Magnetic Lineations Observed Near the Ocean Floor and Possible Implications on the Geomagnetic Chronology of the Gilbert Epoch

Lineated magnetic anomalies, with a wavelength of 6 km and a peak-to-peak amplitude of 1500 nT,* were measured within 20 km of the continental crustal block of the tip of the Baja California peninsula of Mexico. The use of a high precision, local navigation system and measurements of the magnetic field close to the sea floor show that, at least in this small region, the sea-floor-spreading process has produced magnetic anomalies which are still lineated down to a scale of less than 1 km. These magnetic anomalies were formed during the younger part of the Gilbert Epoch of the geomagnetic time scale. Assuming that these anomalies were produced by uniform sea-floor spreading from a narrow zone of intrusion, the anomaly spacings can be used to establish revised estimates of the lengths of the magnetic reversals in this part of the Gilbert Epoch. They also indicate the absence of any previously undetected reversals of a duration of greater than 10 000 years.