Sequential geomagnetic reversals recorded in Upper Tortonian marine clays in western Crete (Greece)

We report a very detailed study of four different geomagnetic reversals of upper Tortonian age, recorded in three marine sections in western Crete. Multiple records have been obtained for two of the reversals, and both the directional and the relative field intensity behavior have been studied. The intensity decreases to about 15% of its pretransitional value in all cases. For the three oldest reversals the sequences of changing field directions of reversals of opposite sense are almost antipodal, suggesting that the process of reversal from either starting polarity stays unchanged for about 1.3 m.y. A change then occurs for the fourth reversal. The occurence of perturbations in the sequence of changing field directions in two records either at the onset or at the end of the reversal are interpreted in terms of a recently suggested mechanism for triggering reversals.