Bijaksana, Satria (1996): Magnetic anisotropy and correction of paleomagnetic inclination shallowing in deep-sea sediments. 180 pp., georefid:1998-059328
Abstract:
The inclination (I (sub obs) ) of natural remanent magnetization (NRM) in sediment may be shallower than the inclination (I (sub H) ) of the Earth's field in which it is acquired. This thesis investigates whether such inclination shallowing can be detected and corrected for by measuring the magnetic anisotropy of the sediment. Paleomagnetism and magnetic anisotropy were measured for 79 turbidite specimens from 3 cores on the Scotian Rise, 87 pelagic clay specimens from DSDP site 578, and 90 pelagic lime-mud specimens from DSDP site 606. For the turbidites, I (sub obs) is on average 12 degrees shallower than the 61 degrees expected from the geocentric axial dipole (GAD) model. The turbidites are also highly anisotropic with the ratio of anhysteretic remanence (ARM) along the hard axis (ARM (sub min) ) to that along the easy axis (ARM (sub max) ) averaging 0.82. A significant correlation between tan I (sub obs) and ARM (sub min) /ARM (sub max) exists as Hodych and Bijaksana [1993] showed was expected from the theory of Jackson et al. [1991]. The correlation line's estimate of tan I (sub obs) when ARM (sub min) /ARM (sub max) = 1 predicts I (sub H) = 69 degrees (+5 degrees /-10 degrees ) with 95% confidence agreeing with the expected 61 degrees . The turbidites show a significant correlation between tan I (sub obs) and the degree of compaction Delta V. The correlation line's estimate of tan I (sub obs) when Delta V = 0 predicts I (sub H) = 71 degrees (+6 degrees /-12 degrees ) agreeing with the 61 degrees and suggesting that the inclination shallowing is compaction-induced. A significant correlation between ARM (sub min) /ARM (sub max) and Delta V suggests the ARM anisotropy is also compaction-induced. Compaction experiments on a few specimens further support a compaction origin for the ARM anisotropy and the inclination shallowing. For the turbidites, the susceptibility anisotropy was similar to but smaller than the ARM anisotropy. The ratio of susceptibility along the hard axis (chi (sub min) ) to susceptibility along the easy axis (chi (sub min) ) averaged 0.90. A significant correlation was found between chi (sub min) /chi (sub max) and ARM (sub min) /ARM (sub max) and hence between tan I (sub obs) and chi (sub min) /chi (sub max) . The latter correlation line's estimate of tan I (sub obs) when chi (sub min) /chi (sub max) = 1 predicts I (sub H) = 67 degrees (+6 degrees /-13 degrees ). This prediction is as successful as that using ARM (sub min) /ARM (sub max) and is much faster to measure. An attempt was made to study the pelagic clays and pelagic lime-muds in a similar fashion. However, inclination shallowing only averaged 1 degrees for the pelagic clays and 4 degrees for the pelagic lime-muds and ARM anisotropy was also very low. The low inclination shallowing and anisotropy in these pelagic sediments are probably due to relatively low compaction.
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West: -80.0000 East: 151.3745 North: 75.0000 South: -57.0000
West: NaN East: NaN North: NaN South: NaN
West: NaN East: NaN North: NaN South: NaN
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