Tests of Magnetic Properties of New Zealand Pliocene Marine Mudstones

Abstract

Three tests have been used in a magnetostratigraphic investigation of Pliocene mudstones in the Wanganui Basin of New Zealand to examine the viscous behaviour and the stability of secondary overprints, including those acquired after sampling. A storage test evaluated longer term viscosity. The other tests measured remanent magnetization acquired during drying and short term viscosity. The results of these tests have led to the adoption of the following procedures for collecting and handling palaeomagnetic samples: 1. Sampling sites are located to provide fresh, unweathered samples from saturated sediments that have never dried out. 2. Samples are stored moist and unshielded until sample preparation is complete. 3. The specimens are then dried in mumetal shields and stored shielded until measurements are finished. These procedures permit reliable determination of reversed and normal palaeodirections from all but the most unstable specimens.