Estimates of the Earth's spin (geographic) axis relative to Gondwana from glacial sediments and paleomagnetism

The ice centres of the Permo-Carboniferous and late Ordovician glaciations of Gondwana have been quantitatively estimated. Their positions relative to the inferred mean paleomagnetic poles are not significantly different from those of the Quaternary ice centres relative to the present-day geographic poles. These data suggest it is unnecessary to postulate that the Paleozoic Earth had marked non-dipole components in the geomagnetic field, or that the average of the dipole axis was significantly different from the geographic axis or that there was a significantly different tilt to the geographic axis. The short-lived late Ordovician ice age is tentatively attributed to equally short episodes of faulting within Gondwana. These are believed to have created transient highlands which converted a previously snow-free summer climate into one in which snow could accumulate and build ice caps. Once the faulting ceased the topography decayed and the climate reverted to its previous snow-free summer state. Keywords: tillites; ice ages; paleomagnetism; Gondwana; Paleozoic; Ordovician; Permo-Carboniferous