Multiple origins and interpretations of the magnetic susceptibility signalin Chinese wind-blown sediments

In most Chinese loess-paleosol sequences, high magnetic susceptibility valu es are found in the soil horizons, with low values in the loess layers. The susceptibility signal has been widely used as a proxy climatic indicator. However, both the causes and mechanisms which control susceptibility still remain controversial. Our recent studies challenge some earlier interpretat ions of the magnetic susceptibility signal in Chinese wind-blown sediments. First, the prevailing hypothesis of pedogenic origin cannot totally accoun t for the susceptibility variations in many sections. Second, in some cases , the principal carrier of the magnetization seems not to be the ultrafine pedogenic minerals, rather coarse lithogenic magnetic minerals derived from local sources can also contribute significantly to the susceptibility sign al. Finally, not all the Chinese soils have higher susceptibility values th an that of loess or sand layers, opposite relationships do exist. It is con cluded that the source and causes of susceptibility may be different from s ite to site or even at different times at a given site. Any single hypothes is cannot completely account for the susceptibility variations in the Chine se Loess Plateau and its surrounding regions. Besides the previous explanat ions of carbonate leaching, pedogenic processes and organic decomposition, the contribution of source materials to magnetic susceptibility must also b e taken into account. (C) 2000 Elsevier Science B.V. All rights reserved.