Tracing South Asian monsoon variability through a late miocene record from the himalayan foreland basin

The relative contributions of global cooling and tectonic forcing to the reorganization of the South Asian monsoon during the critical Late Miocene remain poorly constrained. By analyzing sedimentological and geochemical proxies from the Tanakpur-Sukhidang section in the Himalayan foreland basin, we reconstruct paleoclimatic conditions to infer South Asian monsoon variability during this period. The enrichment of LREEs, a flat HREEs pattern and a negative Eu anomaly, along with elemental ratios of La/Sc and Th/Co, suggest a persistent felsic source derived from the Himalaya since ~12 Ma. Clay mineral variations, particularly the shift in smectite content and smectite/(illite + chlorite) ratio, together with geochemical weathering indicators (CIA, WIP and Rb/Sr), document a relative increase in chemical weathering around 8 Ma. These mineralogical and geochemical transformations are synchronous with widespread indicators of South Asian monsoon weakening linked with change in exhumation rate of the Himalayan-Tibetan Plateau and Late Miocene global cooling. Where reduced physical erosion and enhanced sediment-water interaction under cooler and more seasonal conditions amplified chemical weathering feedbacks. Together, these processes reorganized regional hydrology and monsoon dynamics, underscoring the coupled influence of tectonics and global climate forcing in driving the Late Miocene weakening of the South Asian monsoon. However, the relative influence of climate versus tectonics still remains inherently very complex and higher resolution provenance data, thermochronology and climate model simulations will be crucial for fully understanding the mechanisms underlying the Late Miocene Change.