GEOMAGNETIC-FIELD STABILITY - REVERSAL EVENTS AND EXCURSIONS

It has been suggested that there are several reverse subchrons in the Brunhes, and this suggestion is gaining some acceptance. However, such a suggestion has fundamental implications for the reversal process, b ecause it implies that the reverse polarity state has been substantial ly less stable than the normal polarity state during the Brunhes Chron . Analysis of the latest polarity reversal timescale confirms that the re is no reason to reject the hypothesis of a common stability for the two polarity states. The Cretaceous Superchron appears to be a time w hen the reversal rate slowed to the point where the reversal process a ctually halted, so does not indicate any difference in the stability o f the two polarity states. After examining the data we found no convin cing evidence for even a single reversal event during the Brunhes, and we conclude that the only reversal excursions that are sufficiently w ell documented for the Brunhes are the Laschamp and the Blake, Further , we note that the question of whether of large excursions represent a borted reversals is unresolved, so excursion data should not at this s tage be grouped with transition polarity data. Finally, we note that, most of the time, the nearly axially symmetric normal and reverse pola rity states appear to be remarkably stable.