Coupled Glacial, Fluvial and Aeolian Processes Induced Provenance Shift of Sandy Deserts Surrounding the Northeastern Tibetan Plateau

The Badain Jaran Desert hosts the world's tallest mega‐dunes, but its long‐term sand sources remain poorly constrained, limiting insights into its evolutionary mechanisms. Geochemical fingerprints of multiple grain‐size fractions from a centrally located borehole yielded a ∼1.2 Ma provenance record: early sediments derived mainly from the Central Asian Orogenic Belt (CAOB), whereas after ∼0.7 Ma the northeastern Tibetan Plateau (NETP) became the dominant source. This transition, synchronous with provenance changes in the adjacent Tengger Desert, reflects expanded glaciation and intensified fluvial activity on the NETP. These environmental changes were driven by global cooling and Northern Hemisphere glaciation following the Mid‐Pleistocene Transition, which together increased detritus production and transport. Concurrently, a strengthened East Asian Winter Monsoon enhanced delivery of glacial–fluvial sediments to the desert. These coupled glacial–fluvial–aeolian processes created favorable conditions for mega‐dune growth and played a pivotal role in shaping the sand seas surrounding the NETP.