The onset and dynamic processes of Central Asian aridification are pertinent to regional and global tectonic and climatic events. The Qaidam Basin, located in the northern Qinghai-Xizang Plateau, provides a key archive for understanding the evolutionary history of Central Asian aridification over the Cenozoic. However, paleovegetation and paleoclimate conditions in the basin during the early Oligocene remain poorly constrained. Here, we present an integrated study of the early Oligocene palynological and biomarker records from the macrofossil-bearing horizons at the Dahonggou section. The Random Forest algorithm and Coexistence Approach were used for reconstructions. Vegetation reconstruction indicates that temperate broadleaf deciduous forests generally dominated the regional vegetation within the basin. The paleoclimate reconstructions reveal that the Qaidam Basin was characterized by a temperate and wet climate with markedly weaker precipitation seasonality during the early Oligocene. These findings are corroborated by n-alkane indices, including average chain length, carbon preference index, and proportion of aquatic macrophyte-derived n-alkanes, which collectively reflect enhanced terrestrial inputs and a relatively deep paleolake. Together, these results demonstrate that the Qaidam Basin had not yet transitioned into its modern arid state by the early Oligocene, providing important evidence for the spatial and temporal heterogeneity of Central Asian aridification.
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