Behaviour of the Earth's Palaeomagnetic Field from Small Scale Marine Magnetic Anomalies

Abstract

CERTAIN areas of the ocean crust exhibit a high resolution recording of the magnetic field history. A recent survey¹ of the Gorda-Juan de Fuca Rise area in the North Pacific displays short wavelength (10 to 20 km), low amplitude (40 to 80 gamma) features superimposed upon the larger scale (30 to 200 km, 200 to 800 gamma) magnetic anomaly pattern of Heirtzler et al.². Many of these small scale anomalies form lineations which are parallel to the major magnetic lineations of Heirtzler et al. Sequences of small scale anomalies form characteristic patterns within intervals previously thought to be of constant polarity. We have identified two of these patterns that we observed in the North Pacific on profiles from the South Pacific and South-east Indian Oceans. Because of their global distribution, we conclude that the small scale anomalies are due to time variations of the Earth's magnetic field. That is, these features record either short (less than 3 × 10⁴ yr) polarity reversals or fluctuations in the intensity of the dipole moment, perhaps with periods greater than 3 × 10⁴