Chinanews.com, Beijing, December 25 (Reporter Sun Zifa) about 23 million to 2.58 million years ago in the geological era of the Neogene (the second epoch of the Cenozoic Era, including the Miocene and the Pliocene), its general appearance of the biological world is closer to the modern era, which is not only one of the few epochs in the history of the earth that has had large-scale glacial activity, but also a geological era with a high degree of development of mammals and angiosperms, and the emergence of human beings is the most prominent event in the Neogene.
Since the significant uplift of the Tibetan Plateau in the Neogene has a great impact on the climate and environment of East Asia and even the world, the establishment of the Neogene stratigraphic framework of the Tibetan Plateau is of great significance to the research of various fields of earth science, and the academic community has been paying attention to and carrying out research for a long time.
Ecological restoration of the Pliocene mammal fauna in the Zada Basin, Tibet (Julie Selan/photo). Institute of Paleospine, Chinese Academy of Sciences/Courtesy photo
The team of researcher Deng Tao from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and the team of academician Fang Xiaomin from the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences have studied and summarized the Neogene strata and fossil groups in the Qinghai-Tibet Plateau and its surroundings, established and improved the Neogene high-precision comprehensive stratigraphic framework of the Qinghai-Tibet Plateau that can be used for international comparison, and identified the evolution characteristics of the Neogene paleoclimate environment in the Qinghai-Tibet Plateau and its surrounding areas.
This important paper on the paleoenvironment of the Qinghai-Tibet Plateau was recently published in the professional academic journal Science China: Earth Sciences with the title of "Neogene Comprehensive Stratigraphy, Biota and Paleogeographic Evolution of the Qinghai-Tibet Plateau and its Surrounding Areas".
Abundant mammalian fossils have been found in the Cenozoic basin of the Qinghai-Tibet Plateau
Researcher Deng Tao, the first author and corresponding author of the paper, said in an interview with reporters on December 25 that the international Neogene chronostratigraphic system is divided into 6 orders of the Middle Eocene and 2 orders of the Upper Eocene based on the marine phase. Since the Cenozoic, the proportion of terrestrial strata has increased rapidly, and by the Neogene it has far exceeded that of marine strata, and almost all of them are terrestrial strata in the Qinghai-Tibet Plateau and its surrounding areas. China's Miocene includes five stages: Xiejia Order, Shanwang Order, Tonggul Stage, Bahe Stage, and Baode Order, and the Upper Pliocene includes two stages: Gaozhuang Order, and Mazegou Order.
On December 25, Deng Tao, the first author and corresponding author of the paper and a researcher at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, was interviewed to interpret the research results in popular science. Photo by Chinanews reporter Sun Zifa
The stratigraphic sections of the Neogene Xiejia and Bahe formations are located in the Xining Basin and the Linxia Basin, respectively, and there are fine paleomagnetic dating and mammalian fossils, and the bottom boundaries of the other stages can also be effectively determined in the Qinghai-Tibet Plateau.
Mammals originated in the Mesozoic Era, and after entering the Cenozoic, mammalian fossils played a very important role in the division and comparison of terrestrial strata, especially rodents, carnivores, proboscis, odd ungulates and artiodactyls in the Neogene. Abundant mammal fossils have been found in a series of Cenozoic basins of the Qinghai-Tibet Plateau, such as the Bulong, Jilong, and Zada basins in Tibet, the Qaidam basin in Qinghai, the Linxia basin in Gansu, and the Xivalik area on the southern edge of the Tibetan Plateau. The biggest difference between mammalian fossils and other fossils, and the most advantageous, is that they evolve quickly, and their morphological characteristics are distinct and easy to identify.
