Holocene geomagnetic paleointensities: A blind test of absolute paleointensity techniques and materials

Abstract

Through several decades of research, absolute paleointensity estimates have been obtained from a wide range of rocks with varying ages, covering the last 3.45 Ga years. These paleointensity data are crucial to study the past geodynamo and the geological evolution of the Earth's deep interior. However, paleointensity data are often difficult to interpret, and on-going discussions concerning the past geomagnetic field invariably focus on data reliability, and which kind of material, and method, is best suited for absolute paleointensity experiments. In this paper we blind test paleointensity methods and materials using the new GEOMAGIA50 database that contains all available experimental information about published paleointensity estimates covering the last 50,000 years. Our analysis is built on simple comparisons of results obtained from different materials, and methodologies, to investigate their possible influence on the paleointensity estimate. We also study the effect of various numbers of samples, and dating accuracies. We focus on paleointensity estimates from the last 12,000 years, which includes the Holocene epoch. The advantage of this period is that data have been obtained from a wide array of methodological techniques as well as a wide selection of materials, including both natural ones (e.g. lava flows) and various archaeological artifacts. Our main observations are (i) that well-fired archaeological materials (bricks, potteries, clays, and ceramics) show the best correlation with the rest of the dataset, which we interpret to suggest that these data are the most reliable, and (ii) although paleointensity data obtained from lava flows are slightly more scattered, there is no evidence for paleointensity data from lavas to be significantly lower or higher than other data, irrespective of the methodology.