Paleomagnetic data points, magnetic susceptibility, colour reflectance and elemental data from a sediment outcrop of the Ashigong Formation near the Guide city in the northern Tibetan Plateau, China

Lake expansion displayed cyclic variations following ~100 kyr cycles and weaker ~41 kyr cycles, reaching its maximum between ~11.4 and 10.5 Ma. Our results show that the Guide Basin was hydrologically closed from most of the middle Miocene, confirming previous studies that proposed an early Miocene partitioning of this basin. The maximum lake expansion between 11.4 to 10.5 Ma is coeval to a known peak of monsoonal intensity.

This, and the evidence for a strong orbital control on lake expansion, supports a strong monsoonal control on the expansion of middle Miocene Tibet paleolakes. The origin of the ~100 kyr forcing on monsoonal moisture supply -different from Quaternary forcing— questions the climatic mechanism of these Middle Miocene monsoons and suggests that westerly-derived moisture might have also significantly contributed to the regional hydrological budget.