Résumé
Oligocene basal sediment samples from Hole U1439A, located on the Izu-Bonin-Mariana fore arc, were measured to determine paleomagnetic polarity and paleoinclination. A total of 57 samples from Cores 352-U1439A-16X through 19X were measured using thermal demagnetization to isolate the characteristic remanent magnetization (ChRM). The samples were relatively strongly magnetized, with about half having natural remanent magnetization intensities >100 mA/m. Most samples produced demagnetization results consistent enough to calculate a ChRM direction using principal component analysis, but the intrasample demagnetization consistency ranged from good to poor, indicating variable sample recording fidelity. Paleoinclination values indicate at least two polarity zones, with a zone of normal polarity in Cores 16X and 17X overlying a reversed polarity zone in Core 18X. Unfortunately, normal paleoinclination values are significantly higher than reversed values, indicating that a downward-pointing overprint, probably caused by the drill string, was not completely removed by the demagnetization procedure. Thus, the paleoinclination values appear biased.