赤铁矿,并含有赤铁矿。阿拉善高原表土中磁性矿物颗粒多为多畴(MD),总体含量偏低,磁性矿物中硬磁组分含量较高;黄土高原区表土中磁性颗粒多为准单畴(PSD),总体含量偏高,磁性矿物中软磁组分含量较高。进一步分析发现,在干旱地区,频率磁化率与降水有良好的相关性,而常用的磁化率不能较好地反映降水量变化。本研究指示在干旱地区应用单一磁化率指标解释环境变化需要谨慎。
As one of the main environmental magnetic parameters, most vital proxies for climate reconstruction in loess study magnetic susceptibility has been used as one of the Progress has been made in using environmental magnetism to reconstruct climate change and environment records in Chinese loess studies, whereas there are still some issues not well understood. In this study, environmental magnetic investigations were conducted on surface soils along a NW-SE transect from the Chinese Loess Plateau to the Alxa Plateau. Sixty-two surface soil samples collected along the direction of the sharpest grads of the precipitation curve in the Loess Plateau and the Alxa Plateau area were analysed in the laboratory by using multiple environmental magnetic parameters （such as χlf, χfd%, χARM, SIRM, HIRM, SOFT, and back field IRM）, grain size, and the LOI. Results show that the magnetic assemblage in the surface soil is dominated by magnetite and maghaemite with some haematite. Hard magnetic content dominates the magnetic assemblage in eolian source area（e, g. the Alxa Plateau）whereas those in the dust depositing area（e, g. the Loess Plateau）were dominated by soft magnetic content. Cross plots of M,,/Ms vs. Bct/Bc and χfd% vs. χARM/SIRM indicate that the main magnetic grain sizes in surface soil are pseudo single domain（PSD） and muhidomain （MD）. The samples from the Alxa area are dominated by magnetic minerals with larger grain size while those from the Loess Plateau are dominated by fine magnetic minerals. The results indicate that the main magnetic minerals in the surface soil of the Loess Plateau were originated from both the eolian dust （autogeny） and pedogenic process （ secondary）, with the later dominated. Compared to magnetic susceptibility, frequency-dependent magnetic susceptibility shows a closer relationship with precipitation in a complex, large area with different basic substances and different physiognomy styles, which does not consistently agree with previous studies. This study indi
出处
《第四纪研究》
CAS
CSCD
北大核心
2007年第6期1001-1008,共8页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:40401064
40421101和90502008)
科技部重点国际合作项目(批准号:2002CB714004)
中国科学院寒区旱区环境与工程研究所创新项目(批准号:2003104)资助
关键词
环境磁学
降水量
表土
黄土高原
阿拉善高原
environmental magnetism, precipitation, surface soil, Loess Plateau, Alxa Plateau
