Magnetostratigraphic studies have been undertaken on sedimentary continental formations from Western France and Spain which have yielded Palaeogene mammals. The results obtained provide new constraints on the chronological distribution of the mammalian reference levels. A magnetozone sequence associated with the reference levels is defined. The correlation of this sequence with the geomagnetic polarity time scale is proposed. This correlation links the late Mid-Eocene to Oligocene mammalian biochronological scale from Western Europe to other stratigraphic scales.
A numerical calibration of the Palaeogene polarity sequence is made, taking into account recent radiometric dating. The equations to convert the ages proposed by several authors are given.