Provenance of the Neogene Deposits in the Western Himalayan Foreland Basin: Implications for Drainage Reorganization During the Late Miocene Uplift of the Himalaya.

Interaction between large‐scale tectonics and the Indian summer monsoon plays a key role in shaping drainage system of major Himalayan rivers. The Neogene‒Quaternary fill of the Himalayan foreland‐basin system holds critical constraints in their sedimentary archive for understanding these interactions. In this study we use detrital‐zircon U‐Pb geochronology and bulk rock Sr‐Nd‐Hf isotope data for tracking sediment sources of the Neogene fluvial succession of the Kasauli Formation and the Siwalik Group in the Subathu Basin of the Western Himalayan foreland. Comparison of results from this study and other previous detrital records from equivalent sedimentary successions of adjacent foreland basins of the western Himalaya point to substantial variability of provenance signal along the strike of the orogen. Marked occurrence of 40–110 Ma zircon population appearing at recurrent intervals within the Siwalik Group points to a sediment sourcing in the Trans‐Himalayan Batholith. Here, we evaluate possible paleo drainage architecture responsible for cross‐orogen sediment transport to the foreland basin. We propose that an ancestral drainage of the modern Sutlej River, routed these magmatic arc‐derived sediments across the Himalaya to the Subathu Basin. Zircon geochronology data suggest that this transverse dispersal system was particularly effective during the deposition of Middle Siwalik Formation (ca.11–4.5 Ma). On the other hand, the small‐scale fluctuations in the presence of the Trans‐Himalayan zircons observed in the Lower and Upper Siwalik formations may primarily reflect climatic forcing, which induced changing monsoon precipitation and the Sutlej's transport capacity between dry and moist periods. Key Points: Detrital‐zircon geochronology of the Neogene deposits in Subathu Basin reflects exhumation of the Higher Himalayan Crystalline SequenceThe Siwalik Group in Subathu Basin reveals Trans‐Himalayan magmatic arc‐derived zircons among major detrital componentsA transverse drainage system likely facilitated transport of arc detritus to the foreland basin across the Himalaya [ABSTRACT FROM AUTHOR]