Linking single-grain luminescence and erosion rates to understand erosional and sediment dynamics in the Southern Central Andes, Chile

Hillslope processes play a significant role in shaping catchment-scale erosional dynamics. These processes include mechanisms from granular creep to large-scale morphological changes influenced by tectonic and climatic forces over both short and long timescales. Despite advancements in quantification methods, a granular-level understanding of these processes remains unclear. Moreover, a systematic approach to link the variability of hillslope processes across different temporal scales is still lacking. Thus, integrating single-grain luminescence analysis with cosmogenic nuclide-derived erosion rates from modern fluvial deposits can bridge these gaps, offering deeper insights into hillslope processes.

Single-grain luminescence provides detailed grain-specific insights into sediment production, erosion, transport, and deposition processes over millennial timescales. In contrast, cosmogenic nuclide-based methods analyze the long-term mean signal from a large grain population. Thus, comparing single-grain luminescence dose distribution with cosmogenic ¹⁰Be-derived catchment-wide erosion rates in fluvial sediments could help identify various hillslope processes with higher analytical resolution over varying timescales. We hypothesized that grains transported by soil creep will be sufficiently bleached (zero or negligible remaining luminescence signal). In contrast, grains transported via landslides will predominantly exhibit incomplete or no bleaching (considerable remaining luminescence signal or saturated with luminescence signal).

To test this hypothesis, we measured the proportion of bleached versus non-bleached grains in modern fluvial deposits sourced from 11 catchments falling in a climatic gradient and also with contrasting morphometric properties in the Southern Central Andes (Chile) using post-IR IRSL signal of K-feldspar. Contrary to expectations, we observed a weak negative correlation between the proportion of bleached grains and erosion rates, suggesting complex transport dynamics and variable opportunities for bleaching across catchments. Additionally, a weak positive correlation between non-bleached grains and erosion rates suggests complex sediment storage and reworking within the system, and an absence of large morphologic changes, such as deep-seated landslides.

Therefore, comparing the luminescence signals of hundreds of grains with catchment-wide erosion rates across various temporal scales provides valuable complementary insights into (a) the mechanisms driving hillslope erosion, (b) their influence on catchment-wide erosion rate estimates, and (c) the complex sediment dynamics within catchments.