Who opened the first page of the book of the Qinghai-Tibet Plateau’s stratigraphic structure?

What is the painting on the rock? It is like a book from heaven left in the world.

The strata of the Qinghai-Tibet Plateau are an endless book. It is a vast plateau with towering mountains, strong crustal movement, frequent changes between land and sea, and it only takes tens of millions of years to reclaim land. 80 million years ago, this inland plateau, now known as the "Roof of the World", was still an ocean, where various ancient creatures thrived and multiplied, leaving behind countless traces of life. These traces were buried under the sea, and turned into fossils in the long historical changes, engraved in the strata of the Qinghai-Tibet Seabed, and turned into a small fossil in the Himalayas along with the mountains and ridges created by crustal movement.

The magnificent Qinghai-Tibet Plateau contains countless paleontological resources among the mountains. Image source: Britannica

The Qinghai-Tibet Plateau is one of the regions with the most complete stratigraphic development in the world. Since ancient times, the plateau strata with a total thickness of nearly 40,000 meters accumulated over various periods are distributed among the towering mountains. The sedimentary records of paleontological relics are both complete and comprehensive, making it one of the rare regions for studying the global biological evolution history. However, due to the limitations of high altitude and lack of oxygen, scientific research in the Qinghai-Tibet Plateau is very difficult. Until the 1980s, the level of paleontological work on the Qinghai-Tibet Plateau was still very low, and research on large areas was still blank, and more systematic and detailed stratigraphic research was even rarer.

But the harsh environment did not shake the fighting spirit of Chinese paleontologists. In recent years, batches of scientific expeditions have gone to Qinghai-Tibet to conduct geological and paleontological surveys. They are under the snow of Tianshan Mountain and face the sandstorms of Gobi Desert. The documents of their predecessors in Tibet are their maps; the geological hammer in their hands is their weapon. With the efforts of generations, the early life page of the Qinghai-Tibet fossil book - the Ediacaran biota in the Quanjishan area, was finally opened by scholars from Nanjing Institute of Paleontology, Chinese Academy of Sciences.

All the way to the mountain, the lights are dim

In 1947, a stratum containing a large number of mollusk fossils was discovered at the top of the Proterozoic strata in the Ediacara Mountains in southern Australia. This fauna includes possible coelenterates, annelids, arthropods, and some mysterious creatures that have long been extinct, and was named the Ediacara Biota. They have a unique body shape, no mouth or intestine, a flat body, and cannot move. Their bodies are mostly disc-shaped, tubular, and leaf-shaped. These animals are the earliest complex multicellular organisms known to date, showing us the primitive appearance of life on Earth before the Cambrian explosion of life, which is of great significance for understanding early animal evolution and paleogeography.

Dickinsonia, the most representative animal of the Ediacaran biota. Image source: Wikipedia

After that, similar organisms and similar species were found in many areas around the world. In China, Li Siguang and Zhao Yazeng named the stratum equivalent to the Ediacaran period as early as 1924, and officially named it the "Dengying Formation" in 1963, dating back to the late Ediacaran period, 550 to 539 million years ago.

The "Dengying Formation" is named after the Dengying Gorge of the Yangtze River in Yichang County, Hubei Province. Since 2000, the Precambrian Research Group of the Nanjing Institute of Paleontology, Chinese Academy of Sciences, has been conducting long-term work in the Three Gorges area of ​​Hubei Province. During field geological surveys, scholars noticed that some farmers' roofs were covered with thin slates dug from the Ediacaran strata; after seeking the consent of the homeowners, they went up to the houses to study, and unexpectedly they made a discovery: a large number of trace fossils lying in the tiles, seemingly waiting for their arrival.

