Long-term variations in geomagnetic field behaviour contain essential information on deep Earth processes through geological time. Palaeomagnetic investigations from the Ediacaran period (635-541 Ma) are known to give anomalous results, showing ambiguous apparent polar wander paths in a hyper-reversing field. This comes at a critical time in Earth’s history with extensive tectonic activity during the final breakup of Rodinia, substantial climatic changes after snowball Earth, and just before the onset of the Cambrian explosion of life. However, a full characterisation of the geomagnetic field has been prevented by a paucity of field strength estimates. A first ultra-weak field strength estimate at 565 Ma has been theorized to be the palaeomagnetic signal of the onset of inner core nucleation. In three multi-method palaeointensity studies, using rocks from the Grenville dyke swarm (SE Canada), the Skinner Cove volcanics (Newfoundland) and the Volyn basalt province (Ukraine), we acquired field strength estimates that suggest that the geomagnetic field may have been an order of magnitude weaker than the present-day field during the last 50 million years of the Precambrian. With this additional layer of information, the observational data can be better compared to predictions from numerical geodynamo simulations. However, due to extended data gaps in the late Precambrian and early Phanerozoic, the context of the anomalous palaeomagnetic directions and extremely weak palaeointensities is still unclear to this day.
The anomalous geomagnetic field at the Ediacaran-Cambrian transition – how much do we really know?
by Daniele Thallner
From the University of Florida
Hosted by Annique van der Boon
Published Sep. 15, 2022 10:49 AM - Last modified Oct. 17, 2022 5:22 PM