Pollen evidence for an Eocene to Miocene elevation of central southern Tibet predating the rise of the High Himalaya

Quantifying the elevation history of the 2000 km-wide Tibetan Plateau to an average elevation of 5 km is important for understanding key aspects of Cenozoic global climate change, collision tectonics and the evolution of the Asian monsoon, yet quantitative measures of Cenozoic surface height change across Tibet remain few and are sometimes contradictory. Here we report the first exploratory application of a modified Co-existence Approach (CoA) using previously published fossil pollen records to reconstruct quantitatively the Cenozoic minimum palaeoaltitudes of Gangdise-Nyainqentanglha Area of the Tibetan Plateau. GCM simulations were used to adjust Eocene and Miocene raw CoA values for secular climate change and changes in palaeolatitude. This modelled correction increased the CoA-derived altitudes by 895 ± 96 m to give a minimum overall Eocene altitude of 3295-3495 m. The Miocene correction factor of 481 ± 25 m gave an overall minimum altitude estimate of 3000-3150 m. For the Holocene CoA returns four equally likely elevations of 4800-4950 m, 3800-3900 m, 3000-3100 m and 2900-3000 m. The first of these is indistinguishable from the present day regional average while the others suggest significant upslope pollen transport. Both the Eocene and Miocene palynologically-derived height estimates are consistent with suggestions of significant core plateau elevation by the Eocene, but are likely to underestimate the true palaeoelevation due to pre-Himalayan upslope pollen transport.