Remagnetization mechanism and a new age model for L9 in Chinese loess

Chinese loess during the Quaternary is important for both paleomagnetic and paleoclimatic studies. Although magnetostratigraphy has been used for the initial loess timescale, paleomagnetic records in loess still remain in debates, such as magnetic polarity anomalies in L9, which is a thick and coarse sandy horizon as a typical marker bed. To better understand the magnetization mechanism of these anomalies, a new age model for L9 was first constructed based on a new correlation between loess and marine δ18O, which proposed that L9 should be correlated to marine oxygen stage (MIS) 20–24, not 22–24 as previous suggested. Using combined grain size and environmental magnetism parameters, an extended climatic optimum corresponding to MIS 21 can be identified in middle of L9. A remagnetization mechanism of viscous remanent magnetization overprinting on characteristic remanent magnetization (ChRM) carriers (mainly large pseudo single domain and multidomain magnetite particles), associated with the chaotic detrital remanent magnetization caused by low efficiency alignment of ChRM carriers along with the ambient field during deposition, is proposed to interpret the magnetic anomalies. This study provides new insights into the magnetization mechanism of the Chinese loess, and the new age model for L9 helps to accurately refine the finer scale correlation of paleoclimatic records between the Chinese loess and marine sediments.