What’s green that goes up and down?

The ups and downs of the Tibetan Plateau finally explained

What is green that goes up and down? No it is not a pea in an elevator but a palm on the plateau of Tibet. This was suggested by the data from previous studies, which up until now indicated that the plateau was high 35 million years ago, then low around 25 million and finally high since 15 million.A problem that induces a lot of cranial scraping and a multitude of models combining yoyo-like movements and a complex paleo-topography with valleys or peaks to satisfy these conflicting data. An article published in December 2020 in the journal Science Advances with Fang Xiaomin (Institute of Tibetan Plateau Research, Chinese Academy of Sciences) and Guillaume Dupont-Nivet (Potsdam University, Géosciences Rennes) solves these contradictions.

Why so many efforts to constrain the topography of the plateau of Tibet? Because it represents a lot. For geologists, his growth is indicative of the geodynamic regime that formed the largest mountainous expanse in the world. For climatologists, the plateau is the third pole responsible for Asian monsoons and perhaps the cause of the mysterious very long-term cooling that characterizes the planet’s climate before its current warming. For biologists, the plateau is a species pump and perhaps a refuge for the cold-acclimated fauna and flora that colonized the Arctic during the glaciations. In any case, it is a booming Eldorado because in the sediments screened on the plateau are exhumed in abundance of fossils and soils testifying to past environments (Oxygen and hydrogen isotopes of water preserved in soil and plant remains may indicate temperature and altitude at deposition).

This study now shows that these sediments were badly dated. Palm fossils that do not withstand the frost of high altitudes were supposed to be newer than soils with isotopic signatures of very high altitude (more than 4000 meters!). But it is the opposite that is shown today by researchers of the prestigious Plateau of Tibet Research Institute (ITPR) of the Chinese Academy of Sciences (CAS) in collaboration with the CNRS at Géosciences Rennes as part of the ERC MAGIC project led by Guillaume Dupont-Nivet. By combining different types of dating directly on the sedimentary layers that preserved these fossils and soils in the middle of the plateau, the result is implacable: the palms are 39 million years old and the soils are only 26 million years old. The plateau can thus quietly grow between these two ages. A little disappointing for lovers of yoyo and roller coaster? Not really because having low altitudes 39 million years ago does not fit too well with the collision of India with Asia which begins around 60-50 million and must be accompanied by intense overerction. The authors thus come to imagine an important topography of the proto-Himalayas in the south with a green valley in the north allowing a rich biodiversity, intense erosion and monsoons that finally reconcile field data with the results of ancient climate models.

Fang, X., Dupont-Nivet, G. et al., Revised chronology of central Tibet uplift (Lunpola Basin), Science Advances, 2020; 6 : eaba7298 DOI: 10.1126/sciadv.aba7298