Partly pedogenic origin of magnetic variations in Chinese loess
Partly pedogenic origin of magnetic variations in Chinese loess
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DOI：
10.1038/346737a0
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发表时间：
1990-08
期刊：
影响因子：
64.8
通讯作者：
L. Zhou;F. Oldfield;A. Wintle;S. Robinson;J. T. Wang
中科院分区：
文献类型：
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作者：
L. Zhou;F. Oldfield;A. Wintle;S. Robinson;J. T. Wang
层间风成粉砂（黄土）和埋藏土壤（古土壤）的第四纪序列可能提供过去气候的最佳陆地记录之一1 -5。中国黄土和古土壤序列中磁化率的变化与气候引起的深海沉积物中氧同位素比值的波动密切相关2 - 4，6 -8。作为对这种相关性的解释，有人提出，记录的磁化率变化主要取决于来自遥远但未知来源的均匀磁性组合的非磁性黄土组分的稀释程度6 -8。也有人认为，这样一个模型，涉及黄土的积累速度的变化叠加在一个恒定的磁通量的磁性粒子，提供了一个相对的地质时间尺度，通过控制黄土沉积天文调制的气候波动7。在这里，我们报告了这个模型的初步测试使用岩石的磁性特别敏感的磁性颗粒大小的变化。我们的研究结果表明，古土壤的特点是更精细的磁性粒度组合比介于黄土单位。这表明，一个简单的模型的基础上恒定的磁流入量和稀释量的非磁性黄土是不够的。我们的磁性测量结果建立了古土壤样品中的细粒磁性矿物与当代土壤中的细粒磁性矿物的密切可比性，从而指出古土壤中磁性矿物组合的部分成壤起源。
QUATERNARY sequences of interbedded aeolian silts (loess) and buried soils (palaeosols) potentially provide one of the best terrestrial records of past climates1–5. Magnetic susceptibility variations in loess and palaeosol sequences from China are strongly correlated with climate-induced fluctuations of oxygen isotope ratios in deep-sea sediments2–4,6–8. As an explanation of this correlation, it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non-magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6–8. It has also been suggested that such a model, involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles, provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7. Here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size. Our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units. This suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non-magnetic loess is inadequate. Our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols.