GEOGRAPHY

438 million years ago, there was an ancient ocean in the Yangtze River Basin, the Yangtze Sea


Recently, the research team of the Institute of Paleontology and Paleoanthropology of the Chinese Academy of Sciences (hereinafter referred to as the “Institute of Paleovertebrates”) published a cover article in the Journal of Stratigraphy, reporting the important results of the 20-year field expedition of the early vertebrate team of the Institute of Paleovertebrates of the Institute of Paleovertebrates of the Chinese Academy of Sciences nationwide in the Shallow Red Layer of the Silurian Period.

In the past 10 years, Gai Zhikun, a researcher at the Institute of Paleovertebrates, has led a field team to run through the early Silurian shallow sea red layer in nearly 50 counties (cities) across the country, and finally found a large number of early fish fossil materials, thus providing important ancient fish fossil evidence for the comparison of the Marine Red Layer of the Silurian in these areas.

The study found 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.

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Distribution of Yangtze Sea and fossil production areas of ancient fish (red represents shallow sea) (Shan Xianren draws a paleogeographic map, Zhongruiwen provides an ecological restoration map of Wuhan, Hubei Province, and other ecological restoration maps are drawn by Yang Dinghua)

The mystery of the contrast between the distinctive marine red layers of the Shilurian period

During the Silurian period, the deposition of China’s South China Plate and Tarim Plate formed a series of unique shallow marine red layers, mainly a set of fine clastic rocks dominated by purple red, yellow and gray green.

Red layer sedimentation is mainly formed in shallow waters near the shore, and the existence of paleontace is the paleogeographic background of the formation of red layers. The rivers carry large amounts of hematite (Fe?). O?) fine debris, accumulated on the nearshore seabed, if it happens to be in the receding phase 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.

The characteristics of the development of the red layer are also closely related to its ancient geographical location: those who are close to the ancient land, the received material source is more sufficient, and the red layer is also thicker; Far from the paleocene, fewer sources are accepted, the red layer is relatively thin and the lateral continuity is poor, so the distribution of the red layer has been an important basis for reconstructing the ancient coastline of the Silurian period.

Armor turtle – A rising star in the contrast of the Red Layer of the Silurian Marine Phase

Armor fish is a common molecule in the pale marine red layer of the Silurian period in China, and its hard membranous bone armor is easily preserved as a fossil.

The armor fish fossils of the Chinese Silurian period are not only rich in genera and numbers, but also underwent several rapid radiation evolutions and can play a role in stratigraphic comparison. In addition, the paleogeographic distribution of armorfish is widespread, providing conditions for horizontal comparison of strata.

In recent years, with the continuous deepening of the taxonomic research of armor turtles, the significance of their biological stratigraphic comparison has gradually become prominent, and it has played an increasingly important role.

At present, Chinese scholars have initially established a comparative sequence of Sedimentary fish biological strata, in which three distinctive fish combinations – Wentang combination, Maoshan combination and Yangtze combination are produced in the Lower Silurian Red Layer, The Upper Red Layer and the Rhodrotic Red Layer, which provides important fossil evidence for the comparison between these three sets of shallow sea red layers.

The Wentang combination was established based on two armor fish species and a number of fossil fin spines of cartilaginous fish from the lower red layer of The Melting Creek Group in Zhangjiajie, Hunan. In addition to the Rongxi Formation in Hunan, the lower red layer in many places also produces abundant fossil materials of armored fish and cartilaginous fish. This series of new discoveries confirms the higher diversity and broader paleogeographic distribution of armored and cartilaginous fish in the early Trech period, suggesting that the Wentang combination has greater potential for regional stratigraphic comparison.

This study summarizes and analyzes the fish fossils and fish fossil combinations in the five lower red sedimentary areas of the Silurian period in China, enriching the biodiversity of the Wentang group, expanding the paleogeographic distribution of the group in the Yangtze region, and providing reliable fossil evidence for the comparison of the early marine red layer of Treqi in the Yangtze region of the Yangtze region.

Ancient fish fossils tell you where the Tarim Basin came from

Paleontological fossil evidence plays a key role in proving the continental drift hypothesis.

The water dragon is a kind of mammal-like reptile that lived about 200 million years ago, mainly living on land, unable to migrate across the sea, but their fossils are widely distributed in the late Permian – Early Triassic strata in Xinjiang, southern Africa, India, Antarctica and other places in China, and their wide distribution across the ocean strongly illustrates these fossil points, which may have been in the same united continent at that time – Gondwana Continent.

The early shallow sea red layer of the Silugi Trichi in the Keping-Bachu region of Xinjiang also produced rich armor fish, and the appearance of the fish group covered the three major groups of basal armor fish and the primitive multi-gill fish, which was highly consistent with the fish appearance in Southern China at the same time, especially in Changxing, Zhejiang and Chaohu in Anhui, indicating that the two plates separated by 4,000 kilometers today may have belonged to the same sea area at that time.

According to the researchers, in addition to the evidence of ancient fish fossils, the study of invertebrate fossils also shows that South China and the Tarim Basin belong to the same zoogeographical fauna. The sedimentary environment of the two in the early Silurian period was also basically the same, and both belonged to the red clastic rock system formed in the shallow sea in the arid environment. In addition, the stratigraphic structure of the two was basically the same during the Silurian period, i.e. the age of the bottom layer and the cover was roughly the same.

During this period , the Semitic strata on both plates were covered by late Ordovician strata , which were covered by late Devonian strata. Paleomagnetic studies suggest that as early as the Silurian period (about 443-416 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. (Source: China Science Daily, Hu Minqi, Teng Wenyu)

Related paper information:https://doi.org/10.19839/j.cnki.dcxzz.2022.0011



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