Abstract
Recent developments in luminescence dating offer new ways to date exposure and burial durations of rocks. The new rock surface dating methods ideally require high-resolution data, faster sample preparation and measurement times, and field screening methods to select samples with appropriate luminescence characteristics and bleaching histories. Presented here is a demonstration of an EMCCD (electron multiplying charge coupled device) based system capable of imaging high-resolution infrared stimulated luminescence (IRSL) and infrared-photoluminescence (IRPL) from rock samples. The IRPL can be detected at both 880 nm and 955 nm. Using this instrument, the entire luminescence-depth profile can be reconstructed by imaging a single surface cut perpendicular to the exposed rock face. We demonstrate the possibility of reconstructing luminescence-depth profiles suitable for rock surface dating from large (cm-scale) rock samples, without using a regeneration dose for normalisation of the natural luminescence signals. Based on the different bleaching characteristics of the IRSL and IRPL emissions at 880 nm and 955 nm, we show that it is possible to gain reliable estimates of bleaching depths from measurement of as few as two images of the IRPL signal (one for each emission), or from measurement of the IRSL decay curve. We thus by-pass laborious sample preparations and the need for a gamma source to estimate the bleaching depth, thereby extending the 2D luminescence-depth profile imaging technique to other laboratories that lack access to ionising radiation facilities. This study also makes a significant progression towards development of a field instrument for in situ relative exposure dating, and sample screening for rock surface burial dating. • Direct imaging of luminescence-depth profiles in rocks using IRPL or IRSL. • New methods for normalising spatial variations in luminescence without irradiation. • Characterising bleachability of different OSL emissions from the principal trap. • Rock surface dating for rapid field analysis or laboratories lacking irradiation facilities.
Highlights
Building chronologies of past geological and archaeological events often requires a range of methods applicable to different types of de posits and materials over different age ranges
We demonstrate the possibility of reconstructing luminescence-depth profiles suitable for rock surface dating from large rock samples, without using a regeneration dose for normalisation of the natural luminescence signals
We demonstrate that it is possible to assess infrared stimulated luminescence (IRSL) and IRPL bleaching depths in rocks using as little as two images, or from the IRSL decay curve alone, obtaining comparable information to profiles normalised with a regeneration dose
Summary
Building chronologies of past geological and archaeological events often requires a range of methods applicable to different types of de posits and materials over different age ranges One such newly devel oped method is optically stimulated luminescence (OSL) dating of exposed or buried rock surfaces. The resulting luminescence-depth profile can be exploited for estimating exposure durations or erosion rates on timescales of up to 105 years (Guralnik and Sohbati, 2019; Lehmann et al, 2018; Sohbati et al, 2012b, 2018) This method of Rock Surface Exposure Dating (RSED) relies on finding a suitable calibration sample with known exposure time. We can establish whether the derived luminescence age from the slices at a particular depth dates the burial event
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