Orbital Forcing of Climatic Changes on the Central Tibetan Plateau Reveals Late Oligocene to Early Miocene South Asian Monsoon Evolution

The uplift of the Tibetan Plateau (TP) is generally considered to have triggered the Asian monsoon system. However, a long-standing scarcity of high-resolution paleoclimatic records on the TP makes it unclear when the South Asian monsoon (SAM) reached the central TP. Here, we investigated the environmental magnetic properties of a lacustrine sequence (∼25.5–19.8 Ma) from the Lunpola Basin. Hematite is the dominant magnetic mineral with concentrations that vary with “box-shaped” peaks that mainly resulted from preferential preservation and dissolution of detrital iron oxides in alternating nonsteady state redox environments. Environmental magnetic sequences reflect distinct dry-wet cycles with a ∼400 kyr eccentricity periodicity, which are proposed to have been driven by SAM intensity. Therefore, our study reveals that the SAM intensified and advanced northward to the Lunpola Basin by at least ∼25.5 Ma.