A thriving early-mid Holocene river? Emerging geochronological evidence from the Luni River floodout zone, northwestern India

The Luni River arises in the Ajmer district of Rajasthan, India, and demarcates the eastern boundary of the Thar Desert. In its lower reaches, a floodout zone ~60 km long and up to 20 km wide hosts an extensive network of active and abandoned channels, many of which terminate in the Rann of Kutch. Previous studies of the region’s aeolian dunes, river terraces and palaeochannels, lake cores and marine deposits indicate a stronger South Asian Summer Monsoon in the late Pleistocene to mid Holocene, with aridification then triggering landscape changes across the desert, but so far, the chronology of the Luni floodout zone has remained unknown. Large palaeochannels identified using remotely sensed datasets, and preliminary geochronological data, provide evidence for a previously more vigorous river system, suggesting major hydroclimatic shifts. To build a robust geochronological framework highlighting periods of channel aggradation, sediment samples for Optically Stimulated Luminescence (OSL) dating (n = 38) have been collected from active and abandoned channel beds and banks within the floodout zone. OSL analyses are ongoing but are expected to indicate enhanced fluvial activity in early-mid Holocene and declining activity in the late Holocene, leading to development of the floodout zone. Archival data (e.g. the first scientific maps published by Survey of India) will provide evidence of historical changes (over the last 200 years). The findings will contribute new insights into Thar Desert landscape development and archaeology (Indus Valley Civilisation) and also enhance an emerging global picture of dryland river response to Holocene hydroclimatic changes.