Reconstruction of landscape change of Shyok valley, Ladakh during Late Quaternary using OSL technique

Abstract

The Shyok Valley, within the Upper Indus Basin in Trans-Himalayas, lies in the cold and arid region. It is fed by the Siachen glacier; the largest glacier in the third pole. The fluctuations in this glacier are attributed to varying intensities of the two weather regimes namely mid-latitude westerlies and Southwest Monsoon. The reconstruction of the magnitude, timing, and landscape impact of glaciers in Nubra-Shyok valley have been explored in past decade yet they are contentious and uncertain. Therefore, the present study investigates the sediments from the key sites (Agham, Khardung, Changmar, Chalunka) in the Shyok valley using Optically Stimulated Luminescence (OSL) dating technique. The diverse geomorphology, including moraines, sand dunes, mass movement zone, alluvial fans are mapped to represent the geomorphic setting of the region. The chronological ages from the lower Shyok Valley (Agham section: 18.4 ± 2.2 ka) suggest extensive glacier expansion beyond the present terminus of the Siachen Glacier during the Marine Isotopic Stage (MIS)-2. The Khardung section has glaciofluvial deposits: 24.0 ± 2.4 ka (KHG-1), younger moraine: 8.2 ± 1.0 ka (KHG-9) and lacustrine deposits (KHGL-5, KHGL-6, KHGL-7): 14.1 ± 2.0 ka, 12.1 ± 1.1 ka, 10.7 ± 1.3 ka. The glacial events that occurred around 8.2 ka and 12.0 ka suggest glacial advancement which are likely due to a period of lower temperature. The Changmar section displays lacustrine deposits and debris flow events dated to the late glacial (14.5 ± 1.7 ka, CHG-1; 13.2 ± 1.6 ka, CHG-2) and deglaciation period (6.5 ± 1.2 ka, CHG-3; 5.5 ± 1.0 ka, CHG-4). The presence of the Holocene-aged lateral moraines (20 km away from Chalunka village: 14.3 ± 1.3 ka, CLM-2; 5.7 ± 0.9 ka, CLM-3; 0.4 ± 0.04 ka, CLM-4) and CHG-8: 2.1 ± 0.3 ka; outwash plain deposits: COP-7: 2.4 ± 0.4 ka aligns with the previous findings in the Nubra Valley, suggesting glacial advance in Little Ice Age in the whole valley. The glacial event occurring between 2.4 and 2.1 ka corresponds to the Neoglacial epoch, characterized by a glacial advance likely caused by a decrease in temperature during the late Holocene period. The intensified mid-latitude westerlies during MIS-2 are inferred to be the key factor in increased moisture to the Shyok Valley which led to the glacier expansion. These findings enhance our understanding of past climate changes in this high-altitude region and serve as a valuable baseline for future studies on glacial response to climate variations.