This study investigated sediment source to sink relating the channelization of the Yangtze River into the sea. A sediment borehole (PD) on the river coast, penetrating thick Quaternary sediments, to thin sediments of late Pliocene age until the bedrock recorded a change in sediment provenances through time. Geochemical elements and magneto-stratigraphy helped identify five zones. Zone I (the late Pliocene-the Early Pleistocene), characterized by Pb, Th, U, Ba, La, Ce, Nd, Hf, Y, Zr, Nb and Mn, indicated a local sediment provenance. This means that the study area was a localized sub-basin. Zone II (the Early Pleistocene-the mid-stage of Early Pleistocene), with remarkable high Fe, K, As and Rb implied a new sediment provenance joining to the sub-basin from the middle Yangtze reach after the opening of Zhenjiang Gorge. Zone III (the mid-stage of Early Pleistocene-the Middle Pleistocene), featured by Ti, V, Cr, Sr, Sc, Cu, Co, Ni, Mg, Ca, Na and P suggested a further extension of sediment provenance to the upper Yangtze reach, where a large block of the E’mei basalt occurs. This hinted the channelization of the Three Gorges valley linking the upper and middle Yangtze reaches. Zone IV~V (the Middle Pleistocene-the Holocene) showed their geochemical similarity to Zone III. Discrimination ratio f(Cr,Th), f(La) and f(K,La), a new approach developed for tracing sediment provenance, confirmed a basin-wide sediment source through Zone III-V. These together witness a progressive extension of the sediment provenance towards the upper Yangtze reach, corresponding to the long-term tilting effect of the Cenozoic Topographic Reversal of the eastern China continent. The timing of the Yangtze River channelizing into the continental shelf of East Asia appeared at ca. 1.0~1.2 Ma (bottom of Zone III).