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Abstract: Lake sediments can play an important role in understanding and reconstructing temporal characteristics of the geomagnetic field, as they potentially offer near continuous high-resolution archives of magnetic information extending throughout the Holocene. To date lake sediment geomagnetic data has typically been excluded from British archaeomagnetic secular variation curves (SVC) due to uncertainties with the acquisition of magnetisation by lake sediments. This paper presents the argument that, with regards to British datasets, the real problem lies with poor chronological control and sets out to illustrate that with British archaeomagnetic data some progress has been made. The results indicate that it is not currently possible to resolve secular variation on a time scale of ∼100years from published British lake sediment data but more success has been made with data from archaeological sediments. This level of detail has been considered necessary for the incorporation of lake sediment data into the British archaeomagnetic dataset, as the ability to resolve short-term geomagnetic changes is critical for the integration of any dataset into the British SVC. As the latter is predominantly employed to date archaeological architecture and artefacts requires that it has the ability to resolve changes over timescales relevant to human lifetimes. Using currently available data this retrospective critique confirms that, in archaeological sediments, depositional and thermoremanent magnetisation can record the same direction over the same time interval. [Copyright &y& Elsevier]

Abstract: Through several decades of research, absolute paleointensity estimates have been obtained from a wide range of rocks with varying ages, covering the last 3.45Ga 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. [Copyright &y& Elsevier]