1 Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 
2 China University of Geosciences, Beijing 100083, China; 
3 School of Information Science and Technology, Beijing Institute of Technology, Beijing 100081, China

Detailed magnetostratigraphic and rock magnetic investigations on L8?S12 of the Songjiadian loess section in the Sanmenxia area, southernmost margin of the Chinese Loess Plateau were conducted in this study. Matuyama/Brunhes (M/B) boundary occurred at the bottom of the loess unit L8. The top and bottom boundaries of the Jaramillo polarity subchron are found in the middle of L10 and the bottom of L12, respectively. Magnetic fabric of the loess layers maintains the original depositional features and the recorded remanent magnetization analysis indicates little post-deposition disturbance experienced. In late Matuyama chron, two anomalies of geomagnetic field have been detected in L9. Our data demonstrated that these recorded anomalies were less likely a result of remagnetization, but more possibly the signature of geomagnetic excursions occurred, named SJD1 and SJD2. It is calculated that the midpoint ages of SJD1 and SJD2 are 0.917 Ma and 0.875 Ma, respectively, and the time-interval between the two events approximates 12 ka. Chronologically, SJD1 is close to the Santa Rosa (0.922 Ma) and SJD2 corresponds to the Kamikatsura (0.886 Ma) excursions. In consistence with previous studies, the geomagnetic field was weakened during these events.

This work was supported by the National Natural Science Foundation of China (Grant Nos. 40672114 and 40872112).