ROCK-MAGNETIC PROXIES OF CLIMATE-CHANGE IN THE LOESS-PALEOSOL SEQUENCES OF THE WESTERN LOESS PLATEAU OF CHINA

Results of the first detailed study of the climate proxy record in the loess-palaeosol sequence at Xining-one of the few palaeoclimate sites in the currently arid western Loess Plateau of China-illustrate the i mportance of making many types of rock-magnetic measurements other tha n susceptibility. A multiparameter approach yielded confirmation that here, as elsewhere in the Loess Plateau, the susceptibility enhancemen t in palaeosols was caused primarily by ultrafine magnetite and maghae mite. Nevertheless, magnetic enhancement was caused not exclusively by changes in relative grain size, but also by variations in concentrati on and mineralogy of the magnetic fraction. The effects of concentrati on variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation r emanence, respectively. The resulting signal was ascribed more confide ntly to variation in magnetic grain size, which in turn was interprete d as a better proxy of pedogenesis than simple susceptibility. Variati ons in magnetic mineralogy were also determined to constrain interpret ations further. The data were then used to discuss climate history at Xining. Finally, results from Xining were compared with other western sites and contrasted with eastern sites. In summary: (1) data is prese nted from a new Loess Plateau site which also appears to yield a globa l climate signal; (2) a demonstration is made of a more rock-magnetica lly robust way to separate concentration, composition and grain-size c ontrols on susceptibility and other magnetic parameters; and (3) model s are provided for inter-regional comparisons of palaeoclimate proxy r ecords.