Dengying Gorge in Yichang, Hubei, has beautiful scenery. Image source: Suiyiwo

Later in 2011, Zhou Chuanming, Chen Zhe, Wang Wei and Guan Chengguo came here again. When they walked to a farmyard, they found that the farmer was replacing new tiles and the slates removed from the roof were placed on the ground. The scientists immediately became excited and began to investigate skillfully. The hard work paid off, and the slates preserved the fossils of Ediacarans; in the following years, they discovered more than 400 Ediacaran fossils in the area, including more than a dozen groups: typical Ediacaran fossils (Hiemalora, Pteridinium, Rangea and Charniodiscus, as well as some new species that have never been found anywhere else in the world, such as the hollow, tubular fossils made of stacked rings, the "Wuhe Tube", as well as the Yilingworm and the single fossil Paracharnia dengyingensis.

A typical Ediacaran organism, Yilingworm. Image source: Nature

Fossils of the worm Dendrobium. Image source: Reference [4]

The Dengying Formation is distributed in central Guizhou, eastern Yunnan, southern Shaanxi, and western Sichuan. After that, Chinese scientists went westwards, wandering in the dust. From Guizhou and western Sichuan, they went westwards to the vast Qinghai-Tibet Plateau, and the exploration of the Qinghai-Tibet Ediacaran Period also began.

The insect's name is Chani, the timing depends on you

In July 2020, the Early Life Research Team of Nanjing Institute of Paleontology, Chinese Academy of Sciences, cooperated with researchers from Peking University and Chengdu University of Technology to conduct an expedition to the Qinghai-Tibet Plateau. There were new faces in this expedition: Pang Ke, Ouyang Qing, Lang Xianguo and others, as well as old acquaintances such as Chen Zhe and Zhou Chuanming. They discovered typical**Ediacara fossils in the Quanjishan area on the northern edge of the Qaidam Plateau. **This is the second Ediacara fossil site discovered in China after the Three Gorges area in Hubei, and it is also the oldest fossil biota discovered on the Qinghai-Tibet Plateau so far.

The newly discovered Ediacaran fossils in the Wrinkled Mountains Formation are represented by Charnia. Charnia is a frond-like organism that grew fixed to the seafloor in the late Ediacaran period. It has a leaf-like appearance, no mouth, no digestive and motor systems, and is presumed to feed on free nutrients in the water. Although Charnia looks like a fern, it must be an animal, not a photosynthetic plant, because it was found in sediments in a deep water environment where no light can reach.

3D reconstruction of Charney. Image source: Free 3D

The discovery of Charnis is of great significance. It is the first recognized Precambrian complex macroscopic fossil and one of the most typical fossils of the Ediacaran biota. Therefore, its discovery means that Ediacaran organisms once lived in the Qaidam plate, and the age of the strata can be preliminarily determined based on the survival time of Charnis - about 574-540 million years ago.

Fossils of Chanis worms found in the Zhoujieshan Formation. Image source: Reference [7]

The name of the site is Shaanxi, and the location is determined by the stone

In addition, Shaanxilithes fossils, which are more abundant in number, have been found in the Zhoujieshan Formation, with more than 600 of them. Shaanxilithes are banded fossils with densely arranged horizontal stripes. The spacing between the "horizontal stripes" is usually 0.34 mm, the total length ranges from 2 to 3 cm, and the width ranges from 1 to 5 mm. The group and morphology of Shaanxilithes are not yet fully understood, but Chinese scientist Wang Xin, based on data from seven fossil sites and a large amount of fossil evidence, has restored its three-dimensional morphology to a "tube-in-tube" structure composed of an inner tube formed by a series of nested cup structures and a plastic (wrinkled) film-like outer tube, which has more reliably restored its living state.

The restoration of the Shaanxi traces in a sleeve shape should not restore the soft part but only reflect the hard shell.

Image source: Reference [6]

The original composition of its outer tube may be soft organic matter with a certain plasticity, which plays a role in wrapping and fixing the inner tube; the composition of the inner tube may be chitin with a slightly higher hardness, which plays a role in supporting and protecting the central cavity. At the same time, based on the research, Wang Xin proposed that the Shaanxi trace has a very high morphological similarity with the living deep-sea tubular worms, and tends to classify the Shaanxi trace into the annelid polychaete, which is an "Ediacaran tube worm" that lives in shallow sea environments and has the beginning of the tube body inserted into the muddy or sandy substrate to live a benthic life.

