Late Quaternary tectonic landforms and fluvial aggradation in the Saryu River valley: Central Kumaun Himalaya

Abstract

The present study has been carried out with special emphasis on the aggradational landforms to explain the spatial and temporal variability in phases of aggradation/incision in response to tectonic activity during the late Quaternary in the Saryu River valley in central Kumaun Himalaya. The valley has preserved cut-and-fill terraces with thick alluvial cover, debris flow terraces, and bedrock strath terraces that provide signatures of tectonic activity and climate. Morphostratigraphy of the terraces reveals that the oldest landforms preserved south of the Main Central Thrust, the fluvial modified debris flow terraces, were developed between 30 and 45ka. The major phase of valley fill is dated between 14 and 22ka. The youngest phase of aggradation is dated at early and mid-Holocene (9–3ka). Following this, several phases of accelerated incision/erosion owing to an increase in uplift rate occurred, as evident from the strath terraces. Seven major phases of bedrock incision/uplift have been estimated during 44ka (3.34mm/year), 35ka (1.84mm/year), 15ka (0.91mm/year), 14ka (0.83mm/year), 9ka (1.75mm/year), 7ka (5.38mm/year), and around 3ka (4.4mm/year) from the strath terraces near major thrusts. We postulate that between 9 and 3ka the terrain witnessed relatively enhanced surface uplift (2–5mm/year).