The central part of the Qinghai-Tibet Plateau, which has an average altitude of 4600 meters or more, is now an alpine barren land.
Many details of the evolution of how the Qinghai-Tibet Plateau was raised to its current height are still unclear.
The Jianglang plant fossils recently discovered by my scientists refreshed people’s understanding of the Qinghai-Tibet Plateau——
The cold central Qinghai-Tibet Plateau was a subtropical forest 47 million years ago?
A few days ago, China and Nepal formally announced to the world that the latest elevation of Mount Everest is 88.886 meters.
The rise of Mount Everest and the adjacent Qinghai-Tibet Plateau did not happen overnight.
For a long time, the history of surface uplift of the Qinghai-Tibet Plateau has been the boundary condition of numerous geological and climatic environmental events since the Cenozoic, as well as a hot and difficult point in the study of the Qinghai-Tibet Plateau.
In the long process of ascending, there are a lot of puzzles: what exactly was the Qinghai-Tibet Plateau before it reached its current height?
In the "cold" Qinghai-Tibet Plateau, did a warm "Shangri-La" really hide tens of millions of years ago?
On December 7, the Proceedings of the National Academy of Sciences of the United States published for the first time an important "exploration" result of Chinese scientists on the central part of the Qinghai-Tibet Plateau 47 million years ago, which made up a large number of gaps in previous knowledge and research.
Discovery of the most abundant plant fossils in the Paleogene
The central part of the Qinghai-Tibet Plateau, with an average altitude of over 4,600 meters, is a vast alpine barren land, but it is a key area for understanding the formation process of the Qinghai-Tibet Plateau. It has long attracted attention from the fields of earth science and life science.
Despite decades of investigation, the details of the evolution of the Qinghai-Tibet Plateau are still unclear.
"Why study the Qinghai-Tibet Plateau? Because the formation of the Qinghai-Tibet Plateau is the most important geological event in the world in the Cenozoic Era. It has changed the topography of our Asia, and shaped the Asian monsoon climate and the current biodiversity distribution pattern." Chinese Academy of Sciences Researcher Su Tao from Xishuangbanna Tropical Botanical Garden said straightforwardly that the Qinghai-Tibet Plateau is a very important research area, not only for geology, biology and other disciplines. The time and method of plateau uplift that people are concerned about are also the study of the Tibetan Plateau. hot spot.
"As the youngest and highest mountain on earth, the Himalayas were formed by the collision of the Indian subcontinent and the Eurasian plate. However, there are still disputes about the history and mechanism of the uplift of the Himalayas." Researcher Che Jing, Kunming Institute of Zoology, Chinese Academy of Sciences Say.
At present, there are two main hypotheses about the history of the uplift of the Himalayas: one is the recent uplift hypothesis, which is supported by hydrological and thermal evidence, and it is believed that the Himalayas did not reach the current height until the mid-Pliocene; Progressive uplift hypothesis. This hypothesis believes that the Himalayas began to uplift in the late Paleocene, but the uplift was relatively slow in the early stage. It was not until the Miocene that the Himalayas began to uplift rapidly and reached the current height.
Fossils are the product of the co-evolution of organisms and the environment during a long geological period, and are the key evidence for discussing the evolution history of plateau biodiversity and the formation process of plateaus.
By studying fossils, scientists can understand the history of biodiversity in geological periods and the process of environmental changes.
In the past 10 years, Chinese scientists have discovered palm, climbing perch, water strider and other fossil groups through extensive field work on the Qinghai-Tibet Plateau. The types are very rich. These groups no longer exist in the central part of the Qinghai-Tibet Plateau.
Recently, the “Second Qinghai-Tibet Plateau Comprehensive Scientific Investigation and Research” paleontology expedition team jointly organized by the Palaeoecological Group of the Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences and the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences has united many domestic and foreign research institutes in In the wind and frost in the wilderness, under the strong plateau ultraviolet conditions, a lot of field work and related research have been carried out.
Hard work pays off.
Not long ago, the scientific expedition team made a major discovery in a set of gray mudstone when conducting scientific research at a location called Jiang Lang in the Bangor Basin of Nagqu City in the middle of the Qinghai-Tibet Plateau.
"Through our survey of the entire set of exposed strata, we found that there are 5 layers of fossil-producing layers, and the species are very rich. This is the most abundant Cenozoic fossil flora found on the plateau so far." Su Tao said, this The discovery means that the Paleogene Qinghai-Tibet Plateau has rich plant diversity that is completely different from today.
Have close communication with the flora of the northern hemisphere
The Jianglang flora discovered by Su Tao this time belongs to the Paleocene to Eocene Niubao Formation. It is located at the current 4850 meters above sea level in the "Bangong Lake-Nujiang suture zone" in the middle of the Qinghai-Tibet Plateau.
