Thick Miocene lacustrine deposits have been identified across the Qaidam Basin on the northeast Tibetan Plateau, indicative of a relatively unified megalake then. How this megalake evolved at its final stage and associated controlling factors, e.g., global climate or tectonic uplift, remain largely elusive. Here we use the KC-1 well, drilled at the depo-center of the western Qaidam Basin, to investigate the megalake evolution over the mid- and late Miocene. A set of lipid biomarker indices, namely β-carotane/n-C₃₆, gammacerane index, terrigenous/aquatic ratio and long-chain saturated ketone content, altogether indicate substantial lake level fluctuations, with lower lake level at the intervals of ~18–17 Ma, 13.5–11.5 Ma, 10.5–8 Ma and 7–6 Ma, and higher level at the intervals of ~17–13.5 Ma, 11.5–10.5 Ma, 8–7 Ma and 6–5 Ma, superimposed on the long-term shrinking trend. Direct comparison with existing regional and global temperature records suggests that such lake dynamics was largely associated with global climatic conditions, i.e., shrinking under relatively cool conditions and vice versa, for both its long-term evolution and secondary fluctuations. It thus appears that global climatic conditions had controlled the megalake status during the mid- and late Miocene, whereas tectonic activities then might have also contributed to its long-term gradual demise.

在青藏高原东北部的柴达木盆地中发现了较厚的中新世湖相沉积物，这表明当时有一个相对统一的巨湖。这个大湖如何在其最后阶段演变以及相关的控制因素（例如全球气候或构造隆升）仍然难以捉摸。在这里，我们使用在柴达木盆地西部沉积中心钻探的KC-1井，来研究中新世中晚期的巨湖演化。一组脂质生物标志物指数，即β-胡萝卜素/ n -C ₃₆，γ-角鲨烷指数，陆源/水生比率和长链饱和酮含量一共表明湖水位有较大波动，而湖水位较低的时间间隔为〜18–17 Ma，13.5–11.5 Ma，10.5–8 Ma和7–6 Ma，以及更高的水平，其间隔为〜17-13.5 Ma，11.5-10.5 Ma，8-7 Ma和6-5 Ma，这与长期收缩趋势相叠加。与现有的区域和全球温度记录的直接比较表明，这种湖泊的动力学在很大程度上与全球气候条件有关，即，在其长期演化和次生波动方面，在相对凉爽的条件下不断缩小，反之亦然。因此，在中新世中期和晚期，全球气候条件似乎已经控制了巨湖状态，