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 540 cm long. Alternating-field (AF) demagnetization experiments using a stepwise AF field form 5 to 100 mT were conducted on all of the samples. The NRM intensities are 10-100 times higher than those commonly obtained from different localities. In the upper 460 cm of the core, most samples had stable single component magnetization, and remarkable high-stability components which survived up to 100 mT 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 30 mT, because the secondary magentizations 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 1 cc 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.