Water Meadows, Silbury, Wiltshire: Optical Stimulated Luminescence Dating
Author(s): H M Roberts
Five OSL samples were taken from the palaeochannel deposits located in the Water Meadows south of Silbury Hill, Wiltshire. The depositional nature of the sediments sampled requires coarse (ie sand-sized) grains to be used for OSL dating, to ensure that the De distribution can be examined and hence that an assessment can be made whether the sediments were incompletely bleached at deposition. However, the palaeochannel sediments were all heavily dominated by clay. The coarsest of the five OSL samples taken was therefore selected to investigate the feasibility of isolating sufficient pure coarsegrained quartz for OSL dating from these clay-rich samples. Only 0.02% of the initial very large [~1kg] initial sample mass was found to be coarse-grained quartz of between 90–250µm diameter. Nevertheless, the luminescence characteristics of this material indicated that this coarse-grained quartz was suitable for dating using small aliquots. The coarse-grained quartz proved sufficiently sensitive to enable well-resolved dating using the Single-Aliquot Regenerative dose (SAR) measurement protocol applied to small multiple-grain single-aliquots. The final OSL age generated for sample 183/SR6 places the time of deposition for this material at 9770 ± 580 years ago (datum 2011), during the early Holocene. Following the completion of the pilot analysis of Water Meadows sample 183/SR6 which is the subject of the main report, the remaining four OSL samples (183/SR1–4) were prepared and analysed in an additional phase of the project. Again, using small multiplegrain aliquots of quartz, the samples studied proved sufficiently sensitive and responsive to facilitate well-resolved dating using OSL. The final OSL ages generated for the samples (reported in the Addendum) show that samples 183/SR1–4 are all significantly younger than sample 183/SR6 (discussed in the main report), giving ages that are in chronostratigraphic order (within errors) and ranging from 1200 ± 60 years ago for the lowermost clay-rich unit (sample 183/SR4) to ~
- Report Number:
- 42/2012
- Series:
- Research Report
- Pages:
- 27
- Keywords:
- Excavation Luminescence Dating
