The research team conducted a multidisciplinary joint expedition in the field. Courtesy of respondents
Representative spore pollen fossils of the Late Triassic in Xuanhan region, Sichuan. Courtesy of respondents
About 200 million years ago, a very important evolutionary event occurred on Earth. The originally connected Europe-North America-South America-Africa united paleonttomy disintegrated, and the Atlantic Ocean cracked in the middle. In the midst of the gushing sea, a volcanic group stretching for hundreds of kilometers emerged, they erupted day and night, thick smoke and volcanic ash covered the sky, and the end-Triassic mass extinction event in geological history began...
200 million years ago in Xuanhan, Sichuan, a large number of fern spores and gymnosperm pollen were blown away by the wind, drifted into the river, gathered together by water currents, and then "banned" by sand. After a long period of time, these spore pollens were buried deep in the formation and preserved as fossils. Today, 200 million years later, they are back in the light of day, and the codes left to us by these ancient worlds are being cracked by scientists one by one.
Recently, the international geological academic journal "Paleogeography Paleoclimate Paleoecology" published an important research result: Dr. Li Liqin and Wang Yongdong, researchers of the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences, cooperated with foreign counterparts to find rich spore pollen fossils in the section of Xuanhan Qili Gorge on the northeast edge of the Sichuan Basin, exploring the mysteries of ancient vegetation and climate evolution.
Since 2007, Wang Yongdong led the mesozoic plant and environmental research team of the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences, and cooperated with the then Suining Municipal Land Bureau of Sichuan Province, the Land Bureau of Shehong County, the 137 Geological Team of the Sichuan Coalfield Geology Bureau, Qufu Normal University, the Chemical Exploration Team of the Sichuan Provincial Geological Survey Bureau, the China University of Geosciences (Wuhan), Chengdu University of Technology and Sichuan University to carry out multidisciplinary in-depth research on the Triassic-Jurassic strata of the Sichuan Basin, and found plant leaves in many places in the Sichuan Basin. Spore pollen and rhizome fossils are consistent with the results of multiple cross-sectional studies around the world that are unraveling the mystery of paleograve succession and paleoclimate change at the turn of the Triassic-Jurassic period.
Small fossils of spore pollen open a door to us to explore the Sichuan Basin in ancient times.
The Sichuan Basin 200 million years ago
It is the "country of heaven" where grass and trees flourish.
At that time, the Sichuan Basin had a humid climate and lush vegetation, and tall gymnosperms and low ferns bred a huge family here - "It was precisely because of the diversity of land plants in the Sichuan Basin at that time that we could find a large number of fossils here."
Between 250 million and 201 million years ago, the Earth was in the Triassic period, the first epoch of the Mesozoic Era. At this time, the East Asian continent was not connected to the European continent, and they were separated by the vast Tethys Ocean. After the Haixi Movement, many troughs were converted into mountain systems, the land area expanded, and some inland basins were produced in the platform area. The Sichuan Basin and the Junggar Basin are typical examples of that period.
Li Liqin and other studies found that in the Sichuan Basin at that time, the climate was humid, the water and soil were fertile, the grass and trees were luxuriant, and tall gymnosperms and low ferns bred a huge family here, such as new reeds, double fan ferns, cycads, cycads, cycads, etc., as well as some mosses and stone pine plants also appeared in the forest.
Ferns, also known as sheep tooth plants, belong to spore plants, common ferns are mostly low in appearance, while ginkgo biloba, conifers, cycads and other hydrangeas are perennial woody plants, mostly tall trees, the two have different environmental requirements. The conifers in gymnosperms are mainly distributed in temperate and cold zones, cycads belong to tropical and subtropical plants, and ginkgo biloba plants prefer subtropical and cool environments. Most ferns prefer warm, moist environments, while a few are drought tolerant.
After hundreds of millions of years of geological movement, tall gymnosperms were buried hundreds or even thousands of meters underground, eventually forming coal. The low ferns are more tenacious and more tolerant of extreme environments, and some of them have survived to the present, such as the alder, known as the "living fossil" of plants, which have been found in Luzhou, Yibin, Leshan and other places in Sichuan, which also proves the richness of species in the Sichuan Basin from another side.
"It was precisely because of the diversity of land plants in the Sichuan Basin at that time that we were able to find a large number of fossils here, providing conditions for further research." Li Liqin speculated that Sichuan Xuanhan, Guangyuan, Hechuan and other places at that time the rivers, shoals and peat swamps were dense, and the periodic water rising and falling tides made the spores and pollen of many plants fall in the water and pool together, because the spores and pollen were very small, and the outer wall was hard enough, plus the water flow washed them together, it was easy to be buried and preserved by the underwater sand.
