New Paleointensities From the Skinner Cove Formation, Newfoundland, Suggest a Changing State of the Geomagnetic Field at the Ediacaran-Cambrian Transition

Abstract

The geomagnetic field in the Ediacaran period appears to be characterized by anomalous directions, high reversal frequencies, and ultra-low field strength. At the Ediacaran-Cambrian transition, apparent polar wander paths become less controversial, but hyper-reversing fields with reversal frequencies similar to earlier in the Ediacaran have been reported until the mid-Cambrian. To understand the long-term behavior of the magnetic field during this transitional interval, information about the field strength is vital but currently lacking. To improve the intensity record at that time, samples of volcanic rocks from the 550 Ma Skinner Cove Formation, western Newfoundland, have been used for paleointensity determination. This multi-method paleointensity study, utilizing thermal and microwave Thellier as well as double-heating Shaw and pseudo-Thellier experiments produces paleointensity estimates of 2.6–10.3 μT, corresponding to virtual dipole moments of 0.65–2.25 × 1022 Am2. Analyses using scanning electron microscopy and rock magnetic measurements, as well as a positive intraformational conglomerate test, suggest that the remanence is primary. These intensity estimates are higher than earlier Ediacaran intensities and could point to the geomagnetic field entering into a stronger, more dipole-dominated state at the Ediacaran-Cambrian boundary.