Glacial influence on late Pleistocene 10Be-derived paleo-erosion rates in the north-western Himalaya, India
Glacial influence on late Pleistocene 10Be-derived paleo-erosion rates in the north-western Himalaya, India
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DOI：
10.1016/j.epsl.2020.116441
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发表时间：
2020-10
影响因子：
5.3
通讯作者：
René Kapannusch;D. Scherler;G. King;H. Wittmann
中科院分区：
文献类型：
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作者：
René Kapannusch;D. Scherler;G. King;H. Wittmann
河流沉积物中的陆地宇宙成因核素浓度可用于估算古侵蚀速率和重建地貌对气候扰动的反应。然而，在部分被冰覆盖的景观中，掺入被冰与宇宙屏蔽的冰下沉积物可能会导致错误的侵蚀率计算。在这里，我们结合在situ-produced 10 Be衍生的侵蚀速率，基于砂和卵石从河流填充阶地和现代河床在亚穆纳河上游流域，数值冰流模型来量化这种偏见。新的释光年龄和地表暴露年龄表明，暴露沉积物的沉积时间为29.9 ± 2.5 ~ 14.8 ± 2.8ka。在大部分的沉积过程中，冰川可能覆盖了1019%的集水区。10 Be浓度的阶地砂样品不同的卵石样品。我们得到了最低的侵蚀率从石英岩卵石，这是干从低海拔，和最高的侵蚀率从结晶卵石，这是干从高海拔的亚穆纳流域。我们解释这些不同的侵蚀速率的差异，陡峭的源区，在整个加积期，尽管显着的前冰盖的影响，普遍存在。砂样，这被认为是来自所有海拔部分的集水区，然而，显示lower 10 Be浓度在加积相比，今天。我们认为，这种差异是由于大量的冰下起源的砂在加积期，并不一定与增强侵蚀。我们的结论是，在亚穆纳集水区的山谷填充的加积是最有可能的，由于减少排放，只有轻微的相关，在晚更新世的侵蚀率较高。
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 combinein situ-produced10Be-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 lower10Be 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.