Provenance of Thal Desert sand: Focused erosion in the western Himalayan syntaxis and foreland-basin deposition driven by latest Quaternary climate change

As a latest Pleistocene repository of Indus River sand at the entry point to the Himalayan foreland basin, the Thal dune field in northern Pakistan stores crucial information that can be used to reconstruct the erosional evolution of the Himalayan-Karakorum orogen and the changes in the foreland-basin landscape that took place between the Last Glacial Maximum and the early Holocene. This comprehensive provenance study of Thal Desert sand integrates previously existing petrographic, heavy-mineral, mineral-chemical, isotopic, and geochronological databases with original bulk-sediment geochemistry, zircon-age, and Nd-isotope data. Dune sand is low in quartz and rich in feldspars, volcanic, metavolcanic and metabasite grains, contains a very rich transparent heavy-mineral suite including hypersthene and common zircon grains dated as Late Cretaceous to early Paleogene, and is characterized by high Mg, Sc, V, Co, Ni, Cu concentrations and by εNd values as high as −3.5. Together, these data indicate that ~40% of Thal dune sand was supplied by erosion of the Kohistan arc, a proportion that far exceeds the one assessed for modern Upper Indus sand. Greater detrital supply from the Kohistan arc indicates notably different conditions of sediment generation, during a period in which the sediment-transport capacity of the Upper Indus in the dry lowlands was reduced and volumes of sand were extensively reworked by wind and accumulated in dune fields across the foreland basin. In the early Holocene, the renewed strength of the South Asian monsoon and consequently markedly increased water and sediment discharge led to incision of the Thal and Thar dune fields by the Indus River and its Punjab tributaries draining the Himalayan front directly hit by heavy monsoonal rains.