Geomagnetic Secular Variation During the Brunhes Epoch in the Indian and Atlantic Ocean Regions

Summary Brunhes epoch secular variation in the Indian and Atlantic Ocean regions has been examined using available and unpublished palaeomagnetic results from igneous rocks. Specimens from 401 separate units, all of which have unstable components minimized, are involved. More than half of these data are previously unpublished. The data are classified as fist order when the mean direction for each body is derived from at least four separate specimens, and second order when the number of specimens per body is not considered. Geomagnetic palaeosecular variation models are examined in terms of the latitude dependence of angular dispersion ( S ) of virtual geomagnetic poles (VGP's). Value of S from second order data, while exhibiting wide 95 per cent confidence intervals, increase with latitude. First order data also yield S values increasing with latitude, and are sufficiently well defined to indicate that S may have increased more rapidly with latitude during the Brunhes Epoch than at present. While the simple diode wobble model for the geomagnetic field is clearly excluded by the results, no distinction can be made between other current models, and the possibility of the existence of a region of attenuated Brunhes epoch non‐dipole activity in the west‐central Indian Ocean cannot be excluded.