Extending capacity for luminescence-based chronology

Lead Research Organisation: University of Oxford
Department Name: Geography - SoGE

Abstract

Without robust age control, reconstructing the past dynamics of the Earth system in response to external forcing is problematic. Chronometry is a critical part of studying past environmenst, climates, ecology, human evolution and human landscape-use. Several excellent methods for dating ancient material exist. In many environmental contexts, however, optically-stimulated luminescence (OSL) dating is the only method than can be used, due to the nature of the sediments that preserve the environmental record. The Oxford laboratory has long-running research excellence in studying the last approximately 100,000 years of Earth's terrestrial history, specifically in African and other dryland regions, including Arabia, India and China. These studies have focused on changes in landscape conditions, including ancient lakes and rivers, and on questions of archaeology and human evolution, including responses to environmental change and mobility. The extent and conviction with which such studies can make conclusions is affected strongly by the quality and range of the chronology available. Having greater confidence in the dates derived from analysed sediments, and being able to extend the age range beyond what is currently possible, would allow a host of new research questions to be addressed that would greatly advance these fields. This includes establishing long (up to 1Ma) terrestrial records of climate change, much needed by both the archaeological and modelling communities, making major contributions to our understanding of both human prehistory, past climate changes and, ultimately improvements to model predictions of future climate change.
Oxford has been a leader in luminescence dating development and applications for over 40 years. The new laboratory equipment, a VLS luminescence reader and complementary MiDose radiation measurement device, will provide state-of-the-art equipment that will enable new technical developments. VLS analysis facilitates investigation of a new method of measurement, allowing different dating signals to be observed, pushing the dating limit back beyond 1 million years of Earth's history - a significant improvement on current capabilities. Over time, the signals 'fill-up' due to exposure of the sampled sediments to natural background radiation. The signals typically used for optical dating fill-up over the course of around 100,000 years - and it is essential for accurate dating to know this 'filing rate'. The signals observable using the VLS equipment may take over 1 million years to fill, therefore extending our dating capabilities significantly beyond the reliable limits of 'traditional' OSL dating, allowing us to learn a great deal more about Earth's history and that of humans on the landscape over this period.
This would represent a step change in OSL applications, creating one of the first UK luminescence labs to date sediments back to >1 million years via the luminescence reader with VLS attachment. MiDose provides the means to measure, in a sophisticated way, the various components of the natural background radiation dose rate of the samples, and therefore to calculate the 'filling rate' with greater confidence. This equipment will allow us to improve determination of both components of a luminescnce age, the accumulated dose and the dose rate. Together, this will provide the opportunity to answer for the first time long-standing environmental and archaeological questions These include, for example, testing climate model outputs with terrestrial evidence for large-scale hydroclimate drivers, and establishing the timing of ancestral human presence in drylands (many importnat ancestral modern human sites are in dryalnd regions), and greatly improving capabilities to reconstruct environmental variability over timescales >100,000 years in environmental contexts where dating methods other than OSL cannot be applied.

Planned Impact

IMPACT
In general terms, the ability to extend the datable age range of optical dating to beyond 1,000,000 years would have significant impacts on many areas of Quaternary science, palaeoanthropology and archaeology. Important terrestrial archives of environmental conditions are currently under-utilized due to poor chronological constraints - loess deposits, evidence of former ice extent from previous glacial cycles, ancient lake sediments from deep basins, and spatially extensive palaeodune archives, for example. For archaeological and palaeoanthropological science, records of early human presence/dispersal, and questions of co-existence of now extinct hominid species will become answerable with the addition of longer-range dating tools. The Oxford laboratory has past and ongoing projects in many such areas, and the addition of the new equipment described will have an impact on these project measurable through future publications, grant applications and expanded collaborative projects.

SOCIAL OR ECONOMIC BENEFITS
The benefit to society of this work is not measured in direct economic terms. The impact on society of a deeper understanding of the natural world, the natural drivers of environmental change, the evolution and eventual dominance of our human species, are easily apparent. Of more immediate and current importance, is a recognition that climate, hydrological and other environmental systems have an unexpectedly broad range of operating conditions - vitally important in present-day concerns over global climate and environmental change. It is partly, and significantly, through a recognition of past conditions that the sensitivity of the present-day Earth system to human-induced perturbations can be recognised. The dating of evidence from the past allows correlation of drivers and responses, regional and global synchrony, and the absolute rates of change to be assessed. As such, this proposed expansion of laboratory capabilities plays an important part in this process.

OUTPUTS, ACTUAL AND POTENTIAL BENEFICIARIES
Guaranteed outputs from this investment in capacity include a significant collection of new dating results, based on both standard OSL methods (single aliquot and single grain) and the novel application of the VLS approach, with an extended time range and enhanced dose rate determinations. Existing databases (e.g. the open access INQUA global dune date database, and the developing new palaeolake data base) will benefit from this expansion in capacity as a core aim of asset use is to publish all ages that result. As such the data produced will be in the public domain. Beyond the individual ages (and the scientific advances that follow), improvements to long-range dating capabilities will have a methodological impact, with potentially far wider impact in the long term. Publications outlining such advances are expected to be highly cited.
Collaborative activities will be impacted significantly through this expansion of capacity. This bestows joint benefits on both the laboratory members and collaborators, but more widely bestows benefits on UK science, both in building region and national capacity and in international standing. This is particularly the case in the present case, given the very wide range of national and international collaborations already underway, and the potential for further collaboration that comes with an expansion of the dating range beyond current constraints.

Publications

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