Articles | Volume 3, issue 1
Earth Surf. Dynam., 3, 55–65, 2015
Earth Surf. Dynam., 3, 55–65, 2015

Research article 16 Jan 2015

Research article | 16 Jan 2015

Re-evaluating luminescence burial doses and bleaching of fluvial deposits using Bayesian computational statistics

A. C. Cunningham1,2, J. Wallinga3, N. Hobo3,4,5, A. J. Versendaal3, B. Makaske3,4, and H. Middelkoop5 A. C. Cunningham et al.
  • 1School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
  • 2Centre for Archaeological Science, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, Australia
  • 3Soil Geography and Landscape group & Netherlands Centre for Luminescence dating, Wageningen University, Wageningen, the Netherlands
  • 4Alterra, Wageningen University and Research Centre, Wageningen, the Netherlands
  • 5Department of Physical Geography, Utrecht University, Utrecht, the Netherlands

Abstract. The optically stimulated luminescence (OSL) signal from fluvial sediment often contains a remnant from the previous deposition cycle, leading to a partially bleached equivalent-dose distribution. Although identification of the burial dose is of primary concern, the degree of bleaching could potentially provide insights into sediment transport processes. However, comparison of bleaching between samples is complicated by sample-to-sample variation in aliquot size and luminescence sensitivity. Here we begin development of an age model to account for these effects. With measurement data from multi-grain aliquots, we use Bayesian computational statistics to estimate the burial dose and bleaching parameters of the single-grain dose distribution. We apply the model to 46 samples taken from fluvial sediment of Rhine branches in the Netherlands, and compare the results with environmental predictor variables (depositional environment, texture, sample depth, depth relative to mean water level, dose rate). Although obvious correlations with predictor variables are absent, there is some suggestion that the best-bleached samples are found close to the modern mean water level, and that the extent of bleaching has changed over the recent past. We hypothesise that sediment deposited near the transition of channel to overbank deposits receives the most sunlight exposure, due to local reworking after deposition. However, nearly all samples are inferred to have at least some well-bleached grains, suggesting that bleaching also occurs during fluvial transport.

Short summary
Rivers transport sediment from mountains to coast, but on the way sediment is trapped and re-eroded multiple times. We looked at Rhine river sediments to see if they preserve evidence of how geomorphic variables have changed over time. We found that measured signals potentially relate to water level and river management practices. These relationships can be treated as hypotheses to guide further research, and our statistical approach will increase the utility of research in this field.