Source: China News Network
BEIJING, July 28 (Xinhua) -- What was China's Yangtze River Basin like 438 million years ago? The latest research by the early vertebrate research team of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (Institute of Paleovertebrates of the Chinese Academy of Sciences) gives an answer to the "vicissitudes of the sea": through in-depth research on a series of ancient fish fossils, the results once again confirmed that as early as the early Silurian period 438 million years ago, the South China Plate dominated by the Yangtze River Basin in China was once a vast ocean, and the ancient ocean was called the "Yangtze Sea".
This important scientific research result of the early vertebrate research team of the Institute of Paleovertebrates of the Chinese Academy of Sciences, based on the 20-year field investigation in the shallow red layer of the Silurian Lineage nationwide, was jointly completed by Gai Zhikun of the Institute of Paleovertebrates of the Chinese Academy of Sciences and Researcher Zhao Wenjin, and was jointly completed by the master's student Shan Xianren of the Institute of Paleovertebrates of the Chinese Academy of Sciences, and was helped by many scientific research peers, and was recently published in the form of a cover article in the professional journal of stratigraphy "Journal of Stratigraphy".
Distribution of Yangtze Sea and fossil fish (Shan Xianren/Paleogeographic Map, Zhongruiwen/Hubei Wuhan Ecological Restoration Map, Other Ecological Restoration Map Yang Dinghua Painting). Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
Researcher Gai Zhikun, the corresponding author of the paper, said that in the past 10 years, he led the field team to run through the early Silurian shallow sea red layer in nearly 50 counties (cities) of Suzhou, Anhui, Zhejiang, Hubei, Gan, Xiang, Yu, Qian, Sichuan, Xin, Tibet and other provinces (municipalities directly under the central government and autonomous regions), and finally found a large number of early fish fossil materials in the early Silurian marine red layer in Nanjing, Jiangsu, Changxing, Zhejiang, Ningguo and Chaohu in Anhui, Jiujiang in Jiangxi, Wuhan in Hubei, Zhangjiajie in Hunan, Xiushan in Chongqing, Tarim in Xinjiang and other areas. This provides important evidence of paleo-fish fossils for the comparison of the Red Layer of the Silogue marine facies in these areas.
The latest research on these ancient fish fossils once again confirms that as early as the early Silurian period, 438 million years ago, the South China Plate, dominated by the Yangtze River Basin in China, was once a vast ocean known as the "Yangtze Sea". The sea is further divided into the upper and lower Yangtze Seas, which are connected by a narrow waterway, and the Tarim Basin, which is 4,000 kilometers away today, is not in its current position, but is connected to China's South China Plate, so the ancient fish appearance of the two places is very similar.
Representative of fish fossils in the Rongxi Formation in northwest Hunan (photographed by Gai Zhikun and painted by Yang Dinghua). Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
The mystery of the contrast between the distinctive marine red layers of the Shilurian period
Shan Xianren, the first author of the paper, said that during the Silurian period, a series of unique shallow marine red layers were deposited on the South China Plate and the Tarim Plate, mainly a set of fine clastic rocks dominated by purple-red interspersed yellow and gray-green. Red layer sedimentation is mainly formed in shallow waters near the shore, and the existence of paleontace is the most important paleogeographic background condition for the formation of red layers. A large amount of fine hematite-containing debris carried by the river is piled up on the nearshore seabed, and if it happens to be in the receding stage of sea level decline, the seawater will show a strong oxidation state, which is very conducive to the preservation of hematite in the sediment during the diagenesis process, and eventually form the iconic marine red layer. Because of its striking color, it is easy to identify and identify in the wild.
