Mid-Pleistocene formation of the Yellow River fluvial megafan

The lower Yellow River (YR) has historically experienced dramatic course shifts over the North China Plain (NCP), depositing natural resources and nurturing human civilization. These shifts, however, also drive recurrent natural disasters. Understanding the timing and mechanisms of these course changes is essential for effective disaster mitigation and resource acquisition. Through integrated geomorphic and sedimentological evidence, we identify the lower YR deposits as one of the world’s largest fluvial megafans, with its dynamic course shifts explained by megafan theory. Sedimentological data and a paleomagnetic age model show that the megafan formed at ∼1.5 Ma, during the gradual ascension of 100-kyr climate cycles and amplified glacial-interglacial fluctuations. We propose that this global climatic shift facilitated the integration of the middle YR, enhancing its erosive capacity to breach the Sanmen Gorge and connecting the middle and lower reaches. This challenges prior hypotheses of headward erosion of the lower YR as the primary driver of the middle and lower YR integration. Since ∼1.5 Ma, sediment accumulation on the NCP has rendered it one of the most flood-prone regions, characterized by a prominent super-elevated aggrading river. The presence of the lower YR megafan indicates substantial terrestrial sediment storage, encouraging the reassessment of marginal-sea sediment accumulation rates for estimating inland erosion.