Stable oxygen and carbon isotope record from a drill core from the Hetao Basin in the upper reaches of the Yellow River in northern China and its implications for paleolake evolution
Knowledge of the evolution of the paleolakes that developed intermittently within the Hetao Basin in northern China is important for understanding both the evolution of the upper and middle reaches of the Yellow River drainage system and the spatio-temporal evolution of regional water vapor transport associated with the East Asian summer monsoon. However, the long-term history of these lakes and the driving mechanisms are poorly understood. In this study, we reconstructed the history of the paleolakes within the Hetao Basin over the past ~1.68 Myr, based on δ18O and δ13C records from lacustrine authigenic carbonates in a 274.60-m-long drill core from the centre of the Hetao Basin. The absence of covariation of carbonate δ18O and δ13C during the intervals of ~1.47–1.30 Ma and ~1.17–1.07 Ma suggests the existence of a hydrologically-open lake system in the Hetao Basin. The relatively low and invariant carbonate δ18O values are similar to those of the modern Yellow River water, suggesting that the paleolakes formed when the lakes and the Yellow River were connected. The moderately high correlation (r = 0.61) of carbonate δ18O and δ13C during ~0.68–0.60 Ma suggests an intermittently open hydrology of the lake probably with a tendency towards closure within certain intervals. The low correlation during 0.47–0.28 Ma suggests a hydrologically open lake, while the relatively high δ18O values suggest a longer residence time of the lake water. The high correlation (r = 0.92) of carbonate δ18O and δ13C from ~0.28 Ma to the last interglacial suggests a hydrologically-closed lake, although the Yellow River may have flowed through the Hetao Basin at that time. The interaction of the tectonically-controlled relative height of the basin spill point and the climatically-driven sediment and water supply of the Yellow River was responsible for the long-term evolution of the paleolake within the Hetao Basin. Strong regional tectonic activity which induced the uplift of the eastern part of the Hetao Basin and Jinshan Gorge and raised the relative height of the spill point was the primary cause of the formation of a hydrologically-closed lake within the basin.