OSL dating of the Mesolithic site Nilsvikdalen 7, Bjorøy, Norway.

Sammanfattning: Luminescence dating is a well-established dating method within geological and archaeological research. However, the use of luminescence dating, and more specifically optically stimulated luminescence (OSL), is currently underutilised in Norwegian archaeology. This study set about determining the suitability of this dating method as a viable option for excavations of Norwegian coastal Stone Age sites. This is done by OSL dating six samples from three superimposed cultural layers at a settlement (Nilsvikdalen 7) at Bjorøy, SW Norway, which has previously been radiocarbon dated to the Late Mesolithic period, and subsequently evaluating the method suitability from the results. The cultural layers all consist of varying degrees of humus-rich sand with charcoal, where OSL samples were taken from inside and outside an interpreted hut structure. Quartz OSL dating was carried out using the Single Aliquot Regenerative-dose (SAR) protocol for all six samples and yielded successful results. The samples displayed a strong quartz signal with excellent characteristics. The water content of the site yielded the highest uncertainties for the dose rate determination and was after thorough evaluation determined to ~ 63 – 114%. Dose rate was determined to ~ 2 – 4 Gy/ka. Different age models were applied, where the mean age was chosen for the final age determination. The bottom cultural layer was dated to the Late Mesolithic, with OSL ages of 8.07 ± 0.51 ka and 7.02 ± 0.43 ka inside the hut, as well as 6.60 ± 0.40 ka outside the hut boundary. The middle and upper layers were dated to Late Mesolithic – Early Neolithic, where the middle unit displayed an age of 6.25 ± 0.36 ka and the upper layer yielded ages of 5.56 ± 0.32 ka and 6.94 ± 0.36 ka (all dates inside the hut). Three of the samples overlap with the corresponding radiocarbon dates, whilst the other three do not statistically agree (values outside of ± 2 σ) with the radiocarbon dates. For the samples without statistical agreement, the OSL ages produced are younger than the corresponding radiocarbon dates. For future OSL dating it is suggested to, if possible, take a control sample of recent or known age from a site area to reduce possible uncertainties in the luminescence age determination process. Given the successful dating of the Nilsvikdalen 7 site, this project demonstrates how OSL dating could provide a good solution for future dating of Norwegian coastal Stone Age sites.