Effect of magnetic anisotropy on the natural remanent magnetization in the MCU IVe' layer of the Bjerkreim Sokndal Layered Intrusion, Rogaland, Southern Norway

A strong negative magnetic anomaly, caused by an intense natural remanent magnetization (NRM) approximately opposite today's geomagnetic field, is observed above the MCU IVe' unit of the Bjerkreim Sokndal Layered Intrusion. The anomaly is strongest in the east, close to Heskestad, and decreases when following the layer toward the north and west. This study investigates how the NRM changes along the layer and how its direction and intensity are affected by magnetic fabrics in the intrusion. NRM, low-field anisotropy of magnetic susceptibility, and anisotropy of anhysteretic remanence have been measured on 371 specimens from 46 sites. The orientation of both the magnetic fabrics and the NRM changes for different locations along the layer, and it appears that the NRM is tilted away from the mean paleofield and toward the direction of maximum susceptibility and maximum anhysteretic remanence. When NRM directions are corrected for magnetic fabrics, the angle between the NRM and mean paleofield direction generally decreases for specimens with a single-component NRM. No correlation was found between the NRM intensity and the directional relationship between NRM, magnetic fabric, and mean paleofield.