1. IDEES UMR 6266 CNRSUniversity of Rouen Normandy Mont Saint‐Aignan France
2. British Geological Survey Keyworth Nottingham NG12 5GG UK
3. M2C Laboratory UMR 6143 CNRSUniversity of Rouen Mont Saint‐Aignan France
4. Centre Normand d'Étude du Karst (CNEK) Rouen France
5. Geomagnetism LaboratoryUniversity of Liverpool Liverpool L69 7ZE UK