Mineral magnetism and archaeomagnetic dating of a mediaeval oven from Zlatna Livada, Bulgaria

Archaeomagnetic palaeodirectional and palaeointensity results are presented from a domestic oven at the mediaeval site of Zlatna Livada. Archaeological evidence suggests that the site was occupied in the 11th or 12th C. AD, with the oven dating to the beginning of this period. The samples are dominated by magnetite and maghaemite. In some samples thermally unstable maghaemite occurs with unblocking temperatures between 300 °C and 400 °C, while in others maghaemite is stable to inversion until >600 °C. The mineral magnetic analyses, Thellier results and sample heterogeneity suggest that the oven was not heated to a very high or consistent temperature in antiquity (<320-<400 °C). Hysteresis measurements show a mixture of single and multi-domain grains, which may account for the variability in the success of the Thellier experiments. Water glass, the material used to physically stabilize unconsolidated samples, does not appear to react with the samples' mineralogy until above 500 °C, and thus does not affect the Thellier results. The oven has a mean palaeointensity determination of 72.13 μT, a mean declination of 15.8o and a mean inclination of 61.9o. The archaeomagnetic age estimate for the site using all three parameters is between 826 and 1004 AD and using only palaeodirectional data is 777-967 AD. Based on these archaeomagnetic age assessments and the archaeological evidence, the site is best dated to the very end of the 10th C. AD or first few years of the 11th C. AD. This confirms that the oven dates to the early period of site use, although the date is perhaps slightly younger than expected. This paper highlights a number of problems encountered during archaeomagnetic studies and emphasises the need for more reference curve data to increase the precision of the dating method, particularly during the mediaeval period in Bulgaria.