Duration dependence of magnetic susceptibility enhancement in the Chinese loess–palaeosols of the past 620 ky

摘要

Past climate has been interpreted from the loess–palaeosol record found in China. There is no argument that the palaeosols are more strongly weathered than the underlying less well-weathered loess and that these changes have been governed by glacial/interglacial climate fluctuations. However, the duration of pedogenesis may have also contributed to the development of palaeosol properties. Previous studies have not attempted to separate these two factors which both affect the intensity of soil formation, and have assumed that the degree of soil development and pedogenic magnetic susceptibility enhancement depended solely on the climate conditions. We show that the magnetic susceptibility enhancement of palaeosols of the lower Malan and upper Lishi Formations (S_1–S_5 correlated to the interglacials of the past 620 ky) depends partly on the duration of pedogenesis. This suggests that pedogenic magnetic susceptibility enhancement of palaeosols should not be used for such direct palaeoclimate reconstructions as determining the amount of rainfall or the temperature of the soil-forming intervals. However, used in combination with other proxies (other magnetic properties, % Fed, Fed/Fet, color indices, the depth of decalcification, particle size), magnetic properties of palaeosols and loess layers can provide valuable insight into climatic conditions of soil-forming episodes. It follows that multiproxy evidence provides better insight into climate dynamics than the interpretation of a single proxy.