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/Br...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.展开更多
405 samples were collected from L5-S5-L6 in consideration of obvious variations in susceptibility of the geological sections, which are section Xifeng in Gansu Province and section Duanjiapo in Shaanxi Province for st...405 samples were collected from L5-S5-L6 in consideration of obvious variations in susceptibility of the geological sections, which are section Xifeng in Gansu Province and section Duanjiapo in Shaanxi Province for study of magnetotactic bacteria (MB) and magnetosomes (MS) in Chinese loess-paleosol sequences. MB in each sample were observed by TEM after being cultured under 8-18℃, room temperature (RT), 25℃, 26℃ and 30℃ conditions. In general, MB are distributed widely in loess-paleosol sequences, fewer in loess layers with predomination of vibriod in shape. However, there are more MB in paleosol layers with morphological varieties such as roddish, vibriod and occasionally approximately coccus. The magnetosomes (MS) in MB of paleosol are usually arranged in chains along the cells. It was also found that MB growth and MS formation are associated with the environment in which MB live. It can be inferred from the distributions of MB and MS that the paleoclimates fluctuated during the formation of展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos.40672114 and 40872112)
文摘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.
文摘405 samples were collected from L5-S5-L6 in consideration of obvious variations in susceptibility of the geological sections, which are section Xifeng in Gansu Province and section Duanjiapo in Shaanxi Province for study of magnetotactic bacteria (MB) and magnetosomes (MS) in Chinese loess-paleosol sequences. MB in each sample were observed by TEM after being cultured under 8-18℃, room temperature (RT), 25℃, 26℃ and 30℃ conditions. In general, MB are distributed widely in loess-paleosol sequences, fewer in loess layers with predomination of vibriod in shape. However, there are more MB in paleosol layers with morphological varieties such as roddish, vibriod and occasionally approximately coccus. The magnetosomes (MS) in MB of paleosol are usually arranged in chains along the cells. It was also found that MB growth and MS formation are associated with the environment in which MB live. It can be inferred from the distributions of MB and MS that the paleoclimates fluctuated during the formation of
