Palaeomagnetic dating of Late Cretaceous to Early Tertiary weathering in New England, N.S.W., Australia

Palaeomagnetic dating of Australia's regolith is becoming more refined with advances in techniques and better definition of the Late Mesozoic and Cenozoic apparent polar wander path of Australia. The suspected great antiquity of parts of the regolith is being confirmed through the application of palaeomagnetic dating to authigenic iron oxides which form during weathering. Earlier palaeomagnetic investigation tentatively suggested that deeply weathered volcanics in the New England area formed in the Mesozoic, implying that ideas regarding the palaeoenvironment of New England may need considerable revision. Published dates for other, unweathered, volcanics from this area are K-Ar ages of 21.8 Ma, 32.8 Ma and 25.1 Ma. The earlier palaeomagnetic conclusions were based on results from only one (the Sugarloaf) of the seven separate localities (nine sites) originally sampled, these results being the only results that were internally consistent. Follow-up work using a high sensitivity cryogenic magnetometer has now yielded consistent results from the six other localities which support those from the Sugarloaf, but a revised weathering age of about 60 Ma seems more likely. This age is virtually identical to that determined for the Morney Profile in southwestern Queensland.