Long-Term Magnetic Field Change And Environmental Magnetic Study In The Northwestern Sub-Sea Basin Of The South China Sea

Marine sediments could record relatively continuous information on paleomagnetic and paleoceanographic changes.By normalizing the natural remanent magnetization(NRM)recorded by marine sediments by magnetic concentration-related parameters,it is possible to reconstruct the relative paleointensity(RPI)record of the geomagnetic field,which is of great significance for studying the evolution of the geomagnetic field and the comparison of global RPI records.At present,because of the lack of high-precision RPI records in the South China Sea,especially in the Northwest Sub-basin,understanding of fine features of the geomagnetic field evolution in this region has been hindered.To this end,this project systematically investigated the gravity core L07 collected form the northwestern basin of the South China Sea using both rock magnetism and paleomagnetism.The isothermal remanent magnetization(IRM)was used as the normalized parameter of NRM to reconstruct the RPI curve since the 37 ka BC in the northwestern basin of the South China Sea.Our results show that the magnetic bearing minerals in the L07 core sediments are relatively uniform and are mainly pseudo-single domain(PSD)low-coercivity magnetites.The paleomagnetic inclination data shows that the inclination is negative at 220 cm and is accompanied by the low value of RPI,which is consistent with the data of the Core PC83 in the northwestern basin of the South China Sea.We believe that the lowest RPI and negative inclination values at 200 cm correspond to the geomagnetic excursion event: “Mono Lake” polarity event.In addition,we also found that a RPI peak is shown at 10.5 ka By combining the RPI records from the Okhotsk sea in East Asia,we contribute this RPI peak to effects of the non-dipole field.More specifically,the magnetic flux anomaly at high latitudes could have significant impacts on paleomagnetic information at the mid-low latitudes.