Temporally staggered formation of the Middle Pleistocene terrace in the Gonghe Basin (northeastern Tibetan Plateau) and the evolution of the Upper Yellow River

The Gonghe Basin, situated in the northeastern Tibetan Plateau, preserves multiple terrace levels formed by the Yellow River, which are critical for understanding the regional tectonic-climatic histories and integration processes of the Upper Yellow River. However, the chronology of these terraces—particularly the extensive First, Second, and Third Tala surfaces, which represent different stages of the basin’s geomorphological and fluvial evolution—remains a subject of debate due to conflicting dating results spanning the Early Pleistocene to the Late Epipleistocene. This study addresses this geomorphic and chronological question by focusing on the Second Tala Surface, utilizing terrestrial in situ cosmogenic nuclide (TCN) and optically stimulated luminescence (OSL) dating methods to ascertain its formation age and the fluvial processes involved. Two 10Be profiles (samples STL01 and STL02) were strategically targeted at the leading and trailing edges of the Second Tala Surface. In addition, OSL samples were collected to account for the influence of loess cover on nuclide production. Our results reveal depositional cessation ages of 131.26 ± 5.82 ka and 370.87 ± 22.54 ka for STL01 and STL02, respectively. These chronological results suggest that the Yellow River had experienced significant lateral erosion and floodplain expansion prior to the formation of the Second Tala Surface. Regarding the younger age as the abandonment age of the Second Tala Surface, our results suggest that glacial−interglacial transitions and regional tectonic activities played a crucial role in the abandonment of the regional geomorphic surface. This research further provides new insights into the geomorphic evolution of the Upper Yellow River and highlights the dynamic interplay among tectonic deformation, climatic fluctuations, and fluvial reorganization in shaping the regional landscape.