Fluvial response to climate change inferred from sediment cores from the Ghaggar–Hakra paleochannel in NW Indo–Gangetic plains

In the Indo–Gangetic plains (IGP), the inter–basinal area between the Ganga in east and the Indus in west is currently devoid of any major drainage. A wide paleochannel belt, the Ghaggar-Hakra channel, has been mapped in this region. Our previous studies along with others established that a large Himalayan river flowed through this paleochannel, and a large–scale drainage reorganisation occurred during the last 10 ka. This follow-up study presents sedimentary facies and chrono–stratigraphy of the alluvial deposits from the Ghaggar-Hakra paleochannel (1) to understand the depositional environments of the river system; (2) to reconstruct aggradation/incision history and stratigraphic development, and (3) to understand fluvial response to climate change at a regional scale. Sediment cores (35–50 m) across the length and width of the paleochannel, and optically stimulated luminescence (OSL) based chronology are used to reconstruct alluvial stratigraphy developed during marine isotope stage (MIS) 5-1. Twelve sedimentary facies identified in the cores characterize floodplain, channel, and aeolian depositional settings. Four stratigraphic units were identified; the oldest Unit 1 (>150 ka) representing aeolian deposition disconformably underlies the younger Units 2 to 4 that represent four periods of fluvial aggradation (and incision). Period I (~86–64 ka) comprises coarse grained grey micaceous channel sand, and period II (~62–30 ka) shows transition to fine to medium channel sand interlayered with yellow mud of floodplain deposition. Period III (~25–12 ka) comprised of fine grained grey micaceous channel sand and very fine deposits of channel margin settings. Period IV (~11–4.0 ka) marks the termination of flow from the large Himalayan river, the Sutlej, into the Ghaggar-Hakra system and fluvial sequence in this period, red brown silty clay, represents modern Ghaggar deposits. We suggest a strong climatic control on the stratigraphic development in this region based on the available proxy records. We further compare our stratigraphic data with that of the IGP and the adjoining western Indian rivers for understanding the regional-scale fluvial response to monsoonal fluctuations.by Ajit Singh and Rajiv Sinh