The evolution of a Mid-Miocene geomagnetic reversal

The Earth's magnetic field reverses its polarity non-periodically. Despite the large number of reversals in the magnetostratigraphic record, the geometry of the Earth's magnetic field and the mechanisms driving reversals are still largely enigmatic. On the one hand, this is because the more readily available sedimentary records lack temporal resolution to record the rapid field changes during a reversal, and on the other hand because the volcanic data records -that may have the necessary temporal resolution- are dependent on volcanic eruption frequency and much more difficult to find. Here we produce a geomagnetic record with high temporal resolution that formed during the shield-building phase on Gran Canaria, Spain. Furthermore, we provide five radio-isotope age constraints for the section containing a mid-Miocene geomagnetic reversal. Our full-vector geomagnetic record is one of the most detailed records of a reversal to date. Surprisingly, we find that in the most reliable part of our record of the reversal the declination reverses only once, while the inclination flips at least five times. Lastly, we interpret this record as a combination of a geocentric axial dipole and non-axial dipole fields and show that the contributions of the non-axial dipole field can be relatively strong.