Abstract
Archaeomagnetic dating offers a valuable chronological tool for archaeological investigations, particularly for dating fired material. The method depends on the establishment of a dated record of secular variation of the Earth's magnetic field and this paper presents new and updated archaeomagnetic directional data from the UK and geomagnetic secular variation curves arising from them. The data are taken from publications from the 1950's to the present day; 422 dated entries derived from existing archaeo and geomagnetic databases are re-evaluated and 487 new directions added, resulting in 909 entries with corresponding dates, the largest collection of dated archaeomagnetic directions from a single country. An approach to improving the largest source of uncertainty, the independent dating, is proposed and applied to the British Iron Age, resulting in 145 directions from currently available databases being updated with revised ages and/or uncertainties, and a large scale reassessment of age assignments prior to inclusion into the Magnetic Moments of the Past and GEOMAGIA50 databases. From the significantly improved dataset a new archaeomagnetic dating curve for the UK is derived through the development of a temporally continuous geomagnetic field model, and is compared with previous UK archaeomagnetic dating curves and global field models. The new model, ARCH-UK.1 allows model predictions for any location in the UK with associated uncertainties. It is shown to improve precision and accuracy in archaeomagnetic dating, and to provide new insight into past geomagnetic field changes.
Highlights
The development of precise, robust site chronologies is a central concern in all archaeological work and there are a range of scientific dating methods available to address this issue
The Earth's magnetic field in the past can be recorded by fired archaeological materials or sediments and a date is obtained for this geomagnetic record by comparison with a dated record of changes in the geomagnetic field over time, known as the secular variation (SV) record
Radiocarbon determinations were only considered if they could be closely related to the event that caused the geomagnetic field to be recorded or when there was a stratigraphic relationship between the radiocarbon determination and the context sampled for archaeomagnetic studies, in which case Bayesian methods of analysis using Oxcal (Bronk Ramsey, 2009) were employed (Fig. 1a)
Summary
The development of precise, robust site chronologies is a central concern in all archaeological work and there are a range of scientific dating methods available to address this issue. Archaeomagnetic dating is a valuable addition to the suite of chronological tools available to archaeologists working on both commercial and research excavations. The aim of this paper is to present new and re-evaluated UK archaeomagnetic data and the geomagnetic secular variation curves arising from them. Such discussions are uniquely important in archaeomagnetic dating as the precision and accuracy of dates provided by the method improve as more data are used in the construction of dating curves. Archaeomagnetic studies have a wider significance as they provide the most detailed record of how the geomagnetic field has changed over recent millennia; crucial to understanding deep Earth processes, the space environment, palaeoclimate and volcanism (Brown et al, 2015a; Constable and Korte, 2015)
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