陕西交道全新世黄土-黑垆土磁化率的CBD研究

MAGNETIC SUSCEPTIBILITY OF HOLOCENE LOESSBLACK LOAM SEQUENCE FROM JIAODAO, SHAANXI BEFORE AND AFTER CITRATE-BICARBONATE -DITHIONITE EXTRACTION

根据黄士高原中部交道剖面全新世黄土－黑垆土剖面的非磁滞磁化率和ＣＢＤ提取前后的磁化率、频率磁化率以及热磁分析结果，分析了磁性矿物的种类和磁畴状态，讨论了古土壤的磁化率增强，指出ＣＢＤ技术强有力的支持古土壤磁化率增强的土壤成因观点．虽然ＣＢＤ能非常有效地溶解土壤成因的磁赤铁矿，但并不是完全选择性地溶解土壤成因的磁铁矿颗粒．此外，通过对样品ＣＢＤ处理前后磁化率数据的分析，从土壤化学角度为黄土的风成说提供了新证据。

Magnetic susceptibility, anhysteretic susceptibility, frequency-dependent and temperature-dependent magnetic susceptibilities are measured before and after citrate-bicarbonate -dithionite (CBD) treatment on the Holocene loess-black loam sequence from Jiaodao, Shaanxi province. In this paper, we employ the correlativity between anhysteretic and magnetic susceptibilities to determine the domain state of magnetic minerals of the studied profile. The differences between pre- and post--CBD susceptibilities imply that not only the ultrafine superparamagnetic, but also some larger single-domain grains can be produced due to pedogenesis. Thermomagnetic analyses of the typical Holocene loess and black-loam specimens and magnetic susceptibility measurements before and after CBD treatment show that CBD has no absolute selectivity of dissolving the pedogenic magnetite grains, although it can efficiently dissolve the pedogenic maghemite grains. The results also show that CBD technique strongly supports the pedogenic model of susceptibility enhancement. In addition, a combination study of soil chemistry and rock magnetism supplies a new evidence for the eolian origin of Chinese loess.