The Cambrian period was a geological time of about 550 million to 540 million years ago in geological time. It can be divided into three periods: the Cambrian period (540 million to 570 million years ago), the Mesocambrian period (523 million to 540 million years ago), and the Post Cambrian period (550 million to 523 million years ago).

[Edit this section] Great development of marine invertebrates

The Cambrian period is the first period of the Paleozoic Paleozoic in the geological age division, about 540 million to 510 million years ago. The Cambrian is the beginning stage of modern organisms and the period when modern life on Earth began to appear and develop. The Cambrian period is very far and unfamiliar to us. The characteristics of the continental earth in this period are completely different from today. The Cambrian period is often called the "Trilobite Era", because there are mineralized trilobite hard shells in the Cambrian rocks that are richer than other groups. At that time, there were rich and diverse and relatively advanced marine invertebrates, and a large number of fossils were preserved, which made it possible to study the conditions of the biological world at that time, and to use biostratigraphy methods to divide and compare strata, and then study the relatively complete development history of the organic and inorganic worlds. However, the Chengjiang fauna tells us that the diverse animal phyla that live on the earth appeared almost at the same time soon after the Cambrian period began.

The Cambrian period is the beginning of the Phanerozoic Eon, marking a new scene in the history of biological evolution on Earth. In just a few million years after the beginning of the Cambrian period, a large number of multicellular organisms, including almost all groups of prevalent animals, suddenly appeared. This explosive biological evolution event is called the "Cambrian Explosion". Marine invertebrates with shells and bones tend to prosper. They live in benthics and feed on tiny seaweeds and organic matter particles. Among them, the most prosperous one is the arthropod trilobite, so the Cambrian period is also called the "Trilobite Age", followed by brachiopods, ancient cup animals, echinoderms and gastropods, the biology of the Cambrian period is strange, and we are now on Earth.

The creatures that can be seen are very different. The more famous ones are the Chengjiang fauna in Yunnan in the early Cambrian period and the Burgis shale biota in the middle Cambrian period in Canada. The Cambrian biological world mainly consists of marine invertebrates and marine algae. Many advanced phylas of invertebrates such as arthropods, echinoderms, mollusks, brachipods, and pythons. Among them, the Trilobites in the Arthropods are the most important, followed by brachipods. In addition, ancient cups, paleomorphs, soft tongue snails, odontic snails, nautilus, etc. are also very important. Putting aside the odontic stones, there are many other representatives of higher chords, such as the Chinese eels, Yunnan fish, and Haikou fish in the Chengjiang fauna in Yunnan in my country, the skin worms in the Burgis shale in Canada, and the duck scale fish in the U.S. Cambrian.

In humid lowlands, lower plants of moss and lichens may be distributed, but they still lack real rhizomes and are difficult to live in dry areas; invertebrates have not yet evolved to adapt to living in the air. There were no real terrestrial creatures in the Cambrian period, and the continent lacks vitality and is desolate.

Paleontology quotes the term "big explosion" to describe the sudden explosion of biodiversity. According to the sudden diversity and complexity of trace fossils and small-shell fossils at the beginning of the Cambrian period, the theory of "big explosion in Cambrian period" was proposed before the discovery of the Chengjiang fauna, but there is little knowledge of the structural characteristics of the animals and animal communities produced by the "big explosion in Cambrian period". Even the famous Canadian Burgis shale fauna fossils were more than 10 million years later than the "big explosion in Cambrian period". It is impossible to answer what specific life was found in the oceans in the early Cambrian period.

The geological era of the Chengjiang fauna is in the "Cambrian explosion". It allows us to see the true appearance of the fauna 530 million years ago. Various animals quickly originated and appeared immediately during the "Cambrian explosion". Almost all animal species living on the earth now exist at the same time, rather than slowly changing after a long period of evolution. It pushes the history of animal diversity to the early Cambrian period.

The Cambrian biological forms were strange and very different from the present creatures on Earth. The oldest species of fish also appeared in this era, the Haikouichthysercaicunensis, the fossil was excavated in the Chengjiang fauna.

[Edit this section] The age of global flooding

During the Cambrian period, animals with hard shells appeared in large numbers, many continents were flooded by shallow seas, and the supercontinent Gondwana was forming near the Antarctic.

The distribution map of the Earth's sea and land in the late Cambrian period was formed in the supercontinent Pannotia in the late Precambrian period (about 600 million years ago). It began to split during the Paleozoic period. A new ocean, the Iapetus Ocean, expanded between the ancient continents of Laurentia (North America), Baltica (Baltica) and Siberia. The supercontinent Gondwana was combined on the Pan-African fold belt to form the largest continent at that time, extending from the equator to the Antarctic.

