Palaeomagnetic results from sediments of the Perth Basin,Western Australia,and their bearing on the timing of regional lateritisation

In an attempt to extend palaeomagnetic investigation of Late Palaeozoic and Mesozoic rock formations in Australia, 222 oriented samples have been collected from sedimentary horizons in the Perth Basin and adjacent areas. The thermal stability of the remanent magnetism has been established, but its direction remained oriented close to the direction of the present local geomagnetic field, irrespective of the age of formation sampled. Further attempts to partially demagnetise some specimens using chemical techniques also failed to isolate the primary component of magnetisation. The results have been interpreted as indicating an episode of “blanket” remagnetisation which occurred during the period of regional lateritisation. The presence of normal and reversed polarities indicates that remagnetisation occurred over an extended period of time. By comparing the paleomagnetic pole positions with the apparent polar-wander curve recognised for the Cenozoic of Australia, quantitative support for a Late Oligocene to Early Miocene age for the period of lateritisation is given. Other palaeomagnetic evidence suggests this age may be correlated to laterites in Northern Territory.