A TEST OF THE GEOCENTRIC AXIAL DIPOLE HYPOTHESIS FROM AN ANALYSIS OF THE SKEWNESS OF THE CENTRAL MARINE MAGNETIC ANOMALY

A new, global set of palaeomagnetic observations was obtained from ana lysis of the symmetry of the shape of 203 crossings of the Central mar ine anomaly, the anomaly observed above seafloor, formed during the Br unhes normal polarity chron (0-0.78 Ma). The data indicate that the ti me-averaged field can be described best by a dominant geocentric axial dipole component, whose position differs insignificantly from the pre sent spin axis, and by a small geocentric axial quadrupole component ( 6.0%(+5.7%)(-6.7%) the size of the dipole component). If we simply ass ume that the Brunhes palaeomagnetic axis has been aligned with the pre sent spin axis, the quadrupole component is 6.2% +/- 4.7%, which diffe rs significantly from a purely dipolar field, and is in good agreement with estimates from other palaeomagnetic data. Besides expanding the spatial distribution of palaeomagnetic field observations, an importan t step in removing biases in prior field estimates caused by poor glob al coverage, these results illustrate that valuable geomagnetic inform ation as well as accurate palaeomagnetic poles can be obtained from sk ewness data.