Direct dating of Qaidam Basin stratigraphy, Northern Tibet

• Calcite U-Pb dating indicates that the initial terrestrial deposition of Lulehe Fm in the Qaidam Basin begin in the Early Eocene. • The Early Eocene paleoelevation of the Qaidam Basin is estimated at 1600±980 m, addressing a key gap in prior history. • The potential for southward growth of the Northern Tibet during the Eocene remains a viable hypothesis. The Qaidam Basin, the largest intermountain basin in Northern Tibet, has recently gained attention for a newly proposed depositional age, specifically for the Lulehe Formation (Fm). Two contrasting models currently exist: the traditional interpretation places its deposition during the Paleocene or Eocene, while more recent age models suggest deposition during the Oligocene. This significant conflict hampers understanding of the timing of activity of the surrounding fault systems, and the uplift and growth mechanism of the northern Tibet. In this study, we sampled tubular carbonate veins and abundant paleosol calcareous nodules from the Lulehe Fm. Using calcite U-Pb dating and clumped isotopes, we obtained an average age of 50.8 ± 2.8 Ma and formational temperatures of the nodules ranging from 39.6 ± 2.3 °C to 43.2 ± 3.4 °C in the Honggou section, and 28.2 ± 0.7 °C to 34.3 ± 4.2 °C in the Hongshan West section. Furthermore, by applying elevation-dependent isotopic and clumped temperature lapse rates, we reconstructed the paleoelevation of the Qaidam Basin during the early Eocene to be 1.6 ± 0.98 km. Our findings align more closely with the traditional stratigraphic framework of the Lulehe Fm, indicating that initial sedimentation in the Qaidam Basin occurred during the early Eocene. Moreover, we provide a quantitative estimate of the basin's paleoelevation during its early stage. While our data may suggest the possibility of southward growth in northern Tibet, alternative interpretations cannot be ruled out, and further research is required to better constrain the uplift patterns.