Climatic influence on sediment distribution and transport in the Thar Desert (Sindh and Cholistan, Pakistan)

The Thar Desert is a major sediment depocenter located in southwestern Asia and bordering the Indus drainage system to its east. It is unclear where the sediment that built the desert is coming from, and when the desert experienced phases of construction. In particular, we seek to establish the role of the South Asian monsoon in the initial formation and subsequent expansion of the desert. Here we integrate bulk-petrography and heavy-mineral data with U-Pb ages of detrital zircon grains to understand how the Thar Desert relates to the major potential sediment sources in the Himalayan orogen and to the large rivers that adjoin it to the west and north. Bulk petrography and heavy-mineral data from eolian sand in Cholistan (NE Pakistan) show closer similarity with that of Himalayan tributaries than eolian sand in Sindh (S Pakistan), which contains heavy-mineral suites close to those of mainstream Indus sand largely supplied by erosion of the Karakorum and Kohistan ranges. Kohistan is a particularly rich source of heavy minerals and is thus over-represented in provenance budgets based on that proxy alone. U[sbnd]Pb ages of detrital-zircon fail to show a sharp difference between dune sands in Sindh and Cholistan but confirms a somewhat greater supply from the Himalaya in Cholistan and from the Karakorum, Kohistan, and Nanga Parbat in Sindh. Zircon ages are similar in Sindh desert sand and in the Indus Delta, and are most similar to deltaic sand dated as 7 ka or older in the deglacial period. In parallel, the age signature of Cholistan sand resembles more that of older river channels found along the northwestern edge of the desert (e.g., paleo-Ghaggar-Hakra) than that of modern Himalayan tributaries (e.g., Sutlej). Both Cholistan and Sindh sands suggest that sediment supply to the desert was greater during the early Holocene when the summer monsoon was stronger. The southwesterly summer monsoon was the most effective agent of eolian transport and recycling of Indus delta sediments entrained towards the central and northern parts of the Thar Desert.