Abstract Terrestrial cosmogenic nuclide concentrations in fluvial deposits allow estimation of paleo-erosion rates and reconstruction of the response of landscapes to climatic perturbations. In partly ice-covered landscapes, however, incorporation of subglacially-derived sediments that were shielded by ice from cosmic can lead to erroneous erosion rate calculations. Here, we combine in situ-produced 10Be-derived erosion rates, based on sand and pebbles from a fluvial fill terrace and the modern riverbed in the upper Yamuna catchment, with numerical ice flow modelling to quantify this bias. New luminescence and surface exposure ages suggest that aggradation of the exposed deposits occurred between 29.9 ± 2.5 ka and 14.8 ± 2.8 ka. During most of the deposition, glaciers probably covered ∼19% of the catchment. 10Be concentrations of terrace sand samples differ from those of pebble samples. We obtained the lowest erosion rates from quartzite pebbles, which stem from low elevations, and the highest erosion rates from crystalline pebbles, which stem from high elevations in the Yamuna catchment. We explain these different erosion rates by differences in the steepness of the source areas, an effect that prevails throughout the entire aggradation period despite significant former ice-cover. Sand samples, which are thought to be derived from all elevation parts of the catchment, however show lower 10Be concentrations during the aggradation compared to present-day. We argue that this difference is due to a substantial subglacial origin of the sand during the aggradation period, and not necessarily related to enhanced erosion. We conclude that aggradation of the valley fill in the Yamuna catchment is most likely due to reduced discharge, and only marginally related to higher erosion rates during the late Pleistocene.

中文翻译：

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冰川对印度喜马拉雅西北部晚更新世 10Be 衍生的古侵蚀速率的影响

摘要 河流沉积物中的陆地宇宙成因核素浓度允许估计古侵蚀率和重建景观对气候扰动的响应。然而，在部分被冰覆盖的景观中，冰下沉积物的结合可能会导致错误的侵蚀率计算。在这里，我们结合了原位产生的 10Be 衍生的侵蚀率，基于来自河流填充阶地和上游亚穆纳集水区的现代河床的沙子和鹅卵石，以及数值冰流模型来量化这种偏差。新的发光和表面暴露年龄表明暴露沉积物的聚集发生在 29.9 ± 2.5 ka 和 14.8 ± 2.8 ka 之间。在大部分沉积过程中，冰川可能覆盖了约 19% 的集水区。阶地砂样品的 10Be 浓度与卵石样品的浓度不同。我们从低海拔的石英岩卵石中获得了最低的侵蚀率，而从亚穆纳流域高海拔的结晶卵石中获得了最高的侵蚀率。我们通过源区陡峭程度的差异来解释这些不同的侵蚀率，尽管以前有显着的冰盖，但这种影响在整个加成期都普遍存在。沙子样本被认为来自集水区的所有高地部分，但与现在相比，在集聚期间显示出较低的 10Be 浓度。我们认为，这种差异是由于在积聚时期沙子的大量冰下起源，不一定与侵蚀增强有关。