Paleoclimatic significance of mineral magnetic properties of loess sediments in northeastern Qinghai-Tibetan Plateau

Loess deposit in the northeastern Qinghai-Tibetan Plateau offers an excellent record of climate and environment changes in this region. We have conducted multiparameter mineral magnetic analyses of samples of loess deposits from the Dongchuan, Lalakou and Panzishan sections.The methods used include magnetic susceptibility, frequency-dependent susceptibility, temperature-dependent susceptibility, isothermal remanent magnetization acquisition,and magnetic hysteresis loops. The results reveal that magnetite is the dominant contributor to magnetic susceptibility.Maghemite and hematite is also present in the loess layersand paleosol horizons. The higher concentration ofmaghemite in paleosols suggests that the formation ofmaghemite occurred during in situ pedogenesis, which playsan important role in the enhancement of the magnetic susceptibility.Similar to that in the Chinese Loess Plateau lyingto the east of the Liupan Mountains, magnetic granulometryin the studied loess and paleosols is predominantly pseudosingle-domain (PSD). However, the mean grain-size of theferrimagnetic minerals in loess is evidently coarser (largerPSD and multidomain-like) than in paleosols (mainly PSD).The magnetic susceptibility of loess and paleosols is positivelycorrelated with the content of ultrafine magnetite/maghemitegrains, and hence with the intensity of in situ pedogenesis.Therefore, the enhanced magnetic susceptibility in the studiedloess-paleosol sequences can be interpreted as being dueto climatically induced in situ pedogenesis