The Nature of the Ediacaran to Early Cambrian Geomagnetic Field

English Abstract:

A rotation of the entire solid Earth by 90°, in what has been called an inertial interchange true polar wander (IITPW) event, has been linked to the significant increase in biotic diversity during Ediacaran to early Cambrian (~635-530 Ma) times. Evidence for the IITPW event has been suggested by previously reported nearly orthogonal directions from the Sept-Îles (ca. 565 Ma) intrusion (Quebec, Canada) on the basis of whole rock analyses. We have demonstrated that only one direction (shallow) is carried by single domain magnetic grains and thus can be considered primary (Bono and Tarduno, Geology, 2015). Moreover, we find that the geomagnetic field was reversing during cooling of the intrusion; the small spatial scales on which we see antipodal directions suggest a rapid reversal rate. New Total Thermoremanent Magnetization paleointensity experiments on single feldspar crystals from the Sept-Îles intrusion imply a very low field value, somewhat lower than values recorded by single feldspars from Jurassic basalts (Tarduno and Cottrell, JGR, 2005). The high geomagnetic reversal rate and low geomagnetic field intensity that characterize a portion of the Jurassic (ca. 165 Ma) may be an analog for field behavior during the Ediacaran to early Cambrian. We will discuss further paleointensity experiments aimed at testing this hypothesis.