River response to Quaternary climatic fluctuations: evidence from the Son and Belan valleys, north-central India

Abstract

The last glacial period was cold and dry in peninsular India. In north-central India, the interval from 39±9 to 16±3 ka was associated with widespread and prolonged aggradation in the Son and Belan valleys. The aggradation ended with sustained vertical incision after 16±3 ka and reflects a return to warmer, wetter conditions. In this region, it would appear that terminal Pleistocene to Holocene river incision was broadly synchronous with a strong summer monsoon regime and higher levels of river discharge and the preceding river aggradation with lower discharge and a weaker or more variable summer monsoon regime. Two older phases of prolonged aggradation followed by vertical incision are evident in the Son and Belan valleys before ~39 ka. One of these phases is centred towards 73±4 ka when ash from the Toba mega-eruption in Sumatra was deposited across peninsular India. The following phase of aggradation has yielded infrared stimulated luminescence ages of 58±6 and 45±12 ka. The youngest phase of aggradation began towards ~5.5 ka and seems to mark a return to a weaker summer monsoon regime.