1. Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands
2. Current address: Dublin Institute for Advanced Studies, Geophysics Section, 5 Merrion Square, Dublin 2, Ireland
3. Université Rennes 1, Géosciences Rennes UMR 6118 CNRS, Campus de Beaulieu, 35042 Rennes, France
4. Paleomagnetic Laboratory ‘Fort Hoofddijk’, Faculty of Geosciences, Department of Earth Sciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands