Seminar by Louise Karman-Besson (LPG) – « Potential of feldspars single-grain luminescence to reveal sediment input and transport in fluvial systems »

Fluvial systems play a major role in shaping landscapes and transferring sediment from source areas to depositional sinks. This transfer is, however, highly discontinuous, involving repeated phases of mobilisation, transport, deposition, and temporary storage, particularly within alluvial plains. These processes control sediment transit times and modulate the transmission of environmental signals, such as those associated with climatic and tectonic forcing. Understanding and quantifying these dynamics is therefore essential for characterising the propagation of sedimentary signals through fluvial and source-to-sink systems.

By exploring the potential of feldspar luminescence as a tracer of sediment transport history, these studies investigate the interactions between sediment supply, transport, storage, and bleaching in fluvial systems. The progressive resetting of the luminescence signal through light exposure during transport provides constraints on grain transport histories and allows the balance between signal attenuation by bleaching and its renewal through the input of poorly bleached sediment to be investigated. Field datasets from New Zealand and Chile are combined with stochastic modelling of sediment transport and storage to identify the processes controlling downstream luminescence patterns.

The results show that downstream variations in luminescence cannot be explained simply by transport distance or environmental gradients alone. Instead, they reflect the interaction between bleaching efficiency, which progressively reduces the signal, and the input of less-bleached material, which can maintain or increase the luminescence of the sediment flux. The relative importance of these processes depends on geomorphic context, the spatial distribution of sediment sources, and hydrological variability, producing a continuum of behaviours from progressive downstream signal decay to signal stabilisation or increase. The study of an exceptional flood in Chile in 2023 further shows that luminescence can detect the mobilisation of new sediment sources and track their downstream propagation, while also revealing the potential persistence of signatures inherited from earlier phases of sediment production and transfer. Luminescence could therefore provide means of linking event-scale sediment dynamics with the longer-term evolution of landscapes.