The last interglacial in the Chinese Loess Plateau: a petromagnetic investigation of samples from a north-south transect

Magnetic properties are reported for samples from the last-interglacial palaeosol, S1 ( = oxygen isotope stage 5), and its underlying loess, L2, at three sites representing the north (Wupu), middle (Yichuan) and south (Pucheng) portions of a 560 km transect across the Chinese Loess Plateau (CLP). The main objective was to test the magnetic model put forward by Evans and Heller (1994, Geophysical Journal International 117, 257-264) as a result of their work on the S3/L4 couplet, and to check to what extent it may vary in time and space. Their model argues for two magnetic components: an original aeolian input containing a mixture of hematite, magnetite and maghemite, superimposed upon which is a pedogenic component consisting of ultrafine magnetite particles. We find that the model is readily applicable, but that a difficulty arises at the southern end of the transect where it appears that wetter and warmer climatic conditions arrest, or even reverse, the magnetic enhancement typical of most soils across the CLP. A secondary aim was to assess the use of magnetic susceptibility to quantitatively estimate palaeo-precipitation. The methods of Maher et al. (1994, Earth and Planetary Science Letters 125, 461-471) and Han et al. (1996, Studia Geophysica et Geodaetica 40, 262-275) do not agree, and, once again, the southerly (wetter/warmer) gradient leads to particular difficulties. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.