A method for the removal of rotational remanent magnetization acquired during alternating field demagnetization

Abstract

Experimental evidence has confirmed the existence of rotational remanent magnetization (RRM), a spurious remanence imparted to rock specimens that have been rotated in a decreasing alternating field. Sediments with low magnetic stability systematically acquired RRM while being demagnetized in fields of 50-200 Oe. Our results were obtained from demagnetization equipment utilizing a four-axis specimen holder. When a demagnetization run was repeated in the same peak field, but with the specimen holder's direction of rotation reversed, RRM was created that was equal and opposite to the RRM of the previous run. The spurious magnetization can be removed by averaging the paleomagnetic vectors obtained from two demagnetization runs carried out with forward and backward rotations of the specimen. Besides removing RRM, doubledemagnetization is desirable because it gives an estimate of the directional dispersion due to random noise in the applied field, and thus provides a check on the reproducibility of the AF treatment.