Single-grain and single-aliquot luminescence measurements of partially bleached modern-river channel sediments: applications to sediment transport

Abstract:

Luminescence techniques are an emerging tool to track transport and provenance of grains in Quaternary fluvial and aeolian deposits. The incomplete zeroing of luminescence signals (partial bleaching) in fluvial environments is an obstacle for dating, but proves advantageous for extracting information about grain-transport histories. Luminescence signals from quartz and feldspar sand have been observed to decrease as an exponential or stretched exponential function of distance downriver. A theoretical framework for the reduction in signal of quartz grains in ephemeral rivers has recently been proposed. We present improvements to a simple forward model for reduction in signal observed for small-aliquot multiple elevated temperature post-IR infrared stimulated luminescence (MET-pIRIR) of K-feldspar grains on the Mojave River in Southern California. Specifically, we use USGS historical stream gage records to produce synthetic hydrographs using time-series analysis. The synthetic hydrographs are used as inputs for an iterative model of signal growth (burial period between floods) and signal depletion (light exposure period during floods). From a best fit of this model to small-aliquot MET-pIRIR data, we can estimate virtual velocity of fine-grain (175 – 200 µm) sand from source to sink. Additionally, we present single-grain MET-pIRIR measurements of K-feldspar grains from the Mojave River and the Santa Clara River in Southern California and explore applications of single-grain data to provenance studies.