Abstract

Terrestrial cosmogenic nuclide concentrations in sediment are used to quantify mean denudation rates in catchments. This article explores the differences between the Be-10 concentration in fine (sand) and in coarse (1-3 or 5-10 cm pebbles) river sediment. Sand and pebbles were sampled at four locations in the Huasco Valley, in the arid Chilean Andes. Sand has Be-10 concentrations between 4.8 and 8.3.10(5) at g(-1), while pebbles have smaller concentrations between 2.2 and 3.3.10(5) at g(-1). It appears that the different concentrations, systematically measured between sand and pebbles, are the result of different denudation rates, linked with the geomorphologic processes that originated them. We propose that the Be-10 concentrations in sand are determined by the mean denudation rate of all of the geomorphologic processes taking place in the catchment, including debris flow processes as well as slower processes such as hill slope diffusion. In contrast, the concentrations in pebbles are probably related to debris flows occurring in steep slopes. The mean denudation rates calculated in the catchment are between 30 and 50 m/Myr, while the denudation rates associated with debris flow are between 59 and 81 m/Myr. These denudation rates are consistent with those calculated using different methods, such as measuring eroded volumes. (C) 2013 Elsevier B.V. All rights reserved.