Characteristics of the natural remanent magnetization (NRM) of a core collected from offshore Wilkes Land, East Antarctica

Abstract

Paleomagnetic and rockmagnetic studies were carried out in order to investigate the characteristics of natural remanent magnetization (NRM) of deep-sea sediments cored from offshore Wilkes Land, East Antarctica. The core is 540cm long. Alternating-field (AF) demagnetization experiments using a stepwise AF field from5to100mTwereconductedonallofthesamples. TheNRMintensitiesare10-100 times higher than those commonly obtained from different localities. In the upper 460cm of the core, most samples had stable single component magnetization, and remarkable high-stability components which survived up to 100mT were observed. In the lower section of the core, in contrast, many samples showed more unstable (zigzag) demagnetization curves and secondary acquired magnetizations. The optimum AF demagnetization field intensity was assumed to be 30mT, because the secondary magnetizations of every sample seemed to be completely demagnetized at that AF field. The down core NRM variation after demagnetization by the optimum field revealed that the core contains 3 polarity intervals. By using smaller cubic samples of 1cc volume, the time resolution of the paleomagnetic record was much improved. Anhysteretic remanent magnetization (ARM) experiments were also conducted on all of the samples. The results of the AF demagnetization of ARM imply that the samples showing only soft NRM component possibly acquired their magnetization under a weak geomagnetic field.