A negative test of orbital control of geomagnetic reversals and excursions

A similar to 41 Kyr periodic component has been reported in some sedimentar y paleointensity records, allowing speculation that there may be some compo nent of orbital control of geomagnetic field generation such as by obliquit y modulation. However, no discernable tendency is found for astronomically- dated geomagnetic reversals in the Plio-Pleistocene (0 to 5.3 Ma) or excurs ions in the Brunhes (0 to 0.78 Ma) to occur at a consistent amplitude or ph ase of obliquity cyclicity, nor of orbital eccentricity. An implication is that paleointensity lows which are characteristically associated with these features are not distributed in a systematic way relative to obliquity and eccentricity, supporting the idea that orbital forcing does not power the geodynamo.