Playas of the Thar Desert: Mineralogical and Geochemical Archives of Late Holocene Climate*

Abstract

This study presents a synthesis of the published data and summarizes new data on mineralogy and geochemistry of the late Holocene playa sediments from the Thar Desert, located in the down stream of southwest monsoon. The eastern margin of the Desert is semi-arid (>400 mm a -1 ), whereas the western region is arid (200-300 mm a -1 ). The negative water budget (higher evapo-transpiration/precipitation) has led to the presence of a number of playas in the region. The assemblage of clastic minerals is similar and constitutes quartz, plagioclase, K-feldspar, amphibole, mica and chlorite. The non-clastic mineral assemblage is variable and comprises of both evaporite minerals and carbonates. The geochemical proxies enabled differentiation of the shallow depth profiles at five different playas into horizons of varying chemical weathering, aeolian input and evaporation. Between ca.1.3-3.1 ka, the dominance of proto-dolomite, [Ca >1 (Fe,Mg) (CO 3 ) 2 ] in the eastern playas and presence of gypsum (CaSO 4 .2H 2 O) in the western playas suggest that the present day climatic gradient might be exiting during the late Holocene.