Shaanxi trace fossils discovered by researchers at Zhoujie Mountain. Image source: Reference [7]

Modern polychaete. Image source: YouTube

The Shaanxi trace was first reported in the Late Ediacaran Dengying Formation in Ningqiang area in southern Shaanxi, representing a stratum close to a normal marine environment; later, the Shaanxi trace was widely found in strata dating back 550 to 539 million years, including South China, North China, India, Siberia and Namibia, becoming a potential standard fossil for the division and comparison of Late Ediacaran strata.

The Book of Heaven has been cast, who dares to turn it over?

The co-occurrence of Chanis and Shaanxi traces in the Zhoujieshan Formation indicates that the age of this area is likely to be 550-539 million years ago, which is the same period as the Ediacaran Dengying Formation in Hubei Province. At the same time, scientists have found that the strata of the Zhoujieshan Formation are closely connected with the Hongtiegou Formation moraines, which indicate a cold and frozen climate. Moraines are rocks formed by direct accumulation of glaciers. Their appearance indicates that there were glaciers and cold climate activities in the Qaidam Basin at that time. Therefore, researchers speculate that the Qaidam Basin in the Ediacaran period may be located in the temperate or cold zone, rather than the tropical zone as has been generally believed.

Glacial till is rock formed by direct deposition of glaciers, or by glacial and glacial marine action.

Image source: AGU Blogosphere

In addition, scientists have discovered another subtle connection. The area of ​​the Zhoujie Mountain produced Shaanxi trace fossils, and the western and southern edges of the contemporary North China strata also produced Shaanxi trace fossils; coincidentally, the strata in these two places are composed of moraine and sandstone, indicating that the Qaidam Plate may have been located near the North China Plate at that time, estimating the geographical location of this plate of the Qinghai-Tibet Plateau in the Ediacaran period.

Thus, the cover page of the Qinghai-Tibet stratigraphic book was opened by a young Chinese paleontologist. Although in the future, with new explorations, this "cover page" may become the second or third page, it does not matter that this exploration has added a strong touch to the fossil record of early life in the Qinghai-Tibet stratigraphic book. This book, as well as the Qinghai-Tibet geology books compiled in the future, can add a sentence: "550 to 539 million years ago, in the Ediacaran period when multicellular organisms began to radiate, the Qaidam Plateau of the Qinghai-Tibet Plateau was located in the temperate and cold zone, a shallow sea close to the North China Plate."

References:

[1] Wei Zhensheng, Tan Yueyan. Overview of Tibetan Strata[J]. Geological Anthology of the Qinghai-Tibet Plateau, 1983(05):1-38.

[2] Hua Hong, Cai Yaoping, Min Xiao, Chai Shu, Dai Qiaokun. The “Great Radiation” of Tubular Animals at the End of the Ediacaran Period[J]. Journal of Northwest University (Natural Science Edition), 2020, 50(02): 141-174.

[3] Fang Ruisen, Liang Yue, Hua Hong, Zhang Zhifei. The first appearance of the difficult fossil Shaanxilithes from the late Ediacaran period in the Zhujiaqing section of Huize, Yunnan and its significance [J]. Acta Paleontologica Sinica, 2021, 60(01): 25-41.

[4] Liu Xusheng. The world's only lantern shadow chaenis insect[J]. Land and Resources Guide, 2012, 9(06):75-76.

[5] Ding Qixiu, Chen Yiyuan. Discovery of soft-bodied metazoan fossils from the Sinian Period in the eastern part of Hubei Province and its significance[J]. Earth Science, 1981(02):53-57+276.

[6]Wang X, Zhang X, Zhang Y, et al. New materials reveal Shaanxilithes as a Cloudina-like organism of the late Ediacaran[J]. Precambrian Research, 2021, 362: 106277.

[7]Pang K, Wu C, Sun Y, et al. New Ediacara-type fossils and late Ediacaran stratigraphy from the northern Qaidam Basin (China): Paleogeographic implications[J]. Geology, 2021.