ORIGIN OF MAGHAEMITE IN CHINESE LOESS DEPOSITS : AEOLIAN OR PEDOGENIC ?$

Maghaemite and magnetite, common ferrimagnetic minerals in surficial soils, have physical properties which are similar except for the thermal instability of the former. Utilising this exception, a study of thermomagnetic properties has been made to systematically separate these two magnetic components in loess and palaeosol samples from the upper parts of the Luochuan section of the central Chinese Loess Plateau. This investigation has shown that although maghaemite (thermally unstable component) occurs in greater amounts in palaeosols (MS=0.0187 Am2 kg−1±1.1%) than in loess units (MS=0.0156 Am2 kg−1±1.1%), in relative terms its contribution to the ferrimagnetic component of magnetisation is higher in the loess units (ΔMS (%)=32.2±2.0) than the soils (ΔMS (%)=23.5±3.7). Such an observation suggests that much of the maghaemite component originates in the aeolian source area, with some addition of pedogenic maghaemite occurring in the palaeosols.