The investigation of magnetic properties at Site 1114 included (1) the measurement of bulk susceptibility of whole core sections, (2) point susceptibility and remanent magnetization of archive-half core sections, and (3) magnetic susceptibility and its anisotropy and remanent magnetization of discrete samples.
Magnetic susceptibility measurements were made on whole-core sections as part of the multisensor track (MST) analysis (see "Physical Properties"), and on half-core sections as part of the archive multisensor track (AMST) analysis. The MST and AMST susceptibilities values (uncorrected for volume) ranged between values on the order of 10-5 and 10-2 SI (Fig. F40).
The mean susceptibility, the degree of anisotropy (Pj) and the shape parameter (T) for the susceptibility ellipsoid (Jelinek, 1981), and the inclinations of the maximum (Kmax) and minimum (Kmin) susceptibility axes of the ellipsoid for discrete samples are shown in Figure F41. Mean susceptibilities were on the order of 10-3 to 10-2 SI; these values were notably higher than those at previous sites. The high susceptibility values suggest that ferrimagnetic minerals dominate the susceptibility. The Pj values averaged ~1.1 above ~120 mbsf. All samples except three showed T values above 0.5, indicating the predominance of oblate magnetic fabrics. Above 150 mbsf where data were corrected for tilted beds, Kmin axes were steep (ranging between ~60º and 90º) and Kmax axes were shallow (ranging between 0º and 25º). Data below ~150 mbsf were not interpreted because of the paucity of tilt-corrected data.
The oblate magnetic fabrics coupled with the subvertical orientations of Kmin axes and the subhorizontal orientations of Kmax axes probably reflect the compaction of sediments.
Measurements of remanent magnetization were made on relatively undisturbed sections from archive-half cores and on discrete samples taken from working-half core sections. Results are shown in Figures F42 and F43.
A total of 21 discrete samples were measured. Initial natural remanent magnetization (NRM) intensities were on the order of 10-2 to 10-1 A·m-1. About 30% or more of the initial intensity remained after AF demagnetization at 25 mT. Demagnetization behavior of discrete samples showed the presence of two or more magnetic components. A soft component was removed between 2 and 10 mT after the removal of a viscous component between 0 and 2 mT. The soft component generally showed a steep to moderately steep downward direction. After removal of the soft component, 9 of 21 samples showed a stable component that decayed approximately linearly toward the origin of the vector demagnetization plot between 15 and 25 mT (Fig. F42A, F42B); this component is referred to as the characteristic remanent magnetization (ChRM). The other samples yielded either curved demagnetization trajectories indicating significant overlap in the coercivity spectra of two components or linear trajectories not decaying toward the origin of the vector plot (Fig. F42C, F42D). The demagnetization behavior shown by these samples suggests the presence of another component with higher coercivities.
Intensity of remanent magnetization of long cores after AF demagnetization at 25 mT was dominantly on the order of 10-2 A·m-1. Low intensities on the order of 10-4 A·m-1 occurred near the top of the recovered section (Fig. F43.).
Inclinations showed dominantly normal polarities throughout most of the measured cores. Declinations were highly scattered as a result of the RCB drilling process. Discrete sample results did not consistently support the long-core data.
Because of poor recovery and discontinuous data sets, no attempt was made to interpret the data in terms of the magnetic polarity time scale.