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Pedogenic carbonates in a 19 m-thick dune section (16R) at Didwana, and several shorter profiles from the eastern margin of the Thar Desert, Rajasthan, were studied for their stable isotope composition. Carbon isotope results show the C-4 biomass (grasses?) has dominated local vegetation for most of the 250,000 years represented by the 16R section. Our results display a decrease in delta O-18 and delta C-13 values during the last interglacial and early glacial periods. The higher delta C-13 values in our dune records correlate to episodes in the strong upwelling and decreased sedimentation rates in Indian Ocean cores, probably the result of a strong Asian Monsoon. The high delta C-13 values may, therefore, denote the expansion of C-4 vegetation in response to warm, wetter monsoon circulation. Conversely, low delta O-18 and delta C-13 values mark the expansion of C-3 vegetation, probably caused by enhanced winter rains and lower temperatures. (c) 2007 Published by Elsevier Ltd.