Quantifying denudation rates and sediment storage on the eastern Altiplano, Bolivia, using cosmogenic 10Be, 26Al, and in situ 14C

Abstract

Denudation processes and sediment transfer are investigated in a high-elevation, low-relief environment (eastern Altiplano, Bolivia) using 10Be, 26Al, and in situ 14C analysis in fluvial sediments. Concentrations of the long-lived nuclides 10Be and 26Al yield consistently low catchment-wide denudation rates of ~3–29mmky−1 (integrating over 21–194ky), which reflect the low geomorphic gradients and the discontinuity of fluvial transport along the eastern Altiplano margin. No significant correlation is recorded between denudation rates of individual catchments and morphological basin parameters (slope, area, elevation). This is attributed to the overall little variability in morphology. The agreement between the denudation rates and published modern sediment discharge data suggests steady landscape evolution of the eastern Altiplano from the latest Pleistocene until today. While 10Be and 26Al provide long-term estimates on sediment production, in situ cosmogenic 14C is used to trace short-term sediment storage. In situ 14C concentrations are comparatively low indicating that 14C decayed during alluvial storage over at least the past ~11–20ky. We assume storage at shallow depth (2m) and consider the influence of soil-mantled hillslopes on the in situ 14C concentration. Our results illustrate the importance of sediment storage even over short distances and demonstrate the potential of in situ 14C to study sediment routing and transfer times within drainage systems. However, this study also demonstrates that the long-lived 10Be and 26Al nuclides can provide adequate estimates on long-term denudation rates even if sediment transport is not fast but interrupted by several thousands of years of storage.