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 = 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 Australia , which is attributed to rift forming processes preceding the opening of t he Tasman Sea. Conodont colour indicates that the limestones studied have not been subjected to temperatures in excess of l00°c . This suggests a possible widespread occurrence of this magnetic overprint.