Anisotropy of magnetic susceptibility as a tool for recognizing core deformation: reevaluation of the paleomagnetic record of Pleistocene sediments from drill hole OL-92, Owens Lake, California

Abstract

At Owens Lake, California, paleomagnetic data document the Matuyama/Brunhes polarity boundary near the bottom of a 323-m core (OL-92) and display numerous directional fluctuations throughout the Brunhes chron. Many of the intervals of high directional dispersion were previously interpreted to record magnetic excursions. For the upper ∼120 m, these interpretations were tested using the anisotropy of magnetic susceptibility (AMS), which typically defines a subhorizontal planar fabric for sediments deposited in quiet water. AMS data from intervals of deformed core, determined from detailed analysis of sedimentary structures, were compared to a reference AMS fabric derived from undisturbed sediment. This comparison shows that changes in the AMS fabric provide a means of screening core samples for deformation and the associated paleomagnetic record for the adverse effects of distortion. For that portion of core OL-92 studied here (about the upper 120 m), the combined analyses of sedimentary structures and AMS data demonstrate that most of the paleomagnetic features, previously interpreted as geomagnetic excursions, are likely the result of core deformation.