Gauss-Matuyama极性转换期间地球磁场方向和强度变化特征

粒度分析和风化强度研究表明 ,黄土高原渭南阳郭剖面黄土层L33沉积期间成壤化作用相对较弱 .在此基础上 ,为研究极性转换期间地球磁场变化特征 ,本文对黄土层L33进行了详细的岩石磁学和古地磁学研究 ,其结果表明黄土层L33的主要载磁矿物为磁铁矿和磁赤铁矿 ,并以沉积剩磁为主 ;由逐步热退磁确定的特征剩磁 （ChRM ）揭示了G M（Gauss Matuyama）极性转换过程的持续时间为 9 43± 0 64ka;在G M极性转换之前 ,地球磁场曾发生过持续时间为 2 2± 0 1 3ka的短极性漂移事件 ;相对强度研究表明 ,G M极性转换期间地球磁场强度减弱 .

GAUSS-MATUYAMA POLARITY TRANSITION OBTAINED FROM A LOESS SECTION AT WEINAN,NORTH-CENTRAL CHINA

A record of Gauss Matuyama （G/M） geomagnetic polarity transition has been obtained from a loess section at Weinan, Shaanxi Province in China. Grain size and weathering intensity analysis demonstrate a rather weak pedogenesis in the oldest loess unit L33 was deposited. Rock and paleo magnetic investigations indicate that the remanent magnetization is mainly carried by magnetite and maghemite deposited as detrital grains. The record of the polarity transition based on ChRM directions of the low coercivity magnetic phase comprises 33 transitional directions. A pre transitional excursion defined by 4 intermediate directions and lasting about 2.2±0.13 ka appears to have occurred prior to the G/M polarity transition. Then, the record displays a N-S-N cycle with VGPs locating principally on American and Eastern Asia longitudes. Finally, the reverse polarity is established with VGPs clustering in the Atlantic near southern Africa. The total duration of the directional change for the G/M transitions at Weinan, as derived from independent loess accumulation ratios, is about 9.43±0.64. During the G M polarity transition, the decrease in field intensity occurs.