Statistical treatment of fluvial dose distributions from southern Colorado arroyo deposits

Many of the small-scale arroyo systems found across southern Colorado contain well-preserved sedimentary records of prehistoric fluvial erosion and aggradation epicycles. In the following paper, we date a set of 50 ephemeral fluvial samples from four southern Colorado arroyo systems using a combination of single-grain and single-aliquot OSL techniques. Analysis of the sample De distribution characteristics reveals that these arroyo sediments were subjected to a diverse array of bleaching conditions prior to deposition. The use of appropriate burial dose estimation procedures is therefore deemed vital to ensuring that accurate age estimates are produced for each of these samples. In this study we apply the formal ‘age model’ decision procedures of Bailey and Arnold [Statistical modelling of single-grain quartz De distributions and an assessment of procedures for estimating burial dose. Quaternary Science Reviews, in press.] and Arnold [2006. Optical dating and computer modelling of arroyo epicycles in the American Southwest. D.phil. Thesis, University of Oxford, unpublished] to our fluvial sample dataset in order to enable a more objective selection of appropriate burial dose estimates. The resultant OSL chronostratigraphies are examined and discussed. These formal decision procedures yield sample ages that are stratigraphically consistent for 94% of the 50 fluvial samples examined. The resulting OSL ages also display a greater degree of stratigraphic consistency in comparison to those ages that would have been generated by simply applying a single type of age model to all samples.