Impact of glacial erosion on ¹⁰Be concentrations in fluvial sediments of the Marsyandi catchment, central Nepal

Abstract

[1] Several processes contribute to denudation in high-mountain environments. Of these, glacial erosion is particularly difficult to constrain, despite its critical importance in the evolution of many mountain ranges. In this study, we present a new data set of 10 Be concentrations in fluvial sediments sampled along the Marsyandi River and its main tributaries in central Nepal. We interpret the 10 Be concentrations as being significantly impacted by glacially derived sediments along the Marsyandi River. Such additions complicate conventional interpretations of 10 Be-derived catchment-scale denudation rates. Using a simple linear mass-conservation formulation, we invert our data set in order to separate the different denudational contributions to the observed signal, as well as to constrain their magnitude and spatial distribution. Our results suggest significant variations in glacial erosion, both in space and magnitude, within the Marsyandi catchment.Citation:

<sup>10</sup>Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

“…This later estimate lies at the higher end of the previous estimates of denudation in the NBGPm, which range between 5 and 17 mm yr −1 (Stewart et al, 2008;Enkelmann et al, 2011;Larsen and Montgomery, 2012). These denudation rate estimates are also all significantly higher than other 10 Be denudation rates reported for other Himalayan catchments (Vance et al, 2003;Wobus et al, 2005;Finnegan et al, 2008;Lupker et al, 2012;Godard et al, 2012Godard et al, , 2014Puchol et al, 2014;Scherler et al, 2014;Le-Roux-Mallouf et al, 2015;Portenga et al, 2015;Morell et al, 2015;Olen et al, 2015Olen et al, , 2016Abrahami et al, 2016), highlighting the significance of the NBGPm as a denudational hot spot.…”

“…Another possible source of perturbation of TCN signals in high-altitude environments such as the Himalayas is the input of glacial sediments. Glacially sourced sediments have been shielded from cosmic rays due to the thick ice cover and therefore have low 10 Be concentrations (Godard et al, 2012;Delunel et al, 2014). Figure 5 shows the evolution of the drained glaciated area along the main stream of the Tsangpo-Brahmaputra.…”

“…The stochastic nature of sediment supply to the channels and hydrology within the river network may also perturb the TCN signal over a range of timescales and limits our ability to use a single sediment sample as a representative and accurate representative of upstream erosion products (Kober et al, 2012;Lupker et al, 2012;West et al, 2014;Foster and Anderson, 2016). Glacial erosion is not properly accounted for, as sediments eroded under a glacier are shielded from cosmic rays and, hence, supply sediment with very low TCN concentrations independent of glacial erosion rates (Godard et al, 2012;Delunel et al, 2014). Different erosion processes also affect the final grain size of fluvially exported sediment, which may in turn lead to a grain size dependence of TCN signals that needs to be taken into account in order to derive robust CWDRs (Clapp et al, 2002;Belmont et al, 2007;Aguilar et al, 2014;Puchol et al, 2014;Lukens et al, 2016).…”

Tectonic controls of Holocene erosion in a glaciated orogen

“…As a result of Cenozoic climate change, the relationships between topographic metrics and observed Holocene (last ∼ 12 kyr) erosion rates in glaciated mountain ranges are more complex than in purely fluvial settings (Moon et al, 2011;Godard et al, 2012;Glotzbach et al, 2013). These poorly understood relationships are likely caused for two reasons: (1) glaciers reorganized previously fluvial channel networks and relief to create a landscape with their preferred geom-etry, radically changing the orogen topography (Whipple et al, 1999;MacGregor et al, 2000;Brocklehurst and Whipple, 2002, 2004Anderson et al, 2006Adams and Ehlers, 2017), and (2) Holocene erosion rates may be dominated by transient signals as surface processes remove the topographic disequilibrium imposed by glacial erosion (Moon et al, 2011).…”

Tectonic controls of Holocene erosion in a glaciated orogen

“…As a result of Cenozoic climate change, the relationships between topographic metrics and observed Holocene (last ~12 kyr) erosion rates in glaciated mountain ranges are more complex than in purely fluvial settings (Moon et al, 2011;Godard et al, 2012;Glotzbach et al, 2013). These poorly understood relationships are likely caused for two reasons.…”