The investigation of magnetic susceptibility variation mechanism of Tien Mountains modern loess: Pedogenic or wind intensity model?

Abstract

It had been widely accepted that in situ pedogenic enhancement of fine grained ferromagnetic content provides the well-established patterns of magnetic susceptibility variation within mid-latitude loess deposition, such as those of Chinese Loess Plateau and Central Europe. An entirely different phenomenon is present in higher latitude loess deposition of Alaska and Siberia, with high magnetic susceptibility in loess and low in soil. This inverse relationship has suggested that magnetite grain size is related to wind velocity. The Tien Mountains are located at the transition zone between the Chinese Loess Plateau and Siberia, and have extensive loess deposits. Previous investigations have displayed a more complex correlation between pedogenesis and magnetic susceptibility with positive and negative relationships coexisting. Further research has indicated that a reducing environment must be an important influence in decreasing magnetic susceptibility of basal soil units in this area. Tien Mountains loess has similar magnetic mineralogy to Chinese Loess Plateau loess, and pedogenic magnetite effectively influences magnetic properties. However, magnetic susceptibility does not perfectly correspond to weathering intensity change, the result of high concentration and unstable primary magnetite among loess samples. Pedogenic magnetic material controls magnetic susceptibility variation gradually as pedogenic intensity increases. Magnetic susceptibility is not a great proxy of loessic soil unit pedogenic intensity in this region, especially for weakly pedogenic soil units.