| Popis: |
We report on a high resolution transition record from Searles Valley, California that appears not to be hampered by problems of smoothing or recording breakdown, and, unlike many other sedimentary records, defines a path unconfined in longitude. A prominent feature of the record is the steady oscillation of the pole along a swath stretching from west Africa across north Eurasia to the northwest Pacific. The endpoints of the swath are associated with a change between steady and rapid field variation, consistent with results for an older transition from a nearby volcanic record. The transition culminates with poles migrating from west Africa to South America, midway between the two earlier-proposed longitudinal bands. This path indicates the reversing field has either a wider spectrum of behavior than recently suggested or is described by a more complicated field geometry than one dominated by an equatorial dipole or strong low-order nondipole component. From a comparison with existing records from the same general geographic area, we address the significance of the swath, the lack of longitudinal confinement, patterns of steady and rapid field changes, and the temporal persistence of these features in relation to the geometry of the reversing field. |
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