Landscape evolution of the NW Himalayan rivers during the late Quaternary and their non-contemporaneity to the Harappan Civilization

A large perennial river system, the Ghaggar-Hakra, fed by the palaeo-Sutlej and palaeo-Yamuna Rivers from the west and east respectively, has been argued to have sustained the Bronze Age Harappan urban settlements (∼4.6–3.9 ka BP) in NW Himalayan foreland in India and Pakistan. However, it has been demonstrated by previous workers that palaeo-Sutlej was already defunct in this region by ∼8 ka, much before the peak of urbanism. In contrast, the evolutionary history of palaeo-Yamuna, a major feeder to the Ghaggar-Hakra River system, remains weakly documented and enigmatic. This knowledge gap limits our understanding of the influence of regional-scale hydrological conditions on the growth and eventual demise of the Harappan Civilization. Here, we present the high-resolution chronostratigraphic records based on 47 optically stimulated luminescence (OSL) ages from 6 cores (∼50 m deep) retrieved across the palaeochannels of the Yamuna. We document multi-storied sand bodies deposited by a mobile channel belt in a large alluvial fan system characterized by four possible stages of drainage reorganization and landscape evolution during the late Quaternary. It has also been inferred that a major eastward shift of the palaeo-Yamuna River occurred at ∼18 ka, predating both the westward shift of the Sutlej at ∼8 ka and the decline of the Harappan Civilization at ∼3.9 ka BP. Our chronostratigraphic data helps to understand the drainage reorganization of the Himalayan river systems during the late Quaternary in the NW Himalayan foreland and reaffirms the non-contemporaneity of the Harappan Civilization with a large river system.