An archaeomagnetic investigation of a Roman amphorae workshop in Albinia (Italy)

Abstract : An intensive archaeomagnetic investigation of an Italian Roman amphorae workshop has been carried out in order to produce high quality data to enhance the European archaeomagnetic database. Additionally, and importantly, this study also investigates within and between structure variations and, the influence of anisotropy and cooling rate corrections. Eighty-six oriented samples were taken from five kilns for full geomagnetic vector (directions and intensity) determination. Additionally, cores from 39 amphorae found at the site were drilled for archaeointensity analysis. The site is archaeologically dated as being between 2nd century BC and 1st century AD, and the amphorae as being 1st century BC. A full suite of rock magnetic experiments were carried out which indicate the samples' suitability for archaeointensity experiments. The classical Thellier method with correction for anisotropy of thermal remanence (TRM) was used to determine the direction of the characteristic remanence and the archaeointensity. Differences between fast and slow cooling during remanence acquisition were investigated and a cooling rate correction applied to the archaeointensity estimates. After correction for anisotropy of TRM, the scatter about the kiln (amphorae) mean value is reduced and the scatter between kilns is also reduced for both directions and archaeointensity, demonstrating the necessity of carrying out the anisotropy of TRM correction for these samples. Application of the cooling rate correction results in a decrease in archaeointensity as expected on theoretical grounds for single domain grains. The correction, whilst not reducing scatter in the mean archaeointensity results, does result in a reduction in the scatter found between the kilns. The directional results are compared to the French, and a preliminary Italian, secular variation (SV) curve and suggest that the kilns may be towards the older limit of the archaeologically given age however the master curves are not well constrained in this time interval. Instead, the five new directional data should be used to help constrain future curves. The Albinia archaeointensity data are consistent with the broad trends seen in the limited high quality Western European and Mesopotamian data sets and with the newly constructed archaeointensity SV curve for Greece. Similar to other studies whilst the archaeointensity results for each kiln (the amphorae) are well constrained (4-7 per cent scatter about the mean) variations are seen between the kilns (mean archaeointensity 62-70 mu T). This further supports the suggestion that it is necessary to obtain a number of archaeointensity data for each time interval in order to reliably record variations of the Earth's magnetic field from archaeological material. The archaeointensity result for the set of amphorae which has the better constrained age falls within the archaeointensity values from the kilns. Combining the results from the five kilns and the amphorae gives a mean archaeointensity of 64 +/- 3 mu T at Albinia (69 +/- 3 mu T relocated to Paris) during 200 BC-100 AD.
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Mimi Hill, Philippe Lanos, Annick Chauvin, Daniele Vitali, Fannette Laubenheimer. An archaeomagnetic investigation of a Roman amphorae workshop in Albinia (Italy). Geophysical Journal International, Oxford University Press (OUP), 2007, 169 (2), pp.471-482. ⟨10.1111/j.1365-246X.2007.03362.x⟩. ⟨insu-00155118⟩

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