Fang Xiaomin, a researcher from the Qinghai Tibet Plateau Institute of the Chinese Academy of Sciences, led several members of the Cenozoic environmental team, and cooperated with many scholars at home and abroad, such as Miao Yunfa, a researcher from the Northwest Academy of the Chinese Academy of Sciences, to tackle key problems. Using 3088 representative layer pollen sample databases, a new method for retrieving ancient altitude was established from the perspective of biological indicators, and was applied to the research of late Cenozoic strata pollen in the Qaidam Basin, The ancient altitude evolution history of the northeastern Qinghai Tibet Plateau has been reconstructed, revealing that the area was mainly uplifted about 11 million to 7 million years ago, and had a strong environmental effect. Relevant achievements were published in Science on December 9.
The uplift of the Qinghai Tibet Plateau led to surface deformation and the formation of large landforms, driving the evolution of Asian monsoon arid climate and alpine biodiversity. However, the existing methods for quantitatively reconstructing the ancient height of the plateau surface often draw different conclusions, resulting in many disputes.
"How the plateau surface rises is crucial for examining the dynamic model of the plateau uplift, understanding a series of major scientific issues such as the formation of the monsoon arid environment pattern, the formation and evolution of Asian topography and rivers, weathering and denudation, and global change. At present, no unified conclusion has been reached, and the study of the ancient height in the northeast of the plateau is relatively weak." The co correspondent author of this article, Fang Xiaomin said, "Looking for an effective method, which is different from the existing two quantitative reconstruction methods based on isotope and leaf facies analysis, can provide important independent discrimination evidence for resolving the history of ancient height disputes in many regions."
Fang Xiaomin et al. started with the mountain coniferous groups closely related to altitude, and found that hemlock, tamarisk, fir and spruce, which are suitable for growing at middle and low altitude in mountain areas, and which prefer middle and high altitude, can be used as good altitude indicators. After scientifically eliminating the influence of latitude effect, the research team innovatively constructed a new index of plant spore and pollen to quantitatively depict the past altitude, established a modern altitude calculation equation, and verified its accuracy with spore and pollen records in the Qinghai Tibet Plateau since the Quaternary.
The research team used the spore pollen data of four chronologically accurate sections and boreholes in the Qaidam Basin in the northeast of the Qinghai Tibet Plateau, combined with the plant fossils found on the sections, and used the altitude formula established above to obtain the continuous records of the ancient height changes of the mountains on both sides of the eastern and western sections of the Qaidam Basin for 16 million years after correction, revealing that the eastern and western parts of the Qaidam Basin were about 15 million years ago The ancient elevations in the west were 1332 ± 189 meters and 433 ± 189 meters respectively. Later, the eastern section rapidly rose to 3685 ± 87 meters about 11 million years ago, and the western section rapidly increased to 3589 ± 62 meters about 7 million years ago, approaching the modern height.
"Our research shows that the northeast of the Qinghai Tibet Plateau was strongly uplifted in the late Cenozoic, about 11-7 million years ago. This uplift should not be underestimated, and it has had a very important impact on the regional climate environment and ecological evolution." Fang Xiaomin said.
By running the high-resolution regional climate model RegCM4.6, the research team also found that if the altitude of the northeastern Qinghai Tibet Plateau decreases by 2/3, the annual precipitation of the northeastern Qinghai Tibet Plateau will decrease by more than 50%; The precipitation in the Himalayas and Hengduan Mountains in the south and southeast of the plateau increased by 50% and 150% respectively. Through analysis, it is found that the main reason is the enhancement of mountain rain shadow effect and the joint influence of regional circulation changes. This understanding is consistent with the gradual increase of desert plant groups and the occurrence of calcified coarse skeleton fish in the western Qaidam Basin; In the Himalayas and Hengduan Mountains, the significant increase in precipitation has enhanced the diversity of local vegetation and reptiles, indicating that the precipitation change caused by the uplift of the northeastern Qinghai Tibet Plateau has affected the climate and biological evolution of the entire Qinghai Tibet Plateau region.
The above research has created a new method to reconstruct the ancient height from the aspect of biological indicators. Because the pollen of the above four conifers is widely distributed in the late Cenozoic strata, well preserved, easy to identify, and can obtain a continuous historical record of the ancient height, it is better than the paleosoil calcium nodule isotope altimeter accidentally found in the strata and the leaf facies altimeter of plant fossils in terms of use conditions.
The reviewers of this paper agreed that this method provides an important new way to more systematically and deeply reveal the ancient height history of the Qinghai Tibet Plateau, deepen the understanding of the Cenozoic orogeny and its resulting climate and biodiversity evolution, and is conducive to promoting the progress of the discipline.
Relevant paper information: https://doi.org/10.1126/science.abo2475
