Luminescence chronology of river adjustment and incision of Quaternary sediments in the alluvial plain of the Sabarmati River, north Gujarat, India

River adjustment and incision in the Sabarmati basin, Gujarat, India have b een examined at a site near Mahudi. Towards this, the morphostratigraphy an d depositional chronometry of the middle alluvial plains were investigated. The upper fluvial sequence, along with the overlying aeolian sand and rive rbed scroll plains, provide clues to the evolution of the present Sabarmati River. Sedimentological analyses of the upper fluvial sequence indicate it s deposition by a meandering river system during what is believed to be a p ersistent wetter phase. Luminescence chronology bracketed this sequence to between 54 and 30 ka, which corresponds to Oxygen Isotope Stage-3, during w hich the SW monsoon was enhanced. The overlying aeolian sand has been dated to 12 ka, indicating that dune accretion occurred simultaneously with the strengthening of the SW monsoon during the Early Holocene. Adjustment of th e Sabarmati along a N-S transect is placed wound 12 ka and the incision is bracketed between 12 and 4.5 ka. River adjustment could have been tectonic: however, the incision was Facilitated by the availability of continuous fl ow in the river caused by the SW monsoon. The basin experienced two tectoni c events at about 3 and 0.3 ka, as demonstrated by the morphology of the sc roll plains. (C) 2001 Elsevier Science B.V. All rights reserved.