PALEOCLIMATE IMPLICATIONS OF MAGNETIC PROPERTIES AND MINERALOGY OF THE CHINESE LOESS/PALEOSOL COUPLETS OF THE LAST 1.2 MA

A multiparameter investigation of 15 loess-paleosol couplets (S0/L1 to S14/L15) from the Jiaodao section sequence in the central loess plateau of China using mineral magnetic approaches was conducted. The magnetic parameters display systematic variations that seem to be closely related to paleoclimate variations and intensity of pedogenesis. High-temperature and high-field magnetic properties exhibit systematic variations that can be directly related to magnetic mineral transformations by pedogenic processes. High-temperature susceptibility curves of paleosols show a generally decreasing trend in reversibility from the base of the Lishi Formation to the Holocene black loam, indicating a decrease in weathering intensity. This may reflect a long-term increase in aridity and/or a general long-term cooling trend of the interior of the Asian continent from 1.2 Ma ago to the present. Some samples display wasp-waisted hysteresis loops. These are most pronounced in moderately enhanced paleosols, less pronounced in the practically unaltered loess, and subdued in the well-developed paleosols, but wasp-waistedness reappears in the most developed paleosols. These magnetic variations in Chinese loess and paleosols are jointly controlled by the changes in composition, concentration and grain-size, but each variable has different effects at different stages of pedogenesis.