Developing a new approach to the luminescence dating of sediments from glacial contexts

Abstract

Whether glacial sediments were exposed to light (bleached) prior to burial is uncertain but critical for luminescence dating. In such contexts, quartz can have unstable and weak signals, feldspar have less bleachable and fading signals and both require statistical modelling to extract the true burial age data. This paper presents a new approach using feldspars measured at multiple elevated temperatures (MET) and screened to select grains with plateau equivalent dose values which should be the well-bleached and unfaded grains upon which to base a true burial age. The MET plateau approach was tested on an aeolian site in Canada and two former UK glacial sites. When applied to the Canadian aeolian samples, it showed that the method successfully accepted mostly well-bleached grains whilst excluding grains with fading or that had poor luminescence characteristics. When applied to a well dated glacial sequence it yielded ages in good agreement with existing independent chronologies. A previously undated glacial site yielded stratigraphically consistent ages but these are thought likely to be slight age over-estimates due to extremely limited bleaching at deposition. In summary, the MET plateau approach improved avoidance of partially bleached grains, avoided corrections for residuals and/or fading and reduced the need for statistical models to interpret equivalent dose distributions. However, some glacial sediments may have had so limited bleaching that these may still not be easy to luminescence date. The MET plateau approach if adopted could allow re-evaluation of existing glacial chronologies and extend luminescence dating to more glacial sediments.