Geochemical and Sr–Nd isotope clues to the widespread subaerial dispersal of sandy desert sediments influenced by spatially variable sorting and weathering processes

ABSTRACT Understanding the subaerial dispersal of desert sediments along a downwind aridity gradient is challenging but crucial for promising sustainability in habitable semiarid boundary regions. The Thar Desert of Rajasthan (India) emits copious fine dust towards the Himalayas before the onset of the Indian Summer Monsoon every year. However, the climatic influence (especially of eolian processes and aridity conditions) on the provenance characteristics, downwind dispersal, and postdepositional alteration of sandy sediments across the desert is poorly understood. This knowledge is essential for reliable provenance tracing in arid and semiarid environments. For this purpose, 52 surface sediment samples, spanning the hyperarid southwestern area to the semiarid eastern and northeastern fringes of Rajasthan, have been characterized for geochemical, isotope, mineralogical, and grain-size data. The measured properties reveal a consistent upwind provenance of sandy sediments across the desert, as well as the variable impacts of wind forcing, elevation, and aridity conditions. The Thar sediment signatures from upwind Jaisalmer and Barmer districts can be reliably traced at downwind locations in the Jhunjhunu, Churu, and Jaipur districts. The dune-profile sediments from Jhunjhunu and Rajgarh (Churu), located in the northeastern semiarid fringes, are more weathered chemically and show higher Zr abundances and lower εNd than the other samples. Notably, higher 87Sr/86Sr and quartz enrichment are found in fine sand, especially from the Aravalli highlands. The plausible reason for the grain-size variability of Sr isotopes seems to be K-feldspar or mica preferentially retained in fine sand delivered to highlands under stormy conditions. This study highlights the widespread eolian transport of sandy Thar sediments to downwind locations at distances of ∼ 400–500 km. The widespread Thar sediment dispersal is also accompanied by spatially variable grain size, mineral sorting, and postdepositional chemical weathering under favorable conditions. The modification in geochemical and isotope compositions of widespread desert sediments owing to spatially varying sedimentary processes needs to be accounted for in future provenance studies of downwind eolian sediments.