Magnetic characteristics of loess-paleosol sequences in Tacheng, northwestern China, and their paleoenvironmental implications

摘要

Systematic rock magnetic data including magnetic mineralogy and magnetic concentration (magnetic susceptibility, laboratory-induced magnetic remanences) are presented from the loess-paleosol sequences in Tacheng, northwestern China, to explore the specific paleoenvironmental significance of magnetic characteristics in the Xinjiang loess. Results show that ferrimagnetic minerals, such as magnetite and maghemite, dominate the magnetic properties in the Tacheng (TC) section, similar to the magnetic mineralogy of loess deposits in the Chinese Loess Plateau (CLP). The magnetic particles in the TC section are characterized by multi-domain (MD) and pseudo single domain (PSD) behavior, representing the detrital primary mineral phase. The absolute contents of pedogenic ultrafine superpara (SP) ferrimagnetic particles are very low in the TC section, indicating that pedogenesis has a limited contribution. This is quite different from the magnetic enhancement of loess deposits in the CLP. Variation of magnetic susceptibility and median grain sizes could be interpreted by the predominance of paleowind intensity as well as provenance variation. A similar pattern was also found in other places in Xinjiang, such as Talede section in Yili basin and Bole section in the western Tianshan. Our results suggest that variation of detrital inputs might have played a pivotal role in the enhancement of magnetic susceptibility while pedogenesis was probably responsible for the increase of finer single domain (SD) particles in paleosol units. The chi(ARM)/SIRM ratio could serve as an indicator for reflecting the degree of pedogenesis in Xinjiang loess. (C) 2014 Elsevier Ltd and INQUA. All rights reserved.