Climate-driven sediment aggradation and incision since the late Pleistocene in the NW Himalaya, India

Abstract

Deciphering the response of sediment routing systems to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution. In the Kangra Basin (northwest Sub-Himalaya, India), upper Pleistocene to Holocene alluvial fills and fluvial terraces record periodic fluctuations of sediment supply and transport capacity on timescales of 103 to 105 yr. To evaluate the potential influence of climate change on these fluctuations, we compare the timing of aggradation and incision phases recorded within remnant alluvial fans and terraces with climate archives.New surface-exposure dating of six terrace levels with in-situ cosmogenic 10Be indicates the onset of incision phases. Two terrace surfaces from the highest level (T1) sculpted into the oldest preserved alluvial fan (AF1) date back to 53.4±3.2 ka and 43.0±2.7 ka (1σ). T2 surfaces sculpted into the remnants of AF1 have exposure ages of 18.6±1.2 ka and 15.3±0.9 ka, while terraces sculpted into the upper Pleistocene–Holocene fan (AF2) provide ages of 9.3±0.4 ka (T3), 7.1±0.4 ka (T4), 5.2±0.4 ka (T5) and 3.6±0.2 ka (T6). Together with previously published OSL ages yielding the timing of aggradation, we find a correlation between variations in sediment transport with oxygen-isotope records from regions affected by the Indian Summer Monsoon. During periods of increased monsoon intensity and post-Last Glacial Maximum glacial retreat, aggradation occurred in the Kangra Basin, likely due to high sediment flux, whereas periods of weakened monsoon intensity or lower sediment supply coincide with incision.