Similar to archaeology, spore pollen fossils of different geological ages are deposited in different strata, and scientists can judge the geological age, sedimentary conditions and earth's ecological environment at that time by studying the combined appearance of spore pollen fossils.
Pollen fossils decode subtle changes in the environment of the Sichuan Basin
The fossil spore pollen found in the Sichuan Basin has become a "decoder" to reveal the ancient environment - the Sichuan Basin also has a relatively warm and cool stage under the overall warm climate
Scientists believe that the Triassic mass extinction, one of the five major extinction events of the Ezoogene, occurred at the turn of the Triassic-Jurassic period, and the global marine and terrestrial ecosystems were severely damaged. Compared with the ocean, the exploration of major biological events at the turn of the Triassic-Jurassic of terrestrial ecosystems is relatively weak. The important reason is that the marine strata are more continuous and complete than the continental strata, and the storage conditions of plant fossils are more demanding, and it is difficult for scientists to restore the changes in the terrestrial ecological environment at that time only through large plant fossils.
Fossil spore pollen found in the Sichuan Basin has filled this gap and become a "decoder" to demystify the ancient environment.
Plant fossils are generally divided into three categories: leaf fossils, rhizome fossils, and spore pollen fossils. The first two are easy to spot but not easy to preserve, especially plant rhizomes, many of which turn into coal. However, spore pollen is easier to preserve because of its small size and hard outer wall and acid and alkali resistance.
These spores and pollen are less than 100 microns large and only about 30 microns, and must be seen clearly with the help of a microscope of 400 times, and can be clearly imaged after 600 times magnification. Scientists sometimes have to rely on a little luck to find them. Li Liqin said that this time they selected many coal-bearing formations on the northeast edge of the Sichuan Basin, circled the approximate range according to the lithology and other characteristics of the surrounding rocks, and then collected a large number of rock samples, and then went to the laboratory acid treatment and microscope observation and research. Eventually, a large number of pollen spore fossils were found in a large pile of inconspicuous stones.
"We noticed that although the environment in the Sichuan Basin, about 200 million years old, was generally warm and humid, the pollen types and relative content of ferns and ferns fluctuated greatly in different strata." Wang Yongdong explained that this shows that there are subtle changes in the climate environment, and under the overall warm climate, there are also relatively warm and cool stages.
After further detailed geological investigation and fossil specimen analysis, they concluded a law: in the Late Triassic, euthanasian ferns were absolutely dominant and represented by the double fan fern family, conifers and cycads, ginkgo biloba plants flourished, and a small number of seed ferns, stone pines, mosses and wedge leaf plants. At the end of the Late Triassic, conifers and cycads and ginkgo biloba plants predominated, and the palm scales of conifers began to appear, and there were fewer ferns. By the Triassic-Jurassic transition, plant diversity was low, with only a few ferns predominating. After entering the Early Jurassic Period, cycads and ginkgo biloba resurged, and the coniferous palm scale family was abundant, and the ferns were represented by the quercus/mussel shell fern family.
Volcanic activity may have contributed to changes in climate fluctuations in ancient times
The earth's climate change is cyclical and regular, and human beings are also experiencing the greenhouse effect, and finding these laws of evolution can help us find ways to actively cope with climate change
"In the past, many people believed that at the end of the Triassic Period, the Earth began to have a greenhouse environment, which led to the extinction of a large number of animals and plants. Our study more accurately analyzed climate change in the 6 million years before the mass extinction and found that the region experienced curve fluctuations of warm humidity (short-term cooling)-dry cooling-temperature recovery. Wang Yongdong told reporters.
Wang Yongdong introduced: "At the end of the Triassic Period, there were large areas of volcanic concentrated eruptions on the European continent and the African continent on the west coast of the Tethys Ocean, which were shrouded in volcanic ash that covered the sky, and a large amount of sulfur dioxide entered the sea, causing seawater acidification and hypoxia, 76% of marine life species became extinct, the sun was blocked by soot and volcanic ash, resulting in a rapid drop in temperature, and then due to the continuous accumulation of carbon dioxide emitted by volcanoes in the atmosphere, the temperature rose rapidly in a short period of time. ”
Although the Sichuan Basin is on the eastern shore of the Tethys Ocean, scientists previously believed that it was little affected by volcanic activity. However, with the refinement of geological records and the improvement of testing methods, scientists have found "clues" in many areas of the Sichuan Basin affected by volcanic activity, and believe that the volcanic ash drifting from the western edge of the Tethys Ocean gradually scattered here may lead to climate changes and fluctuations in these areas, which in turn will affect the terrestrial ecosystems and their environments, as well as the diversity of biota.