"In the multiple layers of this set of strata, we have discovered a large number of plant fossils, including leaves, fruits, seeds, flowers, underground tubers, etc., divided into more than 70 morphological types. This is by far the most species found on the Qinghai-Tibet Plateau. Abundant Cenozoic flora." Su Tao introduced to a reporter from Science and Technology Daily that the absolute geological age of the Jianglang flora is about 47 million years through uranium-lead radioisotope determination.
"Many plant species in the Jianglang flora are the earliest fossil records of the Qinghai-Tibet Plateau and even Asia, and they have a high similarity to the flora of the same period in the northern hemisphere." Researcher Zhou Zhekun from the Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences told reporters that this flora Many species, such as Lagocarpus, Ulmus, Ceratophyllum, Ailanthus, etc., are the earliest fossil records of these groups in the Qinghai-Tibet Plateau and even in Asia; some species, such as the Samara family, and even this group have been The earliest known fossil record in the world.
"The discovery of these fossil groups indicates that the Qinghai-Tibet Plateau is one of the important sources of plant diversity in the surrounding areas." Su Tao said that its biodiversity is important to the Qinghai-Tibet Plateau and surrounding areas, such as Southeast Asia, and even the entire Asia. The contribution is very large.
It is very interesting that there are many groups in the Jianglang flora that can be found in the Xishuangbanna Tropical Botanical Garden. Some seeds and fruits can correspond to ancient fossils.
"For example, there is a seed of the subfamily Asclepiaceae. At that time, we did not know its taxonomic location. There was a very accidental opportunity. On our way to work in the Xishuangbanna Botanical Garden, we actually found the seed corresponding to its present life. Match. This shows that more than 47 million years ago, the central part of the Qinghai-Tibet Plateau should have a tropical and subtropical climate type." Su Tao said.
Comparing with the flora of the same period, it is found that the Qinghai-Tibet Plateau has a similar flora composition with other parts of the Northern Hemisphere in the Middle Eocene, which means that the plant species have a high similarity.
Among them, the species resembling the Green River Biota in the United States is the highest, followed by the Messel Biota in Germany. For example, the genus Lagocarpa, Ailanthus, and Ulmus spp. appeared in the three flora at the same time, indicating that the Qinghai-Tibet Plateau and the Northern Hemisphere at that time There are close regional exchanges in other regions of China.
Paleoclimate reconstruction shows that it was once warm and humid
For a long time, people knew little about the topography of the Qinghai-Tibet Plateau and the complex relationship between the Asian monsoon and biodiversity.
In addition to paying attention to the ancient plants themselves, Su Tao and the others also focused on the environmental changes during the geological period of the Qinghai-Tibet Plateau. The "talking fossils" not only recorded the various components of the Qinghai-Tibet Plateau biota during the geological period, but also quantified the time. The climatic indicators such as temperature and rainfall provide the most direct evidence for the paleo-climatic features of the "Shangri-La" ecosystem hidden in the central Qinghai-Tibet Plateau more than 40 million years ago.
"Through the correlation between the morphological characteristics of the leaves and the climate, combined with the principles of thermodynamics, we quantitatively calculated the paleoenvironment of the central Qinghai-Tibet Plateau 47 million years ago: in the monsoon climate, the east-west central valley forest grew at an altitude of about 1,500 meters." Zhou Zhekun said that they used the climate-leaf multivariate analysis program to quantitatively reconstruct the paleoclimate of the fossil flora. The results showed that there was a warm and humid monsoon climate in the middle of the Qinghai-Tibet Plateau during the Miocene, and the area was both low and humid. The average temperature is about 19 degrees Celsius.
The team of Zhou Zhekun and Su Tao also used thermodynamic principles to reconstruct the ancient elevation of the flora, showing that there was an east-west central valley with an elevation of no more than 1,500 meters in the central part of the Qinghai-Tibet Plateau at that time. The north and south sides were the Gangdise Mountains and the Qiangtang Mountains. This is also supported by the model simulation results.
Combined with the palm fossil evidence published in the early days of the Paleoecological Group, the Central Valley, after more than 20 million years, due to northward compression and denudation and filling, did not gradually form the current plateau until the Miocene.
According to Su Tao, the structure of the Qinghai-Tibet Plateau itself is very complex. It is made up of different plates; and the history of the formation of different plates is different.
This valley and the ecosystem it occupies lasted until the Miocene epoch gradually ended.
"This research also provides an important paleontological basis for exploring the formation process of the plateau." Zhou Zhekun reminded that in the future, studying the evolution history of the biodiversity of the Qinghai-Tibet Plateau and the process of paleoenvironmental changes needs to consider the differences in the formation process of the Qinghai-Tibet Plateau. And complexity.
Our reporter Zhao Hanbin