Researcher Zhao Wenjin, the author of the paper, pointed out that the development of the Silurian marine red layer in China is closely related to its ancient geographical location. Those who are close to the ancient land, the received sources are more abundant, and the red layer is thicker; Those far away from the ancient land, received fewer sources, the red layer was relatively thin and the lateral continuity was poor. Therefore, the distribution of red layers has always been an important basis for reconstructing the ancient coastline of the Silurian period. So far, three sets of shallow sea red layers have been identified throughout the Silurian period in China, and their sedimentary time is about 438 million years, 435 million years and 425 million years ago, which are called "lower red layer", "upper red layer" and "Rhodros red layer" according to the location of each stratum. Most of these shallow sea red layers dominated by clastic rocks are missing Silurian standardized stones such as penstones and dentates, resulting in different scholars disagreeing on the division and comparison of red layers in some areas and the issue of the times, and there is still no consensus. Therefore, other phyla fossils are urgently needed to determine the epochal attribution of the red layer and to make extensive regional stratigraphic comparisons.
Representative of fish fossils of the Tangjiawu Formation in northwest Zhejiang (photographed by Gai Zhikun and painted by Yang Dinghua). Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
The armorfish were a rising star in the study of the Red Layer of the Silurian Marine
Armorfish are "regulars" in the pale marine red layer of the Chinese Silurian Period, and their hard membranous bone armor is easily preserved as fossils. The armor fish fossils of the Chinese Silurian period are not only rich in genera and numbers, but also undergo several rapid radiation evolutions, which can play a role in stratigraphic comparison. In addition, the paleogeographic distribution of armorfish is widespread, covering Anhui, Zhejiang, Jiangxi, Wuhan, Hunan, Chongqing, Yunnan, Xinjiang and other provinces and regions, providing conditions for horizontal comparison of strata.
According to researcher Zhao Wenjin, in the past ten years, with the continuous deepening of the taxonomic research of armor fish, the significance of its biological stratigraphic comparison has gradually emerged and played an increasingly important role. At present, the scientific research team has preliminarily established a comparative sequence of Sedimentary fish biological strata, in which three distinctive fish fossil combinations - Wentang combination, Maoshan combination and Yangtze combination are produced from the Lower Silurian Red Layer, the Upper Red Layer and the Rhodros Red Layer, respectively, providing important fossil evidence for the division and horizontal comparison of these three sets of shallow sea red layers.
Representative of fish fossils of the Ta tael tag formation in Xinjiang (photographed by Gai Zhikun and painted by Yang Dinghua). Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
Among them, the Wentang combination was established based on two armor fish species and several fossil fin spines of cartilaginous fish from the lower red layer of The Melting Creek Group in Zhangjiajie, Hunan. For a long time, due to the limited paleogeographic distribution of this combination, it is difficult to be applied to large-scale regional stratigraphic comparison. The field work in the past ten years has given the scientific research team a new understanding: in addition to the Rongxi Formation in Hunan, the lower red layers of Jiangxi, Jiangsu, Zhejiang, Anhui, Hubei, Chongqing, Guizhou and other places are also rich in armor fish and cartilaginous fish fossil materials. This series of new findings confirms the higher diversity and wider paleogeographic distribution of armored and cartilaginous fish in the early Tretch period, indicating that the Wentang combination has the potential for regional stratigraphic comparison on a larger scale.
The research team also supplemented and revised the wentang combination in the lower red layer through a series of new discoveries of early fish fossil materials and extensive identification of the lower red layer in the lower Yangtze River region. The revised Wentang combination is marked by the co-occurrence of basal armored fish in armor fish (Hanyang fish family, Xiushui fish family, Dayong fish family), primitive true armor fish (Aquacaryidae), primitive multigill fish (Paleomidae), and Chinese spiny fish in cartilaginous fish. The fish taxonos covered in the Wentang combination are more abundant and diverse, from the previous 3 families and 5 genera to 6 families, 14 genera and a number of undetermined genera, and their paleogeographic distribution extends from northwest Hunan to northeast Qiandong, southeast Hubei, northwestErn Gansu, northwestern Zhejiang, southeastern Anhui, and eastern Anhui. The further deepening of the Wentang combination not only provides the most direct fossil evidence for the comparison of the Lower Silurian Red Layer in the Yangtze River Basin of China, but also provides reliable ancient fish fossil evidence for solving the era of the Silurian shallow marine red layer in the future.
