Anomalous high coercivity natural remanent magnetization acquired by maghemite in Deep-sea Sediments off Wilkes Land, East Antarctica

• Main Authors: 松岡 東香, マツオカ ハルカ, Haruka MATSUOKA
• Format: Thesis
• Language: English
• Published: 2004
• Subjects: Antarctic; East Antarctica; The Antarctic; Wilkes Land; Antarc*; Antarctica
• Online Access: https://ir.soken.ac.jp/?action=repository_uri&item_id=826; http://id.nii.ac.jp/1013/00000826/

The magnetic properties and minerals of a deep-sea sediment core obtained from off Wilkes Land have been investigated in order to obtain paleomagnetic, rock-magnetic and paleoenvironmental data for Antarctic region. The core used in this study was collected from a continental rise site 3060m deep at the western part of the Antarctic Wilkes Land margin during the TH94 cruise (1994-1995) of R/V HAKUREI-MARU, carried out by the Technology Research Center, Japan National Oil Corporation. The core consists of siliceous silt and is characterized by its brownish gray color, an absence of paleoclimatically induced lithological variations and abundant foraminiferal contents in good preservation. Paleomagnetic measurements reveal that the sediment core has an anomalous natural remanent magnetization (NRM). The original NRM intensities of sediments are 10-100 times greater than those commonly observed at different localities. The high median destructive field value of about 60mT in overall average suggests a remarkable high stability of NRM. The high coercive components of NRM have never been demagnetized completely and the more than 20% of the primary NRM can survive even after the AF demagnetization with peak fields of 100mT. The NRM intensity decay curves of most samples at AF demagnetization depict unusual straight line, indicating that each sample has an anomalous flat distribution in the coercivity of NRM carrier grains. Magnetostratigraphy proves that the core covers the last 1 Ma. The employment of 1 cc small-volume samples for paleomagnetic measurements proves its advantage of deriving the higher time resolution records from sediments by comparison with the paleomagnetic data obtained by using common U-channel and 7cc samples. The employed 1 cc samples provide a long-term secular variation in declination, which correlates with those of well-dated cores in previously published study. That correlation enables an age control for the core, and the sedimentation rate are estimated to be 2-9 mm kyr -1 with the ...