Terrace sequence along the Yellow River of the Xinghai section in the northeastern Tibetan Plateau: Implications for evolution of the upper Yellow River since the Pliocene

River terraces serve as important geomorphic and sedimentary archives， recording the long-term evolution of fluvial systems and providing key insights into tectonic activity and paleoclimatic changes. In this study， we investigate the river terraces developed within the Xinghai Basin， located in the upper reaches of the Yellow River on the northeastern Tibetan Plateau. Based on extensive field investigations， optically stimulated luminescence (OSL) dating， and integration of previously published chronological data， we identify eight terrace levels. These terraces are dated to approximately 2.0 ka， 3.6 ka， 34 ka， 109 ka， 116 ka， 132 ka， 140 ka， and 200 ka. The oldest terraces correlate temporally with the Gonghe tectonic movement. Following ～140 ka， a significant increase in river incision rates is observed， from 1.3 mm/a to 11.6 mm/a， which we interpret as a response to intensified climatic variability superimposed on tectonic uplift. These findings suggest that the formation of fluvial terraces in the Xinghai Basin is jointly controlled by climatic oscillations and tectonic processes. Furthermore， the results indicate that the drainage evolution of the upper Yellow River has been characterized by ongoing headward erosion and drainage reorganization.