Fluvial entrenchment of the Gonghe Basin and integration of the upper Yellow River-Evidence from the cosmogenically dated geomorphic surfaces

The geomorphic evolution of the Yellow River, especially its upper reach, contains critical information on the tectonic activity and climatic change within and around the northeastern Tibetan Plateau, and even matters in understanding the effects of regional disaster chain. However, the integration history of the upper Yellow River and its related connections with drainage reaches inside and outside the Tibetan Plateau remain indistinct. The main controversy lies in the excavation times of some upper-reach basin systems. The Gonghe Basin, located within the northeastern Tibetan Plateau, has long been considered one of the most pivotal areas providing insights into the evolution of the upper Yellow River. In this study, we report two cosmogenic burial ages regarding the abandonment of the geomorphic surfaces within the Gonghe Basin. The two selected geomorphic surfaces are the abandoned connecting pass between Gonghe and Guide Basins (i.e., the Gahaitan channel), and the topmost Yellow River terrace in the Gonghe Basin known as the Third Tala surface. Our results show that the Gahaitan channel and the Third Tala surface were abandoned at 1.17 +/- 0.10 Ma and 0.76 +/- 0.12 Ma respectively, denoting its excavation by the incision of the Yellow River in the late Early Pleistocene period. Our analysis takes into account regional fault activities, landscape adjustment, and global climate fluctuations, indicating that the excavation was jointly influenced by regional fault activities and the glacial-interglacial cyclicity during the MidPleistocene Transition. When integrated with evidence from river terraces in upstream and downstream regions, our results indicate that the integration of the upper Yellow River behaves a roughly headward erosion pattern from the Plateau margin, while the integration process appears to be heterogeneous. At last, the integration history of the upper Yellow River was further explored.