Carbon and oxygen isotopic constraints on paleoclimate and paleoelevation of the southwestern Qaidam basin,northern Tibetan Plateau

We investigate the growth of the northern Tibetan Plateau and associated climate change by applying oxygen and carbon isotopic compositions in Cenozoic strata in the southwestern Qaidam basin. The X-ray diffraction and isotopic studies reveal that the carbonate minerals are mainly authigenic and they do not preserve any evidence for detrital carbonate and diagenesis. The isotope data show large fluctuations in the δ¹⁸O and δ¹³C values in the middle–late Eocene, indicating relatively warm and seasonal dry climate. The positive correlation of the δ¹⁸O and δ¹³C values in the Oligocene and the positive shift of the δ¹³C values from the Eocene to Oligocene suggest that the climate changed to arid in the Oligocene. However, the δ¹⁸O values show negative shift, which is closely related to the global cooling event. During the Miocene, the δ¹³C values vary between –2‰ and –4‰, whereas the δ¹⁸O values show continuous negative shift. The mean δ¹⁸O values decrease from –8.5‰ in the early Miocene to –10.0‰ in the late Miocene. The stable isotope-based paleoaltimetry results suggest that the elevation of the southwestern Qaidam basin was approximately 1500 m in the middle–late Eocene and Oligocene. Subsequently, during Miocene the crustal uplift process started and the elevation reached approximately 2000 m in the early Miocene and 2500 m in the late Miocene, which suggests large-scale growth of the northern Tibet Plateau during the Miocene.