Gauss-Matuyama Polarity Transition Obtained from a Loess Section at Weinan, North-Central China
Gauss-Matuyama Polarity Transition Obtained from a Loess Section at Weinan, North-Central China
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DOI：
10.1002/cjg2.81
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发表时间：
2000-09
期刊：
影响因子：
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通讯作者：
R. Zhu;B. Guo;Z. Ding;Zhengtang Guo;A. Kazansky;G. Matasova
中科院分区：
文献类型：
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作者：
R. Zhu;B. Guo;Z. Ding;Zhengtang Guo;A. Kazansky;G. Matasova
在陕西渭南的中国黄土剖面上，获得了Gauss-Matuyama(G/M)地磁极性转变的记录。粒度和风化强度分析表明，在最古老的黄土单元L33沉积时，发生了较弱的成壤作用。岩石磁学和古磁学研究表明，剩余磁化作用主要由以碎屑颗粒形式沉积的磁铁矿和磁铁矿携带。根据低矫顽力磁相的特征剩磁(ChRM)方向记录的极性转变包括33个转变方向。由4个中间方向定义的过渡期前漂移，持续约2.2±0.13ka，似乎发生在G/M极性转变之前。然后，记录显示了一个N-S-N旋回，虚地磁极主要位于美国和东亚经度上。最后，随着VGP聚集在靠近南部非洲的大西洋，以一种让人想起最近在Searles山谷重新研究的G/M转变的记录的方式，建立了相反的极性。然而，渭南和塞尔斯谷的记录仍然存在显著差异。因此，这一转变过程中的场形可能比由赤道偶极子或低阶纬向非偶极子分量主导的场形更为复杂。由独立的黄土堆积速率推算的渭南G/M转变的总持续时间约为9.43±0.64 ka。
A record of Gauss-Matuyama (G/M) geomagnetic polarity transition has been obtained from the loess section at Weinan, Shaanxi Province in China. Grain size and weathering intensity analyses demonstrate that a rather weak pedogenesis occurred when the oldest loess unit L33 was deposited. Rock-magnetic 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 characteristic remanent magnetization (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 virtual geomagnetic poles (VGPs) locating principally on American and Eastern-Asia longitudes. Finally, the reverse polarity is established with VGPs clusting in the Atlantic near southern Africa, in a manner reminiscent of the record of the G/M transition recently restudied at Searles Valley. However, significant differences still exist between the Weinan and Searles Valley records. Thus, the field configuration during this transition might be more complicated than one dominated by an equatorial dipole or low-order zonal non-dipole components. The total duration of the directional change for the G/M transition at Weinan, as derived from independent loess accumulation rates, is about 9.43 ± 0.64 ka.