Investigating the relative timing of the introduction of allochthonous silt in postglacial eolian dunes of central Alberta, Canada using a portable OSL reader

The porous nature of eolian dune sediments enables post-depositional silt and clay to be added to the dune profile with an open-ended timeline. The allochthonous silt results in depositional age-heterogeneity between sand and silt which could encumber investigations that employ portable optically stimulated luminescence (OSL) readers to construct luminescence profiles using unprocessed bulk samples. To establish an approach for ascertaining the relative timing of the introduction of silt, this study used a portable OSL reader to assess the level of allochthonous silt in the upper parts of ca. 15 ka old postglacial eolian dunes in central Alberta, Canada. Four dune profiles were sampled using an auger at 10 cm intervals to a depth of 300 cm. Each sample was sieved into sand and silt with clay fractions (>0.063 mm and <0.063 mm) and then measured with IRSL and post-IR blue OSL using a portable OSL reader. Signals of the bulk samples were also measured for comparison. Results showed that the difference in signal intensity between the bulk samples, sand, and silt with clay fractions was insignificant, suggesting no substantial allochthonous silt was introduced into the area during the Holocene. An alternative source for the silt could be in-situ frost weathering of quartz sand in dune sediment as confirmed by grain surface microtextures from scanning electron microscopy.