Recycling of Pleistocene valley fills dominates 135 ka of sediment flux, upper Indus River

Abstract

Rivers draining the semiarid Transhimalayan Ranges at the western Tibetan Plateau margin underwent alternating phases of massive valley infill and incision in Pleistocene times. The effects of these cut-and-fill cycles on millennial sediment fluxes have remained largely elusive. We investigate the timing and geomorphic consequences of headward incision of the Zanskar River, a tributary to the Indus, which taps the >250-m thick More Plains valley fill that currently plugs the endorheic high-altitude basins of Tso Kar and Tso Moriri. In situ 10Be exposure dating and topographic analyses show that a phase of valley infill gave way to net dissection and the NW Himalaya's first directly dated stream capture in late Marine Isotope Stage (MIS) 6, ∼135 ka ago. Headwaters of the Indus are currently capturing headwaters of the Sutlej, and rivers have eroded >14.7 km3 of sediment from the Zanskar headwaters since, mobilising an equivalent of ∼8% of the Indus' contemporary sediment storage volume from only 0.3% of its catchment area. The resulting specific sediment yields are among the rarely available rates averaged over the 105-yr timescale, and surpass 10Be-derived denudation rates from neighbouring catchments three-to tenfold. We conclude that recycling of Pleistocene valley fills has fed Transhimalayan headwaters with more sediment than liberated by catchment denudation, at least since the last glacial cycle began. This protracted release of sediment from thick Pleistocene valley fills might bias estimates of current sediment loads and long-term catchment denudation. Disciplines Medicine and Health Sciences | Social and Behavioral Sciences

Climatic and glacial impact on erosion patterns and sediment provenance in the Himalayan rain shadow, Zanskar River, NW India

“…The abundance of quartzofeldspathic, micaceous, and schistose metamorphiclastic detritus in the Zara (ID #10) sample might suggest an overspill connection existed between Tso Kar and the Zanskar River, as proposed by Demske et al (2009) andWünnemann et al (2010). Our provenance data from the Zara River neither support nor preclude sediment supply to the Zanskar River via an overspill connection (e.g,, Munack et al, 2016).…”

“…Significant dissection of Pleistocene valley-fills in the upper Tsarap catchment highlights a long history of sediment reworking into the paleo-Zanskar River (Munack et al, 2016).…”

Millennial and centennial variations in zircon U‐Pb ages in the quaternary indus submarine canyon

“…There are multiple opportunities for sediment buffering in the Indus basin, especially because the flood plains are long (>1,000 km; Figures 1 and 2). Sediment storage in mountain terraces is also well documented (Blöthe et al, 2014;Jonell, Owen, Carter, Schwenniger, & Clift, 2017;Munack et al, 2016), and a high fraction of the Holocene sediment supply appears to be derived by reworking from these terraces , as well as large-scale incision of the flood plains . Furthermore, the Indus River recycles sediment from the neighbouring Thar Desert (Figure 2), which itself is supplied by aeolian sediment transport from the delta, especially during interglacial times when the summer monsoon winds are powerful (East, Clift, Carter, Alizai, & VanLaningham, 2015).…”

Quantifying episodic erosion and transient storage on the western margin of the Tibetan Plateau, upper Indus River

“…Across the Himalaya, wide (>5 km), glacially scoured, and overdeepened intermontane river basins provide exceptional accommodation space for sediment storage (Owen et al, 2006; Korup et al, 2010; Bolch et al, 2012; Blöthe and Korup, 2013). Thick alluvial river terrace sequences document considerable storage and release of sediment on shorter, climate-relevant time scales (Bookhagen et al, 2006; Srivastava et al, 2008; Blöthe et al, 2014; Scherler et al, 2015; Dey et al, 2016; Munack et al, 2016).…”