Luminescence dating of sediments from Underhoull and Lund, Unst, Shetland

This report concerns optically stimulated luminescence (OSL) investigations of sediments from the the foreshore at Burga Sands, Underhoull, and a dune section at Lund, in south-west Unst (Shetland). Samples were collected in February 2016 to establish the timing of sand accumulation, adding to an expanding set of dated sand blows in the Northern Isles and Scotland. The resulting chronologies define the local environmental record of sand movements in the vicinity of Underhoull and Lund, with their adjacent Norse longhouses and chapel. The sediment stratigraphies on the foreshore of Burga Sands were explored through four profiles, comprising the natural accumulations adjacent to two noosts (profiles 1 and 2), and the substrate sequences immediately beneath the noosts (P3&4). The dune section at Lund was explored in a single profile (P5). This report describes the progression from fieldwork and sampling, through initial luminescence screening measurements made with the portable OSL reader (on 45 samples), to subsequent calibrated analysis in the laboratory, first, to characterise the OSL and IRSL signals from each sample, then by targeted quantitative OSL dating on a further set of 10 samples. The ‘field profiles’ provided the first indication that the substrate stratigraphies at Underhoull, extend from the late glacial period to the modern day. The maxima and dynamic ranges in signal intensities for the sequences beneath the noosts, suggest that the construction and modification of these structures were temporally distinct. For the Lund section, the range in signal intensities through these sediments, indicate a shorter chronology, which was confirmed by subsequent characterisation of the profiling samples in the laboratory. The following chronology was obtained for the Underhoull section: 1) onset of sand activity, as recorded in the sedimentary archives of profiles 1 and 2, at 3.22 ± 0.29 ka (1210 ± 290BC; SUTL2861) and 1.99 ± 0.15 ka (AD30 ± 150; SUTL2863) 2) modification and re-build of the first noost at 0.48 ± 0.06 ka (AD1540 ± 60; SUTL2866) 3) construction of the second noost at 0.81 ± 0.07 ka (AD1210 ± 70; SUTL2867) 4) continued sand movements into the early 20th century AD (0.12 ± 0.06 ka; AD1900 ± 60; SUTL2862), with arguably heightened activity at the onset of the Little Ice Age (0.64 ± 0.10 ka; AD 1380 ± 60; SUTL2866). For the Lund dune section, the sediment chronology spans from the early 14th century AD through to the early 18th century AD (0.70 ± 0.05 ka; SUTL2868, through 0.52 ± 0.04 ka; SUTL2869, to 0.31 ± 0.02 ka; SUTL2870), corresponding with the onset and waning stages of the Little Ice Age. The chronology presented here is consistent with an emerging regional framework of sand movements in the Northern Isles and Scotland, with activity in the Neolithic, Early and Late Bronze Ages, the Iron Age, the Viking/Medieval period, and Little Ice Age. The Underhoull section dated here provides a broad chronology for sand blow and, importantly, places sediments underneath two noosts into the late Norse/ Mediaeval period. The dune section dates a high resolution local record within the last 700 years. Opportunities to extend the high resolution palaeoenvironmental record were identified in the adjacent land and dune-scape, and especially in the palaeo-loch landward of the Lund section, which has received sand in the past