Palaeomagnetic results from the Gordon Subgroup of Tasmania: further evidence for a Late Cretaceous magnetic overprint in southeastern Australia

Abstract

A thermal demagnetization study of 48 limestone samples from the Ordovician Gordon Subgroup of Ida Bay (Tasmania), indicated complete remagnetization (D 9.4°, I -81.4°, k = 137.5, a95 = 1.30, N 92 South pole position 59.80 S 141.10E, dp = 2.4°, dm = 2.5°) during Late Cretaceous or less likely Early Tertiary time. This finding further supports a recently recognized Late Cretaceous renagnetization event in southeastern Australia, which is attributed to rift forming processes preceding the opening of the Tasman Sea. Conodont colour indicates that the limestones studied have not been subjected to temperatures in excess of 100°C. This suggests a possible widespread occurrence of this magnetic overprint.