Evolution of the Indian summer monsoon: synthesis of continental records

Abstract

Fluvial sediments of the Siwalik succession in the Himalayan Foreland Basin form the most important continental archive for reconstructing monsoonal fluctuations during the Late Miocene to Late Pleistocene. A number of proxy records suggest multiple phases of monsoonal intensification with peaks at 10.5, 5.5 and 3 Ma after which the strength of the monsoon decreased to modern day values with minor fluctuations. Detailed evaluation of Late Quaternary interfluve stratigraphic development in the Ganga plains shows that interfluve areas near the major rivers aggraded periodically between 27 and 90 ka. They subsequently degraded or accumulated sediment only locally, probably reflecting decreased monsoonal precipitation around the Last Glacial Maximum. Increased precipitation during the 15 to 5 ka period of monsoon recovery probably increased discharge and promoted incision and widespread badland formation. In western India, the fluvial records back to c. 128 ka suggest a stronger monsoon around 80 ka followed by periods of weakened monsoon around 70 to 30 ka and progressive desiccation in the glacial period. Holocene lacustrine records from western Rajasthan suggest maximum lake levels at c. 6 ka and complete desiccation between c. 3 and 4 ka.