Abstract

Alluvial landscapes built by large perennial rivers form the environmental templates on which the earliest urban societies nucleated. Large-scale spatiotemporal settlement patterns in these societies are postulated to have been influenced by river migration across alluvial floodplains. During the early to mid-third millennium BCE , the Indus Civilisation developed one of the most extensive urban cultures in the Old World. This civilisation was established on the alluvial plains of the Indo-Gangetic basin in northwestern India and Pakistan, with an urban phase commencing _{4.6-4.5 ka B.P. It was contemporaneous with and more extensive in area than the earliest urban societies of Egypt and Mesopotamia, encompassing an area estimated at} 1 million km2. Urbanism here has been linked to water resources provided by large Himalayan river systems, however the largest concentrations of urban-scale Indus settlements are located far from extant Himalayan rivers. Why numerous Indus settlements should have been located in a region now devoid of large perennial rivers has been the subject of vigorous debate and controversy.

In this talk, I present geological data to resolve the long-standing issue of the drainage evolution of rivers on the northwestern Ganges Plains by characterising the nature of late Quaternary fluvial deposition, up to and including the time of Indus Civilisation urbanisation. Using optically-stimulated luminescence chronologies, and U-Pb detrital zircon and Ar-Ar mica provenance fingerprinting, we constrain the timing and sources of the fluvial deposits. When dove-tailed with sedimentological analysis, our results demonstrate how river morphodynamics influenced Indus settlement patterns albeit in a counterintuitive fashion.