Can relative paleointensities be determined from the normalized magnetization of the wind‐blown loess of China?

Abstract

Although the wind‐blown loess and interbedded paleosol sequence in the Loess Plateau of China has been extensively studied and regarded as one of the most complete terrestrial records of both the geomagnetic field and climatic changes during the Quaternary, little attention has been paid to it as a source of relative paleointensity. In this study, we examine the Malan loess (L1), the last glacial sediments, in the Lingtai section to determine whether loess is able to reliably record the relative paleointensity. Toward that end both the conventional normalizing method as well as the pseudo‐Thellier method [Tauxe et al., 1995] were used in conjunction with the examination of the rock magnetic properties and natural remanent magnetization (NRM). Rock magnetic properties of L1 show the uniformity in terms of magnetic mineralogy and grain size, suggesting that they may be suitable for relative paleointensity studies. Normalized remanences derived from L1 show highs between both 72–66 ka and 62–51 ka and lows near 63 ka, 42 ka and between 20 and 10 ka. Comparable results using different normalization parameters suggest that large‐amplitude variation of normalized magnetization may reflect the intensity variation of the geomagnetic field. However, comparisons of the normalized magnetization with contemporaneous marine records show some dissimilarities. In particular, the intensity low at 20–10 ka, corresponding to the last glacial maximum, is not compatible with the Sint‐800 composite record. On the other hand, spectral coherence analyses of middle‐ and high‐frequency components of the normalized magnetizations suggest some climatic influence. Thus this apparent discrepancy may be explained by climatic changes in the Loess Plateau and the resulting effect on the NRM.