Dating

Luminescence dating depends on the ability of minerals to store energy in the form of trapped charge carriers when exposed to ionising radiation. Stimulation of the system, by heat in the case of thermoluminescence (TL), or by light in the case of photo-stimulated luminescence (PSL), or optically stimulated luminescence (OSL).

Following an initial zeroing event, for example heating of ceramics and burnt stones, or optical bleaching of certain classes of sediments, the system acquires an increasing luminescence signal in response to exposure to background sources of ionising radiation. Luminescence dating is based on quantifying both the radiation dose received by a sample since its zeroing event, and the dose rate which it has experienced during the accumulation period. The technique can be applied to a wide variety of heated materials, including archaeological ceramics, burnt stones, burnt flints, and contact-heated soils and sediments associated with archaeological or natural events. Optically bleached materials of interest to quaternary science include aeolian, fluvial, alluvial, and marine sediments.

Luminescence dating can be applied to the age range from present to approximately 500,000 years, thus spanning critical time-scales for human development and quaternary landscape formation. Precision varies from ±3-10% of age for heated materials and ±5-20 % for sediments. Luminescence dating techniques can also be used for dose reconstruction, following accidental exposure to ionising radiation, and to assess thermal exposure for example of concrete structures subject to fire damage.

The laboratory has extensive experience of dating archaeological ceramics and burnt stones from sites in Scotland and overseas. The value of TL dating of such materials frequently lies in the association between the event being dated and an archaeologically important event in the development of the site. For example the last heating of a hearth stone dates the abandonment of a prehistoric settlement. More recently there has been a marked increase in interest in optical dating of sediments, with many groups within the Scottish Universities having application interests.

Examples of current and recent projects include:

Dating of wind-blown sands from archaeological sites in the Northern and Western Isles.This project forms a PhD study by Anne Sommerville which is supported jointly by SURRC, University of Glasgow Archeology and Geography departments. The Northern and Western Isles have an abundant set of important archaeological sites which have been affected in the past by extensive aeolian sand deposition. This project aims to establish the precision and accuracy of OSL dating of wind-blown sands from well characterised sites, and to investigate the relationships between sand deposition and regional climatic change over the last 5000 years, together with an assessment of the impact of such change on early communities.

Dating burnt stone moundsBurnt mounds are comprised heaps of fire cracked stones up to several met9 September, 2005ehistoric cooking. There are more than 1600 known sites in the National Monuments Record of Scotland, and recent archaeological work has raised questions about functions, periods, and durations of use of these monuments. The project is underway in collaboration with GU Archaeology Department, with support form EPSRC and Historic Scotland, to address some of these questions. Iona Anthony is basing her PhD research on this project.

Imaging TL and OSL from single-mineral grainsSome sedimentary systems of environmental interest produce heterogeneous mixtures of well bleached and poorly bleached material, presenting significant problems for OSL dating. Iain Houston was conducting a Msc research at SURRC, in collaboration with Professor P. Bishop, Dept. of Geography and Topographic Sciences, Glasgow University, with a scholarship from Physical Sciences Planning Unit of Glasgow University. The use of scanning techniques based on focussed lasers, to stimulate luminescence from individual mineral grains, is being investigated as a means to characterise heterogeneous systems and potentially to overcome their limitations.

Dating volcanic tephrae from North-West IcelandStephen Roberts has been working with Dr Sanderson on TL dating of volcanic ash deposits from NW Iceland as part of his PhD research in Geography at the University of Edinburgh. This work has shown that the Oþoli tephrae from Skagåfjell is of mid-Pleistocene age or earlier, and not a had previously been supposed of Holocene age. This implies that the peninsula in question in NW Iceland was ice-free during the last glaciation, which is of considerable interest in its own right. The use of TL to date vitreous material is relatively new, and this project suggests that there is considerable further potential.

Dating cover-sands from South East AsiaA series of quartz-rich cover sands from NE Thailand, which form part of a regional mantle, have been dated in collaboration with Professor P Bishop (GU Geography and Topographic Sciences). The results are supportive of a primarily aeolian deposition process over the last 40-50ka, with some evidence of bioturbational mixing in upper layers. Further work is planned.

Dating fluvial sediments associated with early agricultureAs part of a British Academy funded investigation of the origins of agriculture in the Near East, a set of fluvial and alluvial sediments from Wadi Faynan, Jordan, are being studied in collaboration with Dr. W. Finlayson (Edinburgh University) and Dr. R. Tipping (Stirling University). It is hoped that the results will elucidate the landscape formation chronology associated with an area on the fringes of the fertile crescent with important evidence of the earliest periods of agriculture.

Dating deltaic sediments from AntarcticaInvestigation of Antarctic deltaic sediments is being undertaken together with Professor D. Sugden (Edinburgh University), and Dr. M. Bentley (Durham University) with support from NERC.