MAGNETIC PROPERTIES OF LOESS DEPOSITS ON THE NORTHEASTERN QINGHAI-TIBETAN PLATEAU: PALAEOCLIMATIC IMPLICATIONS FOR THE LATE PLEISTOCENE

Abstract

The loess-palaeosol deposit on the northeastern Qinghai-Tibetan Plateau is sensitive to environmental changes, thus providing a good opportunity to investigate regional palaeoenvironmental evolution and its relationship with global climatic changes. Detailed rock magnetic investigations and grain-size determination were carried out on a 35-m-thick loess-palaeosol sequence at Dongchuan, the northeastern Qinghai-Tibetan Plateau. The principal ferrimagnetic minerals in both the loess and palaeosol units are large pseudo-single domain magnetite/ maghemite. Palaeosol units are generally enriched in ultrafine-grained magnetite/maghemite of pedogenic origin. Variations of low-field magnetic susceptibility and frequency-dependent susceptibility in the loess and palaeosols can mainly be attributed to changes in the concentration of these minerals. Higher values of frequency-dependent susceptibility occur in the palaeosol horizons except for the weakly developed palaeosol, suggesting that higher concentrations of ultrafine magnetite/maghemite particles occur in palaeosol units due to in situ pedogenesis. The frequency-dependent susceptibility of the loess units is very low and uniform, indicating absence of the super-paramagnetic grains and negligible pedogenically induced enhancement of magnetic susceptibility. Generally, magnetic susceptibility combined with the frequency-dependent susceptibility of the loess-palaeosol sequences reflect the glacial-interglacial changes, thus can be employed as a proxy measure of palaeoclimate in this region. However, the low-field magnetic susceptibility record does not consistently correlate to the variations in stratigraphy of the Dongchuan loess-palaeosol sequence. It is thus suggested that multiparameter rock magnetic investigations combined with non-magnetic measurements, such as grain-size analysis, represent a more powerful approach for palaeoclimatic research into the complex loess-palaeosol record in the Qinghai-Tibetan Plateau. © 2006 The Authors Journal compilation © 2006 RAS.