Detailed paleomagnetic and rock magnetic studies have been conducted on eight deep-sea cores from the North Pacific. Magnetic studies include alternating field demagnetization, thermal demagnetization, anhysteretic remanent magnetization studies, magnetic hysteresis measurements over a variety of different temperatures, viscous and drying effects, strong field versus temperature measurements, x-ray diffraction, and x-ray fluorescence analyses. Six of the eight cores studied contain an abundance of fossils, particularly silicoflagellates, and appear to have acquired their remanent magnetization sufficiently close to the surface to reliably record the Earth's paleomagnetic field. The remaining two cores do not contain fossils and do not appear to accurately record the Earth's paleomagnetic field. Low-temperature oxidation appears to have occurred in situ in these cores. A gamma phase (cation-deficient spinel) iron-titanium oxide with lattice parameter of 8.38 A and Curie temperature of 545°C near the top of the cores changes with depth to a gamma phase with lattice parameter of 8.33 A and Curie temperature near 600°C close to the bottom of the cores. These chemical changes appear to be associated with the production of a chemical remanent magnetization that makes it impossible to use these cores for paleomagnetic studies. This work summarizes many of the problems in obtaining reliable paleomagnetic results from deep-sea cores, including possible spurious magnetic directions resulting from chemical changes, drying, and coring effects.
- Geological Society of America