Palaeomagnetic Results from the Gordon Subgroup of Tasmania: Further Evidence for a Late Cretaceous Magnetic Overprint in Southeastern Australia

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 = l . 3o, N = 92 South pole position 59.8°5 1 41.1°E, dp = 2 . 4°, dm = 2 . 5°)during Late Cretaceous or less likely Early Tertiary time . This finding further supports a recently recognized Late Cretaceous remagnetization event in southeastern Au stral ia ,which is attributed to r ift forming processes preceding the opening of t he Tasman Sea. Conodont colour indicates that the limestones studied have not been subjected to temperatures in e xcess of l00°c . This suggests a possible widespread occurrence of this magnetic overprint.