Tracing Sediment Pathways in the Siang Basin: A Multi-Proxy Provenance Approach Using Petrography, Zircon Geochronology, and Sr–Nd Isotopes

Understanding sediment provenance is crucial for reconstructing past environmental conditions and deciphering erosion patterns in rapidly evolving mountain belts such as the Himalaya. The Yarlung–Tsangpo–Brahmaputra system, one of the world’s most dynamic sediment-routing networks, provides a key setting to examine how extreme hydrological events mobilize material from distinct source terranes. In this study, we analyse five well-dated paleoflood deposits from the Siang River using an integrated suite of provenance tools—sand petrography, U–Pb zircon geochronology, and Sr–Nd isotope geochemistry—to evaluate their relative strengths and interpretive limitations.

Petrographic data show quartz–feldspar-rich compositions and heavy-mineral assemblages pointing to contributions from the Higher Himalayan Crystallines (HHC) and Tethyan Sedimentary Sequence (TSS), although long-distance transport, weathering, and hydraulic sorting obscure lithologic specificity. Zircon age spectra reveal diverse age populations sourced from the Namche Barwa syntaxis, Tibetan Plateau, and Lhasa Terrane; however, zircon recycling and overlapping age groups introduce ambiguity in resolving discrete source areas. Sr–Nd isotopic signatures provide a more integrated and transport-insensitive signal, indicating dominant TSS influence with enhanced erosion of the Namche Barwa region during high-magnitude flood events. Together, these proxies demonstrate that each method captures a different scale of sediment input—petrography reflecting local lithologic contributions, zircon ages tracing distal and recycled sources, and Sr–Nd isotopes integrating basin-scale signatures. The multi-proxy approach underscores the need to combine complementary datasets to accurately reconstruct sediment routing, identify erosional hotspots, and comprehend megaflood-driven landscape evolution in the eastern Himalayas.