PEDOGENIC FACTORS AFFECTING MAGNETIC SUSCEPTIBILITY OF THE LAST INTERGLACIAL PALAEOSOL S1 IN THE CHINESE LOESS PLATEAU

Authors

Z.-D. Feng, Montclair State University
H. B. Wang, National Laboratory of Western China’s Environmental Systems, MOE, Lanzhou University, Lanzhou, Gansu 730000 China
C. G. Olson, USDA, NRCS, National Soil Survey Center, 100 Centennial Mall North, Lincoln, Nebraska

Date of this Version

September 2004

Comments

Published in Earth Surf. Process. Landforms 29, 1389–1402 (2004).

Abstract

The magnetic susceptibility has been used as a quantitative or semi-quantitative proxy for reconstructing the summer monsoon intensity in the Chinese Loess Plateau based on extensive studies on climatic or/and environmental mechanisms producing the magnetic susceptibility signatures. However, the precise nature of the link between past climates and the susceptibility signatures has remained uncertain primarily due to lack of our understanding in the finalizing and preserving processes of the signatures. This paper attempts to examine the reliability or acceptability of this summer monsoon proxy from non-magnetic perspectives of soil-forming processes. We chose nine sections along two transects: one across the western part of the Chinese Loess Plateau and another across the eastern part. Several conclusions can be drawn from our analytical data. First, clay translocation within the S1 palaeosol profiles, as indicated by field-observed clay coatings on ped faces in Bt and Bk horizons and demonstrated by laboratory-analysed clay contents, must have moved some of the magnetic minerals downward so that the susceptibility reflects only the post-translocation distribution of the magnetic-susceptibilityproducing minerals. Second, the best-developed palaeosol S1S3 at most of the sections studied is not expressed by the magnetic susceptibility because this palaeosol developed in underlying coarse loess (L2) and coarse textures tend to lower the susceptibility. Third, carbonate concentration is normally negatively correlated with the magnetic susceptibility or simply suppresses the magnetic susceptibility peak when the susceptibility enhancement exceeds the carbonate dilution effect. To conclude, extreme caution must be observed when using magnetic susceptibility signatures to retrieve high-resolution records of the last interglacial palaeoclimate in the Chinese Loess Plateau.