Playas of the Thar Desert: Mineralogical and GeochemicalArchives of Late Holocene Climate

摘要

This study presents a synthesis of the published data and summarizes new dataon 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 negativewater budget (higher evapo-transpiration/precipitation) has led to the presence of a numberof playas in the region. The assemblage of elastic minerals is similar and constitutes quartz,plagioclase, K-feldspar, amphibole, mica and chlorite. The non-clastic mineral assemblageis variable and comprises of both evaporite minerals and carbonates. The geochemical proxiesenabled differentiation of the shallow depth profiles at five different playas into horizonsof varying chemical weathering, aeolian input and evaporation. Between ca.1.3-3.1 ka, thedominance of proto-dolomite, [Ca_(>1)(Fe,Mg)_(<1)(CO_3)_2] in the eastern playas and presence ofgypsum (CaSO_42H_2O) in the western playas suggest that present day climatic gradientmight be exiting during the late Holocene.