Ediacaran paleomagnetic field records from Laurentia: Insights into the evolution of the diversity of life and Earth’s deep interior

Abstract:

The Ediacaran to early Cambrian interval (~635-530 Ma) marks a tremendous increase in biotic diversity known as the Cambrian explosion. The magnitude of the biotic evolution has motivated hypotheses evoking a role for abiotic/environmental causal factors. For example, 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 these events. One of the primary data sets motivating IITPW has been the report of nearly orthogonal directions from the Sept-Îles (ca. 565 Ma) intrusion (Quebec, Canada) on the basis of whole rock paleomagnetic analyses. We have found that only one direction (shallow) from our sampling of the Sept-Îles intrusion 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 very rapid reversal rate. Preliminary total-TRM paleointensity results from the Sept-Îles intrusion suggest a low field strength. 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. This model may provide insight into the development of Earth’s interior; if high thermal core conductivity values are correct, the onset of inner core growth is predicted to have an age similar to that of our directional and paleointensity data. To test these linkages, we investigate dated localities of the Grenville dikes (ca. 590 Ma) from which classic paleomagnetic results on whole rocks (Murthy, 1971) have long figured into debates over the paleolatitude history of Laurentia. New rock- and paleo-magnetic experiments testing single crystal feldspars from Laurentian Ediacaran intrusive units will be discussed, along with new estimates of geomagnetic field intensity prior to the Cambrian.