How headward erosion breaches upstream paleolakes: Insights from dated longitudinal fluvial terrace correlations within the Sanmen Gorge, Yellow River.

Headward erosion breaching a formerly closed paleolake has been interpreted as an integration process between individual drainage networks. However, the rarity of well-documented cases of this process makes it difficult to explore the fluvial response or its mechanism. Fortunately, dated deposits from a former paleolake in the Fenwei Basin, coupled with fluvial terraces along the Sanmen Gorge of the Yellow River, provide ample opportunities to replicate the upstream integration process and associated landform response. Herein, we applied terrace correlation and age constraints to construct dated longitudinal profiles throughout the Fenwei Basin and the downstream Sanmen Gorge. We identified two age models in longitudinal profiles: (1) relatively high diachronous terraces (Terrace series A) aged headward from ca. 621 ka to 336 ka, localized in the Sanmen Gorge; and (2) relatively low isochronous terraces (Terrace series B) capped by S2 paleosol (ca. 245-190 ka) developed throughout the basin and the gorge. This study hypothesized these two terrace series to have emerged as a mid-Pleistocene bottom-up integration event. In this event, headward incision initiated at least at ca. 621 ka, progressed upstream at a rate of 79.8 mm/a, and breached the Fenwei Basin at ca. 245 ka. This event is likely ascribed to tectonic subsidence of the North China Plain, and may be the latest integration process between the middle and lower reach of the Yellow River. We synthesize comprehensive models to describe terrace genesis and responses in tectonic, climatic, and bottom-up integration processes, which could widen our understanding of long-term large river behaviors. [ABSTRACT FROM AUTHOR]