Paleo‐altimetry of the Tibetan Plateau as indicated by mammalian fossils

on the earth, and its elevation reaches one-third of the height of the troposphere, with profound dynamic and thermal effects on atmospheric circulation and climate. The uplift of the Tibetan Plateau was an important factor of global climate change during the late Cenozoic and strongly influenced the development of the Asian monsoon system. However, there have been heated debates about the history and process of Tibetan Plateau uplift, especially the paleo-altimetry in different geological ages. The Lunpola Basin in northern Tibet has well-developed Cenozoic strata and an average elevation of about 4700 mm above sea level (asl). The total thickness of Cenozoic deposits in the Lunpola Basin is over 4000 m, and consists of the Niubao Formation in the lower part and the Dingqing Formation in the upper part. Estimations of the paleoelevation of the Lunpola Basin have been very different. During the deposition of the Dingqing Formation, the lowest estimate has been reported to be about 1000 m, but the highest published estimate is 4500 m. Recently, a humerus fragment of the Early Miocene rhino Plesiaceratherium was found in the Dingqing Formation, which was significant for age determination and the paleoaltimetry estimation. Plesiaceratherium has been inferred to live in subtropical and warm temperate forests, preferring a warm and humid climate. The correlations and adjustments based on modern alpine vegetation vertical zones in the Himalayas and the Early Miocene global climatic conditions indicate that the highest elevation in the Lunpola Basin at the time of the deposition of the Dingqing Formation could not have exceeded 3170 m asl. Thus, considering the ecological requirements of rhinos through a paleo-temperature adjustment for the Early Miocene, the most reasonable paleo-elevation for Plesiaceratherium is close to 3000 m asl. The material of the three-toed horse Hipparion xizangense from Bulong, Biru in northern Tibet includes limb bones, especially distal elements, with an age of early Late Miocene at about 10 Ma. The metapodial proportions of H. xizangense are nearly identical to those of H. primigenium from Europe, indicating their common locomotive function, which means that H. xizangense was a woodland-forest horse and lived in a habitat with a lower elevation. Combining with the rodent Brachyrhizomys naquensis and the palm pollens in the same horizon, the forest where H. xizangense lived in should be lower than an elevation of about 2500 m asl. Hipparion forstenae from the Gyirong Basin in southern Tibet is represented by skulls and mandibles, but lacking limb bones, with an age of late Late Miocene at 7.0 Ma. H. forstenae was widely distributed in Gansu and Shanxi provinces in eastern China with a lower elevation, so this species would have lived in similar environments in Gyirong. The presence of significant amounts of C4 grasses in the diets of H. forstenae and other herbivores from Gyirong indicates that the climate in the area was much warmer and the elevation was much lower in that time than today. The carbon isotope data from the high Himalayas, after accounting for late Cenozoic global cooling and paleoatmospheric CO2 levels, indicate that this part of southern Tibet was less than 2900~3400 m asl in the latest Miocene. A well-preserved skeleton of the Pliocene Hipparion zandaense was found from the Zanda Basin in southwestern Tibet, with an age of 4.6 Ma. Morphological features indicate that H. zandaense was a cursorial horse that lived in alpine steppe habitats. Because this open landscape would be situated above the timberline on the steep southern margin of the Tibetan Plateau, the elevation of the Zanda Basin at 4.6 Ma ago was estimated to be ~4000 m asl using an adjustment to the paleo-temperature in that time as well as comparison with modern vegetation vertical zones. Thus, we conclude that the southwestern Tibet Plateau achieved the present-day elevation in the mid-Pliocene. DENG Tao, 2013. Paleo-altimetry of the Tibetan Plateau as indicated by mammalian fossils. Acta Geologica Sinica (English Edition), 87 (supp.): 857-858.