STRANGE FIELD: PALAEOMAGNETIC BEHAVIOUR IN THE EDIACARAN

It has long been observed that palaeomagnetic poles derived from rocks of Ediacaran age do not lend themselves well to standard interpretation. This has led to this key period in Earth history becoming associated with somewhat controversial hypotheses such as extremely rapid plate motions, oscillatory true polar wander, and an equatorially dipolar palaeomagnetic field (i.e. poles offset by 90 degrees from those produced by the uniformitarian axial dipole). Only recently has the intensity of the palaeomagnetic field been measured alongside such pole positions. These provide very strong evidence that the magnitude of the field was very substantially weakened relative to recent times and most other intervals in Earth's history for which we have data.

The new and extant palaeomagnetic data present an emerging picture of a highly non-uniformitarian magnetic field lasting for at least the final 50 million years of the Ediacaran. Low field intensities probably accompanied a decrease in the relative size of the axial dipole component of the field and therefore the emergence of a more complex and time-varying global magnetic field morphology. This would have a significant impact on the reliability of palaeomagnetic records to provide a geographic reference frame for this time interval. These and other implications as well as potential causes of such palaeomagnetic field behaviour will be considered; they have a bearing on every level of our planet from the inner core to the exosphere.