Using single-grain feldspar luminescence signal and modelling to study landscapes erosion rates and sediment transport

Luminescence is a powerful dating technique that is increasingly being used as a new tool to investigate surface processes. In the past decade, it has been used successfully for instance to estimate virtual sediment velocity in rivers, sediment storage time in floodplains, and to trace sediment sources (McGuire & Rhodes, 2015; Gray et al., 2018; Sawakuchi et al., 2018; Guyez et al., 2022; Guyez et al., 2023). As part of ongoing development, here we quantify sediment transport and catchment-wide erosion rates in natural systems using luminescence. For this purpose, single-grain post infrared-infrared (pIRIR) equivalent doses of felspars from modern floodplain deposits were measured in several catchments in the Southern Alps of New Zealand and compared to catchment-wide erosion rates derived from ¹⁰Be cosmogenic nuclide concentrations measured in fluvial quartz grains.

The fraction of grains that were well-bleached before their burial in the modern floodplain was calculated, as well as the fraction of grains with a saturated luminescence signal. Signal distribution was characterised using the central age model.

Our findings indicate that the luminescence signal is characterized by few well-bleached grains and lots of grains with a high luminescence signal where erosion rates are high. On the other hand, in catchments with lower erosion rates, bleaching appears to be more pervasive, resulting in an overall lower luminescence signal. Therefore, we hypothesize that bleaching efficiency is related to erosion rates.

To test the relationship between luminescence, bleaching, erosion, and transport processes, we include the luminescence signal of individual grains in a landscape evolution model that already takes into account the concentration of cosmogenic nuclides (Carretier et al., 2023). By tracking both signals in an evolving stream basin, the model helps better understanding the relationship between erosion and luminescence signal, on longer time scales. Single-grain pIRIR equivalent holds promise as a new method for measuring erosion and sediment transport.