DescriptionI gave this expenses paid invited talk:
Establishing the timing of sediment deposition allows us to constrain the extent of, rate of, and variation within, environmental processes that are driven by changes within the global, regional and local climate. This provides a window on environmental change. Since its development in the mid-1980s, optically stimulated luminescence (OSL) dating has been widely applied as a method to establish the burial age (or age of last exposure to sunlight) of sediments in a wide range of depositional settings. However, full laboratory OSL dating protocols are time consuming, technically demanding and relatively expensive (commercial prices per sample start at ~£550 + tax). For this reason, an increasing level of effort in the luminescence community is being spent on developing approaches to provide a rapid, assessment of sediment age. As a minimum these rapid age estimates may: (i) provide useful relative age control within exposures and augured sequences, or (i) produce range-finder estimates to guide a tighter focused laboratory protocol based dating strategy. At best there is the tantalizing possibility to obtain usable ages from these approaches.
Approaches to rapid OSL age assessment fall broadly into: (1) those that reduce sample preparation time and (2) those which reduce sample measurement time. The references to these are too numerous to list in this abstract – for more details see the brief review provided in Stone et al. (2015). On the side of reducing time spent on preparing samples, luminescence profiling has been undertaking using bulk material (material as extracted during field sampling) to obtain information about sample brightness and relative age, whilst greatly reduced pre-treatments (e.g. not isolating specific grain fractions or chemically isolating the quartz mineral) have been employed to provide rapid initial age estimates. The second set of approaches uses fully prepared samples (refined to quartz, feldspar, or polyminerals) and with a training set of samples measured using luminescence readers in the laboratory produces a standardized growth curve, rather than a growth curve for every sample. This means that subsequent samples only require a very short measurement protocol (2 steps as opposed to in excess of 14), and the values from these are interpolated onto the standardized growth curve to provide an estimate of their
A portable luminescence reader (Figure 1) combines these two approaches by measuring bulk sediment material in luminescence unit (greatly simplified compared to laboratory luminescence readers, and easy to transport) using 60 second stimulation times (with infra-red and then blue diodes). Unlike full laboratory luminescence readers there is no radiation source (to irradiate the sample), or heater plate to preform measurements at elevated temperature.
In this talk, I will outline the use of a potable luminescence reader built by SUERC (Scottish Universities Environmental Research Centre) (Sanderson and Murphy, 2010) within a variety of contexts to understand the processes and timing of global change. We will consider published examples how the reader has been used to identify tsunami deposits in Thailand and the location of ditch fills with host sediment in archaeological applications.
I will also outline ‘calibration’ of the portable reader signals against full luminescence protocol ages for sand samples in the Namib Sand Sea (published in Stone et al., 2015), dunefields and lake shorelines in the Kalahari and dunes in Sweden. A simple linear regression between the blue stimulated signal from the portable luminescence reader and full SAR-protocol OSL burial ages has been produced for the Namib Sand Sea dataset with samples that span 50 to 132,000 years old (Stone et al., 2015) and a Kalahari dataset spanning 500 to 145,000 years. This calibration approach provides a tool to use alongside the portable luminescence reader to make rapid preliminary age assessments of new samples at undated sites out in the field. There is a strong indication that this requires a region-specific approach.
|8 Jun 2017
|Topical Day - Luminescence dosimetry for environment, health and safety
|Degree of Recognition