Tim’s contribution to this project involved the construction of the sediment chronologies for the sand sequences associated with the Norse Settlement site at Sandwich South, Unst (Sheltland Isles), which record accumulations of blown-sand, potentially linked to climatic instability. These young sediments, with low sensitivity and low dose rates, presented challenges for luminescence dating. Field gamma dose rates below 0.1 mGy a-1, and total dose rates of 0.4-0.5 mGy a-1, combined with expected ages of less than 1 ka, resulted in a requirement for quantitative determination of equivalent doses of 0.2-0.4 Gy.
The featured publication, Feldspar SARA IRSL dating of very low dose rate aeolian sediments from Sandwick South, Unst’, documents the approaches developed to date these challenging, young insensitive materials. The reconciliation of HRGS data, converted to infinite matrix dose rates, with measured beta and gamma dose rates, counted over extended periods and in duplicate, enabled total environmental dose rates to be estimated with less than 6% uncertainties. The modified SARA approach, which incorporates a long overnight preheat before first measurement, yielded archaeologically meaningful ages, concordant with independent age controls. The dates demonstrate sand accumulation in the early to mid-13th century AD and also in the 18th century AD, which are contemporary with disruptive sand movements registered in other coastal regions of the Northeast Atlantic and North Sea regions.