Late quaternary fluvial incision and aggradation in the Lesser Himalaya, India

Anthony Dosseto*, Jan-Hendrik May, Jeong-Heon Choi, Zachary J. Swander, David Fink, Oliver Korup, Paul Hesse, Tejpal Singh, Charles Mifsud, Pradeep Srivastava

*Corresponding author for this work

    Research output: Contribution to journalArticle

    5 Citations (Scopus)

    Abstract

    Reconstructing how rivers respond to changes in runoff or sediment supply by incising or aggrading has been pivotal in gauging the role of the Indian Summer Monsoon (ISM) as a geomorphic driver in the Himalayas. Here we present new chronological data for fluvial aggradation and incision from the Donga alluvial fan and the upper Alaknanda River, as well as a compilation of previous work. In addition to conventional OSL-SAR (Single-Aliquot Regenerative-Dose) dating method, we have tested and applied pulsed OSL (POSL) dating for quartz samples that include K-rich feldspar inclusions, which is expected to improve the applicability and validity of OSL ages in the Lesser Himalaya. For previously dated deposits, our OSL ages are shown to be systematically older than previously reported ages. These results suggest periods of aggradation in the Alaknanda and Dehradun Valleys mainly between ∼25 and 35 ka. This most likely reflects decreased stream power during periods of weakened monsoon. In addition, in-situ cosmogenic beryllium-10 was used to infer bedrock surface exposure ages, which are interpreted as episodes of active fluvial erosion. Resulting exposure ages span from 3 to 6 ka, suggesting that strath terraces were exposed relatively recently, and incision was dominant through most of the Holocene. In combination, our results support precipitation-driven fluvial dynamics, which regulates the balance between stream power and sediment supply. On a larger spatial scale, however, fluvial dynamics are probably not spatially homogeneous as aggradation could have been taking place in adjacent catchments while incision dominated in the study area.

    Original languageEnglish
    Pages (from-to)112-128
    Number of pages17
    JournalQuaternary Science Reviews
    Volume197
    DOIs
    Publication statusPublished - 1 Oct 2018

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