Recent advances in fine particle magnetism: Implications for paleomagnetism

Abstract

It is becoming increasingly obvious in paleomagnetism that the older practice of using large numbers of samples to improve statistical measures of accuracy is often not adequate to reveal the signal of greatest geological importance. “Blanket” demagnetization treatments are now largely outdated, except for the most ideally behaved samples (a rapidly vanishing phenomenon in many locales). Variations in characteristic remanent directions between neighboring (and supposedly contemporaneous) but lithogically distinct rock units can no longer be simply treated as “noise”. We now recognize that such differences may actually reflect rock magnetic effects rather than such factors as the short‐term behavior of the geomagnetic field or local variations in structure. Multiple overprints, often the result of moderate reheating and/or chemical alteration, can result in an uncertain relationship between the timing of emplacement and the acquisition of remanence. In the past, rocks which presented such problems could often be avoided in favor of more straightforward units. Much of that geological “cream” has been skimmed, however. Further progress in many areas, particularly the determination of the APW path and reversal stratigraphy in the Paleozoic, will require a better understanding of magnetization processes in order to resolve the above‐mentioned problems and produce accurate and reliable results.