STABLE ISOTOPIC COMPOSITION OF PEDOGENIC CARBONATES FROM THE EASTERN MARGIN OF THE THAR DESERT, RAJASTHAN, INDIA

Pedogenic carbonates in a 19m-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 d ¹⁸O and d ¹³C values during the last interglacial and early glacial periods. The higher d ¹³C 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 d ¹³C values may therefore denote the expansion of C₄ vegetation in response to warm, wetter monsoon circulation. Conversely, low d ¹⁸O and d ¹³C values mark the expansion of C3 vegetation, probably caused by stronger winter rains and lower temperatures.