Representatives of fish fossils in the Houjiatang Formation and Tomb Head Formation in eastern Anhui Province (photographed by Gai Zhikun and painted by Yang Dinghua). Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences
South China and the Tarim Plate were ancient or belonged to the same sea
Gai said fossil evidence of paleontology played a key role in proving the continental drift hypothesis. The role of armor fish in proving the plate drift theory is equally important: from the existing fossil record, the 438 million-year-old early Silurian armorfish fish fossils are generally distributed along the edges of the Ancient Chinese Continent and the Yunnan Ancient Land, further confirming that the vast area of China during this period, dominated by the Yangtze River Basin, was once a vast ocean - "Yangtze Sea".
In addition, the armored fish head armor is flattened, lack of pairs of even fins, indicating that its swimming ability is weak, the ability to spread and migrate is limited, and the wide land and wide ocean have become obstacles to its spread and migration, so the armored fish has important paleogeographic significance. The early Silurian shallow sea red layer in the Keping-Bachu region of Xinjiang also produced rich armor fish, and the appearance of this fish group covers the three major groups of basal armor fish and the primitive multigill fish (ancient wood fish), which is highly consistent with the appearance of fish in South China at the same time, especially in Changxing, Zhejiang and Chaohu in Anhui. This not only provides direct evidence for the comparison between the South China Plate and the Tarim Plate 438 million years ago between the shallow sea red layer, but also suggests that the two plates, which are now 4,000 kilometers apart, may have belonged to the same sea at that time.
A section of a fish-bearing fossil in the red layer under the Chinese Silurian Tretche Order. Mountain Xianren Courtesy photo
Gai Zhikun pointed out that in addition to the evidence of ancient fish fossils, the study of invertebrate fossils also showed that the two plates of Southern China and Tarim belonged to the same zoogeographic fauna during the Silurian period; The sedimentary environment of the early Silurian period was also basically the same, and the sedimentary rock types were represented by red clastic rock systems formed in the shallow coastal seas in arid environments; The stratigraphic structure of the two places was basically the same during the Silurian period, that is, the age of the bottom layer and the cover was roughly the same. At the same time, paleomagnetic research suggests that as early as the Silurian period (443-419 million years ago), the Tarim Plate was located about 15 degrees north latitude, near the equator, and its location was farther east. At that time, it was supposed to be connected to the South China Plate, known as the Tarim-South China Joint Plate.
So why did the Tarim Basin later run from near the equator to the western frontier 4,000 kilometers away? The research team of the Institute of Paleovertebrates of the Chinese Academy of Sciences said that there is no unified view at present, and different scholars have given different explanations according to the material evidence they have. The latest view, based on the study of paleontological fossil materials combined with comprehensive analysis of paleomagnetism, stratigraphy and paleoenvironment, is:
The Tarim-South China Plate began to separate into separate plates in the late Silurian period (423 million to 419 million years ago), and the main reason for its disintegration may be due to the huge energy of the Changtang and Qamdo land masses rushing from south to north, thus knocking the joint plate apart. After the dissolution of the Joint Plate, the Tarim Plate began to drift slowly northwest in a clockwise direction, reaching its current position around the Late Permian (252 million years ago), while the South China Plate slid about 800 km eastward. "As the Indian plate continues to dive northward, it remains to be seen whether the Tarim plate will drift northward." The research team said. (End)
Representative of fish fossils in the Qingshui Formation in northwestErn Jiangxi (photographed by Gai Zhikun and painted by Yang Dinghua). Photo courtesy of Institute of Paleovertebrate Vertebrate, Chinese Academy of Sciences