Measuring heterogeneous remanence in paleomagnetism

Abstract

Remanence directions of from the same block-sample may be inconsistent or unrepresentative due to orientation and location heterogeneity of their remanence-bearing minerals (RBM). Magnetization-heterogeneity is usually undetectable at the specimen-level but we replicated its effects by measuring 8 small specimens with stable magnetizations (8 or 5.2 cm3). These were assembled into a single large multi-specimen inside 125 cm3 containers that were measured in a Molspin "BigSpin" magnetometer. Large-specimen remanence directions deflect towards the direction of any strongly magnetized sub-specimen. Differences between the large-specimen remanence and that for the group of individually measured sub-specimens worsened when one sub-specimen was mis-oriented. These discrepancies were cancelled or reduced using larger numbers of specimen orientations in the magnetometer. Conventional schemes with 4 or 6 different measurement-orientations may fail to suppress heterogeneity-effects whereas our 12-orientation protocol may succeed. For most specimens, acceptable remanence-homogeneity is present where similar remanence-directions are recorded from 4, 6, and 12 different spin-orientations. Copyright 2007 by the American Geophysical Union.