Pedogenesis and paleoclimate: interpretation of the magnetic susceptibility record of Chinese loess-paleosol sequences

In the Chinese loess-paleosol sequences from Luochuan, Haanxi province, China, variations in the magnetic susceptibility have been accepted as an excellent proxy for paleoclimate, and the standard interpretation is that climatic processes have enhanced the magnetic susceptibility of the paleosols beyond the base-line level of the loess. By using mineral magnetic properties and a soil-chemistry extraction procedure, we show that most of the magnetic susceptibility signal in both the paleosols and the loess is due to pedogenesis. In effect, loess deposition and pedogenesis are competing processes at all times, and the presence of a paleosol simply indicates that the latter process was predominant. These results imply that any interpretation of the paleoclimate record of loess-paleosol sequences must recognize the pedogenic nature of the magnetic susceptibility signal and that the focus of future research must be on the critical role of climate in the development of the paleosols.