Luminescence profiling of postglacial eolian dunes in central and northern Alberta using a portable OSL reader

Abstract

Regular luminescence dating is a lengthy procedure that entails elaborate sample preparation as well as multiple measurements to arrive at an age of a given sample. In practice, not all samples that may appear datable in the field actually yield useful information in the lab. Consequently, because sample luminescence measurement is only carried out near the end of the dating procedure, a significant amount of time and resources could be expended on samples that ultimately produce no useful data. A technique that can be used to discriminate between samples that could potentially yield useful information and those that would not is luminescence profiling (Bishop et al., 2006; Burbidge et al., 2007; Sanderson and Murphy, 2010). Luminescence profiling does not necessarily provide an absolute age. Instead, it enables one to construct a profile that shows a variation of the luminescence signal with depth. The luminescence signal is dependent on variables such as the burial age and luminescence sensitivity of the sediment, as well as the local dose rates and level of bleaching experienced prior to burial. Where the burial age is the main variable, the luminescence profile could be seen as a proxy for the chronostratigraphy and it enables one to identify changes such as significant age differences between successive strata within a given section, or age variations across erosional contacts. Luminescence profiling measurements can be carried out rapidly in the lab or in the field using a portable OSL reader. Analysis can be done on bulk samples, negating the need to perform time consuming mineralogical separations. In this study, a portable OSL reader is employed to construct luminescence profiles of postglacial eolian dunes from selected sites in central and northern Alberta. In places, the dunes are underlain by glaciofluvial sands but it is often difficult to distinguish between the eolian deposits and the glaciofluvial sediments based on their physical appearances alone. Results from the study show that luminescence profiling can differentiate between the two types of deposits because of differences in their depositional ages and this enables the demarcation of the bases of the dunes. The identification of the dune bottom permits appropriately targeted sample collection for regular luminescence dating in order to constrain the timing of the initiation of eolian deposition in the region. Luminescence profiling is also used in this study to identify depositional breaks of extended duration within the eolian sequences.

Session: Quaternary Paleoenvironments