Magnetostratigraphic dating of river terraces: Rapid and intermittent incision by the Yellow River of the northeastern margin of the Tibetan Plateau during the Quaternary

Up to 23 paleosols have been identified in loess sequences that overlie fluviatile sediments on seven terraces of Huang He (the Yellow River) and Daxia He in the Linxia Basin at the northeastern margin of the Tibetan Plateau. The magnetostratigraphic record in the oldest sequence appears to be fairly complete and spans the entire Quaternary. It includes evidence for the Jaramillo and Olduvai normal polarity subchrons within the Matuyama chron, as well as the Cobb Mountain and “stage 54” (formerly Gilsa) events. Age constraints within the Brunhes are provided by 14C and thermoluminescence/optical stimulated luminescence dating. The magnetostratigraphic chronology of the Quaternary sediments indicates that terraces were formed at about 1.66, 1.4, 1.1, 0.6, 0.12, 0.055, and 0.01 Ma. The terraces may represent climatically induced pauses in long‐term tectonically induced incision by the rivers. On the basis of terrace heights and ages, incision rates were highest from 1.66 to 1.4 Ma (∼1 m/kyr), decreased from 1.4 to 0.12 Ma (∼ 0.1 m/kyr), and increased from 0.12 Ma to present (∼0.75 m/kyr). If river incision is attributed solely to uplift of the Tibetan Plateau, then this uplift appears to have been rapid as well as intermittent following the first evidence of the existence of Huang He in this area at about 1.75 Ma. However, the effects of uplift cannot be fully separated from incision caused by changes in climate.