Wang Yongdong said: "The paleoclimate climate change trends of triassic-Jurassic transitional three-slit spores peaks, short-term cooling at the end of the Late Triassic and early Jurassic warming found in the Xuanhan region of Sichuan Province coincide with the research results of many representative profiles around the world, especially in the western edge of the Tethys Ocean, revealing global terrestrial paleoclimate and paleoclimate successional changes at the turn of the Triassic-Jurassic period." ”
This study is the most informative high-resolution record of spore pollen flora in southern China. "Understanding the characteristics of paleoclimate evolution helps us understand the laws of earth's climate evolution." Wang Yongdong said that the earth's climate change is cyclical and regular, such as the dinosaur era of the earth experienced a greenhouse effect caused by large-scale volcanic eruptions. At present, human beings are also experiencing the greenhouse effect, and finding out these laws of evolution can help us better understand the earth and find ways to actively cope with climate change.
unscramble
Pollen fossils "say" something
Late Triassic
True ferns are absolutely dominant and represented by the double fan fern family, conifers and cycads, ginkgo biloba plants flourish, as well as a small number of seed ferns, stone pines, bryophytes and wedge leaf plants.
Late Triassic end
Conifers and cycads and ginkgo biloba predominate, and coniferous palmis began to appear, with fewer ferns.
Triassic-Jurassic transition
Plant diversity is low, with only a few ferns predominating.
Early Jurassic
Cycads and ginkgo biloba are revived, and the coniferous palm scale family is abundant, and the ferns are represented by the quercus family/mussel shell fern family.
issue
How do I save it?
Spores and pollen are well preserved because they are so small and the outer walls are hard enough that they are easily buried and preserved by underwater sand. How to draw conclusions?
These spores and pollen are less than 100 microns large and only about 30 microns, and must be seen clearly with the help of a microscope of 400 times, and can be clearly imaged after 600 times magnification. Through imaging, it is found that the number and species in different strata fluctuate sharply, indicating that the two have a dominant position at different times, thus judging climate change.
Press background
Five mass extinction events
Scientists generally agree that there are five mass extinction events in the geological record. The chronological order of occurrence is as follows:
Ordovician mass extinction
The mass extinction occurred between 443.1 million years ago and 200,000 years ago, 442.9 million years ago. This period formed a large ice sheet with a total size of 150 million cubic kilometers, which is more than 6 times the size of the Earth's Antarctic and Arctic ice sheets combined today. At that time, the global sea level dropped sharply by 100 meters to 150 meters, and most marine life suffered a "catastrophe", and about 56% of species went extinct.
Late Devonian mass extinction
Occurring 372 million years ago, it wiped out about 70% of invertebrates. Fossil spores that existed for thousands of years during the Transition period of the Devonian and Carboniferous Periods show signs of ultraviolet destruction. Scientists suggest that the ultraviolet explosion could be caused by a supernova that exploded within 65 light-years of Earth.
Permian mass extinction
It occurred 252 million years ago, the worst of five mass extinction events, causing 98% of marine life and 96% of terrestrial life to disappear within 500,000 years, and a large number of organisms "evaporated" to the ground. Some scientists believe that the catastrophe was caused by the eruption of the Mount Emei supervolcano and the supervolcan eruption of Siberia.
Triassic mass extinction
Occurred 201 million years ago, an estimated 76% of species disappeared. This event was the dawn of the age of the dinosaurs, when early masterosaurs, most zygoteans, and large amphibians went extinct, allowing dinosaurs to take over the terrestrial world with little competition from land. Scientists speculate that the mid-Atlantic supervolcano eruption was responsible for the extinction event.
Cretaceous mass extinction
The most famous one occurred 66 million years ago, when the event led to the extinction of about three-quarters of all plant and animal species on Earth. On land, non-avian dinosaurs were all extinct. The extinction of these animals made room for the development of mammals, and the history of the earth entered the age of mammals. Experts believe that the mass extinction was caused by a huge asteroid or comet hitting The Earth, an impact that nearly wiped out the global environment. (Sichuan Daily all-media reporter Kou Minfang)
(Editor-in-charge: Li Qiangqiang, Gao Hongxia)