Evaluating the anomalous palaeomagnetic field behaviour in the Ediacaran with new palaeointensity data from Laurentia and Baltica.

Palaeomagnetic investigations from the Ediacaran period (635-541 Ma) give anomalous results, which might indicate unusual behaviour of Earth’s magnetic field. In contrast to the conventional geomagnetic dipole field, geocentric and aligned with Earth’s rotational axis, records of the palaeomagnetic field from several locations in Laurentia and Baltica indicate that the Ediacaran geomagnetic field might have been exceptionally weak and spent extended periods of time with its poles close to the geographic equator. Multi-method palaeointensity determinations have been performed on rocks from the Grenville Dykes (Canada, 584-598 Ma), Skinner Cove volcanics (Newfoundland, 550.5 Ma) and the Volyn Traps (Ukraine, 560-580Ma), confirming that the field was exceptionally weak, with VDM values between 4 and 15 ZAm². These values could correspond to considerably lower VDM strengths predicted by geodynamo simulations for fields with low dipolarity before the onset of nucleation of the solid inner core. In contrast, preliminary evaluation of published directional data indicates that palaeosecular variation in the Ediacaran might not be distinguishable from palaeosecular variation predicted from palaeomagnetic data of the last ten million years.

These new palaeointensity results contribute to the elimination of data gaps in the Neoproterozoic palaeomagnetic record and will be used in combination with qualitatively assessed published directional and intensity data to capture the behaviour of the geomagnetic field of this time period in statistical field models. Comparisons of time averaged palaeosecular variation and VDM distribution with predictions of the geomagnetic field from geodynamo simulations will help to verify and improve models of deep Earth structures and dynamics.