Experimental Study On Re-deposition Of Loess Sediments Under Different Magnetic Field Intensities

The aeolian loess-paleosol sediments on the Chinese Loess Plateau provide reliable paleoclimatic and magnetostratigraphic records for the last 2.6 Ma.Because Chinese loess-paleosol sediments include magnetic minerals of aeolian and pedogenic origins,as well as different characteristic remanent magnetization?ChRM?directions of the same geomagnetic reversal were observed from different loess sections or from multiple sets of parallel samples of the same loess section,a hot debate on the reliability of paleomagnetic records in Chinese loess-paleosol sediments,especially those deposited in weak magnetic fields,still remain.In order to clarify whether the magnetic particles of loess-paleosol sediments can accurately record the peripheral magnetic field in the weak magnetic field,re-deposition experiments in different magnetic fields have been carried out for loess-paleosol sediments from the Baoji section.Based on the anisotropy of magnetic susceptibility?AMS?and paleomagnetic results of re-deposition experiment samples,several main achievements are summarized as follows:1.The AMS results show that all the re-deposition samples obtained under different magnetic fields have horizontal K_maxax and K_intnt directions and vertical K_minin directions,which is fully consistent with the primary sedimentary fabric of original deposits and with natural loess-paleosol sediments.2.No matter re-deposition experiment samples obtained in the magnetic field intensity similar to the present geomagnetic field or a clearly weaker magnetic field,their ChRM directions reveal the same polarity as the imparted magnetic field.That is to say,when re-deposition experiment samples obtained under the normal magnetic field,their ChRM directions show a normal polarity,and when they obtained under the reverse magnetic field,their ChRM directions reveal a reverse polarity.3.The results of the re-deposition experiments support that the Chinese loess-paleosol sediments can effectively record the signals of geomagnetic changes even in the weak magnetic field equal to one tenth of the present geomagnetic field intensity.