Abstract
Urbanism in the Bronze-age Indus Civilisation (~4.6–3.9 thousand years before the present, ka) has been linked to water resources provided by large Himalayan river systems, although the largest concentrations of urban-scale Indus settlements are located far from extant Himalayan rivers. Here we analyse the sedimentary architecture, chronology and provenance of a major palaeochannel associated with many of these settlements. We show that the palaeochannel is a former course of the Sutlej River, the third largest of the present-day Himalayan rivers. Using optically stimulated luminescence dating of sand grains, we demonstrate that flow of the Sutlej in this course terminated considerably earlier than Indus occupation, with diversion to its present course complete shortly after ~8 ka. Indus urban settlements thus developed along an abandoned river valley rather than an active Himalayan river. Confinement of the Sutlej to its present incised course after ~8 ka likely reduced its propensity to re-route frequently thus enabling long-term stability for Indus settlements sited along the relict palaeochannel.
Highlights
Urbanism in the Bronze-age Indus Civilisation (~4.6–3.9 thousand years before the present, ka) has been linked to water resources provided by large Himalayan river systems, the largest concentrations of urban-scale Indus settlements are located far from extant Himalayan rivers
It is commonly accepted that settlements are clustered near active rivers and that river avulsion leads to settlement abandonment[3]; this has been offered as an explanation for spatiotemporal changes in urban settlement patterns[4, 12, 13], but this mechanism cannot be tested, unless the timing of major avulsions is known
Urbanism in the Indus Civilisation is associated with the development of five large settlements considered by archaeologists as cities, and numerous smaller urban settlements that are characterised by distinctive architectural elements and material culture[15, 16, 18]
Summary
Sensed imaging of the Ghaggar–Hakra palaeochannel. To map the large-scale modern and palaeo-drainage configuration of the region, we analysed the geomorphology using remotely sensed optical imagery and a Synthetic Aperture Radar (SAR)derived digital elevation model (DEM) focussing in particular on the Ghaggar–Hakra palaeochannel. Our analysis suggests that the darker blue tone represents relatively cooler and less reflective surface materials, interpreted as sediments with higher moisture content We interpret this damp and sinuous feature to represent the trace of the Ghaggar–Hakra palaeo-drainage system. Analysis of a relative elevation map derived from these data (Fig. 3) shows that the Ghaggar–Hakra palaeochannel observed in the colour composite image data corresponds to a topographic low in the landscape. This indicates that the palaeochannel forms an elongate and sinuous incised valley that is eroded several metres into the surrounding plains (Fig. 3)
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