Investigating post-depositional sediment mixing at an archaeological site on the northern Plains using a portable optically stimulated luminescence (OSL) reader

The Bodo Archaeological locality is a major multicomponent site located in east-central Alberta, Canada, in a fossil aeolian dune landscape. About five decades ago, oilfield-related pipeline construction activity resulted in the post-depositional stratigraphic disturbance of some parts of the site. However, the absence of easily discernible signs of anthropogenic disturbances makes visual identification of the disrupted sequences difficult. As a result, identifying sequences that yield accurate reconstructions of the archaeological occupations is problematic. In an effort to differentiate between areas at the site that are intact from those that have been disturbed, this study employed a portable optically stimulated luminescence reader to construct luminescence profiles that show the variation of luminescence signal intensities with depth. The results show that depositional sequences that have undisrupted stratigraphy display signal intensities that decrease up the sequence, correlable with depositional age. Conversely, areas with disrupted stratigraphy are characterized by signals that fluctuate with depth, which results from mixing of strata of dissimilar age. Luminescence profiling also allows the approximation of relative ages of depositional units and these show that, in the undisturbed sites, sediments at the base of the sequences are about three to four times older than sediments in the upper parts. Overall, the ability to identify stratigraphic sequences that are intact enables investigators to expend time and resources on stratigraphic records that yield accurate archaeological reconstructions.