Tectonic and climatic controls for fluvial terraces of the Yellow River over the past 2.6 Ma at Northeast Tibetan Plateau and Ordos Block

The Yellow River is usually assumed to record tectonic activities and climatic changes; however, a systematic study was lack in the sedimentology, stratigraphy, geomorphology and geochronology for the entire Yellow River though various geologic scholars have conducted numerous works in individual basins. This review focused on well-preserved fluvial terrace sequences that formed along this river on northeastern (NE) Tibetan Plateau and Ordos Block over the past 2.6 Ma. After comparing numerous initial incision ages at different segments along the Yellow River, we found out that the youngest initial incision may occur at ca. 150 ka at the Longyang Gorge. The Yellow River may transit from multiple separated endorheic drainages to an entire external drainage after 150 ka, which may cause differentiations in the apparent incision rates before and after 150 ka; thus apparent net incision rates were calculated respectively for the Yellow River before 150 ka and the drainage network post 150 ka. Apparent net incision rates prior to 0.15 Ma were calculated as 0.15, 0.29, 0.10, 0.12 and 0.03 mm/a respectively in Tongde-Xunhua, Lanzhou-Linxia basins, Heishan, Jinshan and Fenwei-Sanmen Gorges in this review, which mainly reflected Kunhuang-Gonghe Tectonic Event, generated by the Indo-Asian collision and diminishing as the NE Tibetan Plateau eastward extruding at ca. 1.8–0.15 Ma. Apparent net incision rates post 0.15 Ma were calculated respectively for NE Tibetan Plateau and Ordos Block, considering their different base level. On NE Tibetan Plateau, four fluvial degradational phases were identified between ca.105∼70, 53∼40, 25∼16 and 12∼6 ka associated with terrace levels respectively, at average elevations of 96, 40, 20 and 10.5 meters above the current river level (m arl) within a range of 5 ∼ 96 m arl; and four broad periods in the last 150 ka on Ordos Block: possibly marine oxygen isotope stage (MIS) 5, ca. 118 to 72 ka, most of MIS 3, ca. 44∼28 ka, transition from LGM to last deglacial ca. 20 to 16 ka, and 4∼3 ka at average elevations of 67.5, 26, 19 and 11.5 m arl. These degradational phases post 0.15 Ma were associated with multiple processes including enhanced fluvial discharge with an increase in monsoonal precipitation and/or melt water in deglaciation.