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The Yellow River (YR) is one of the longest and most sediment-laden rivers in the world. However, the timing and mechanism of the integration of upstream and downstream reaches of the YR is still debated, with estimates ranging from >34 Ma to ~0.15 Ma. Here we address this debate by studying the detrital-zircon age spectra from three boreholes that penetrate late Miocene sediment in the lower YR floodplain. Our results show a significant provenance change between 1.6 and 1.5 Ma marking the input of new materials from the Middle Reach and/or the Upper Reach, suggesting the upstream and downstream parts of the YR were connected between 1.6 and 1.5 Ma. This late establishment of the YR is not consistent with the timing of uplift of the northeastern Tibetan Plateau and surrounding mountain ranges and thus precludes a tectonic control; however, it follows the Plio-Pleistocene onset of large-amplitude sea level changes, associated with a worldwide increase of fluvial incision. We propose that Plio-Pleistocene base level fluctuations likely triggered fluvial erosion propagating upstream from the YR lower reach and were thus the main driving force for river integration.
•Detrital-zircon evidence shows the YR became integrated between 1.6 and 1.5 Ma.•Integration of the YR was likely forced by increase in amplitude of sea-level changes.•Integration of the YR may have driven deserts expansion across the northwestern China.