Late Miocene Woma Formation stratigraphy in Jilong Basin, Tibet. Institute of Paleospine, Chinese Academy of Sciences/Courtesy photo
Deng Tao pointed out that even when fossils are few or even incomplete, paleomammals can easily chronologically rank fossils according to their evolutionary stage in the initial stage when fossil-bearing strata have not yet been studied in detail. Many mammalian genera in East Asia were first found in the Qinghai-Tibet Plateau and its surrounding areas, especially in the Linxia Basin on the northeast margin and the West Walik region on the southwest edge, among which the protophobia of Sivalik first appeared at the bottom of the Miocene (23 million years ago), and the earliest three-toed horse in Eurasia first appeared at the bottom of the Bahe Terrace in the Linxia Basin (11.6 million years ago).
The Cenozoic basin of the Qinghai-Tibet Plateau is divided into five stratigraphic zones
Deng Tao said that at the beginning of the Cenozoic, the Qinghai-Tibet Plateau fully completed the transformation of the Tethys ocean-land and the integration of the land mass, becoming a unified land mass and entering the stage of intracontinental evolution. In this study, according to the tectonic evolution background and formation mechanism, tectonic-geomorphological landscape, sedimentary filling sequence and sedimentary environment evolution process, the research team divided the Cenozoic basin of the Qinghai-Tibet Plateau and its surrounding areas into five stratigraphic areas, namely Nanjiang-West Kunlun District, Qaidam-Qilian-West Qinling Area, Qiangtang District, Western Yunnan-Western Sichuan Region, and Gangdis-Himalaya-West Walik Area, which can be further subdivided into sub-stratigraphic areas.
Comparison of Neogene strata on the Tibetan Plateau and its adjacent areas. Institute of Paleospine, Chinese Academy of Sciences/Courtesy photo
Subsequently, the research team analyzed the Cenozoic sediments and mammalian fossils contained in the Qinghai-Tibet Plateau and its surrounding areas, analyzed the enamel and paleosoil carbon and oxygen isotopes, and reconstructed the climatic and environmental background and vegetation development characteristics, which were related to global changes and regional characteristics.
The evidence of the Late Miocene C4 plant expansion event based on carbon isotope changes comes from the southern margin of the Tibetan Plateau, but in contrast, the carbon isotope values of multiple herbivorous mammal groups and paleosoil carbonates and organic matter indicate that there is still a lack of clear or significant C4 plant signals in the northern margin of the Tibetan Plateau until the end of the Neogene. Oxygen isotope analysis showed that there were several major climate change events in the Cenozoic, especially at the end of the Late Miocene, about 7 million years ago, and the north and south sides of the Tibetan Plateau transitioned to a drier environment.
The strong uplift of the Tibetan Plateau in the Late Miocene strengthened the thermal contrast between land and sea, which strengthened the monsoon circulation and led to the expansion of C4 vegetation in South Asia, but the East Asian summer monsoon that can bring atmospheric precipitation and a suitable climate for C4 plants to northern China is not enough to affect the northern part of the Tibetan Plateau. "The Tibetan Plateau as a whole rose to an altitude of about 3,000 meters in the Miocene about 20 million years ago, becoming a barrier to the communication of large mammals, and reached a modern altitude of more than 4,000 meters in the Pliocene about 5 million years ago, which formed a cryosphere environment, leading to the emergence of glacial fauna ancestral types. Deng Tao said.
Trends of stable isotopes of carbon and oxygen in the southern Tibetan Plateau in the Neogene. Institute of Paleospine, Chinese Academy of Sciences/Courtesy photo
It is reported that as one of the important evidences to prove the uplift process and amplitude of the Qinghai-Tibet Plateau, the three-toed horse fossil was found in the Miocene strata of the Woma Basin of Jilong County, Tibet and the Bulong Basin of Ruxian County in the first comprehensive scientific investigation of the Qinghai-Tibet Plateau in the 70s of the 20th century. In the 21st century, Chinese scientists have discovered fossils of the ancestral types of woolly rhinoceros, snow leopards, arctic foxes, and argalis in the Pliocene strata of the Zada Basin in Tibet's Ali region, and based on this, they have put forward the theory that the Quaternary glacial animals originated from the Qinghai-Tibet Plateau. (ENDS)