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 San -men Gorge of the Yellow River, provide am-ple opportunities to replicate the upstream integration process and associated landform response. Herein, we applied terrace correla-tion 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 ter-races (Terrace series A) aged headward from ca. 621 ka to 336 ka, localized in the Sanmen Gorge; and (2) relatively low isochronous ter-races (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 Fen-wei Basin at ca. 245 ka. This event is likely ascribed to tectonic subsidence of the North China Plain, and may be the latest integra-tion 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.

Automated summary

This study examines a former paleolake in the Yellow River, and identifies two different-age terraces through terrace correlation and age constraints. It suggests that this was a mid-Pleistocene bottom-up integration event, likely caused by tectonic subsidence. The findings contribute to our understanding of long-term behaviors of large rivers.