Stable isotopic composition of pedogenic carbonates from the eastern margin of the Thar Desert, Rajasthan, India

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 C4 biomass (grasses?) has dominated local vegetation for most of the 250,000 years represented by the 16R section. Our results display a decrease in δ18O and δ13C values during the last interglacial and early glacial periods. The higher δ13C 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 δ13C values may, therefore, denote the expansion of C4 vegetation in response to warm, wetter monsoon circulation. Conversely, low δ18O and δ13C values mark the expansion of C3 vegetation, probably caused by enhanced winter rains and lower temperatures.