During the Ordovician period, warm seawater deposited limestone and salt rock in the equatorial region of Gondwana (Australia, India, China and Antarctica), and at the same time, the deposition of glaciers and ice floats were deposited in the Antarctic region of Gondwana (Africa and South America).

Also known as the "Prepalaeozoic", the geological era before the first Paleozoic period - the Cambrian period (about 600 million years ago).

[Edit this section] The long precambrian period

The beginning of the Cambrian period marked the beginning of the Earth's entry into a new stage of great biological prosperity. Before the Cambrian period, the Earth had already formed, but it was silent for a long process of billions of years. At that time, no creatures of various species appeared on the Earth. In this way, scientists called the long and lacking life period before the Cambrian period the Precambrian period. The Precambrian period accounted for about five-sixths of the total geographic history time. Since there was no sufficient biological basis, we know very little about this history of the Earth.

According to valuable information on signs of life activities and for the sake of research convenience, geologists divided the long Precambrian period into two parts: the Ancient and Proterozoic. Before the Ancient period (the beginning of the formation of the earth - 3.8 billion years ago), there were many different names.

The ancient times were far away from us, with a time limit of about 3.8 billion years to 2.6 billion years ago, and it was 1.2 billion years. The ancient times were the initial stage with clear historical records. During this long 1.2 billion years, it was the initial period after the formation of the earth. Children's mountains and deserts formed everywhere on the surface. Due to the age of time, it is indeed difficult to find fossils, and people know very little about the life activities during this period. However, in the second half of the 20th century, scientists successively gained major gains in South Africa and Australia, and found stromatolites in sedimentary rock formations with less severe metamorphism, which is the product of microorganisms and algae activities. In addition, people also analyzed a large number of organic compounds (such as benzene, hydrocarbenzene, etc.) and cyclic compounds (such as furan, methanol, acetaldehyde, etc.) in these ancient rock formations. In a set of ancient sedimentary rocks in South Africa, scientists took the lead in

The precision observation instruments have been introduced to discover more than 200 ancient cell fossils that are very similar to prokaryotic algae. These micro-body fossils are generally oval and have a smooth organic matter membrane. This is the oldest and most primitive fossils discovered so far, and the most convincing biological evidence found in ancient strata. From the biological world, this is the primary stage of the emergence of primitive life and biological evolution. At that time, there were only a small number of prokaryotes, and they only left a very small record of fossils. From the non-biological world, the Archaic universe was a period of thin crust, steep geothermal gradient, strong and frequent volcanic-magma activities, and rock strata were generally deformed and metamorphic. Both the atmosphere and the water circle lacked free oxygen to form a series of special sediments. It was also a period of formation and growth of silicon-aluminum crust, and another important period of mineralization.

The time limit for the Proterozoic period was from 2.6 billion years ago to 570 million years. In this period of geography, prokaryotes evolved into eukaryotic organisms, forming the fungus-algae era in the geography history period. People have discovered micropaleozoic fossils, macroscopic algae fossils and stromatolites in the ancient strata of this period. In our China alone, paleontologists have discovered more than 80 genera, nearly 200 species of micropaleozoic fossils in different periods of the Proterozoic period. Life further flourished in the Proterozoic, at that time

The earth is no longer deserted. In the early days, some continental plates with wider range, larger thickness and relatively stable appearances on the surface. Therefore, the Proterozoic tectonics showed relatively stable characteristics than the Ancients. The atmosphere in the late early Proterozoic period already contained free oxygen, and with the increasing prosperity of plants and the continuous strengthening of photosynthesis, the oxygen content of the atmospheric circle continued to increase. The middle and late Proterozoic algae plants were already very prosperous, which was obviously different from the Ancients.

In the late Proterozoic period, it was named the Zhendan period from about 850 to 570 million years. This is because this period has the significance of inheriting the past and opening up the future in the evolution of life, and its name is in China.

"Sinian" means China. Ancient India called China the "Sinian". German geologists first used it in stratigraphy. Later, many scholars imitated it, but the meaning was different. Later, geologists redefined the Sinian period. Li Siguang, a famous geologist in my country, and others established a complete Sinian geological profile in the Three Gorges of the Yangtze River. This is the famous east profile of the gorge, which provides the world with the basis for stratigraphic comparison.

The Sinian Chronicle has clear biological evidence, and low-level small hard-shelled species appeared in the animal world, as well as a large number of naked high-end animals. The latter is the Ediacara fauna found in Australia. In terms of plants, it is manifested as the further prosperity of advanced algae (such as red algae, brown algae, etc.), and macroalgae also developed rapidly. At this time, the earth had completely changed its dead silent and lifeless appearance.

The Sinian period is a unique geological history stage in the last period of the Proterozoic period. From the perspective of biological evolution, the Sinian system has an important difference from the Proterozoic world that does not contain reliable animal fossils because of its hard shell. However, compared with the Cambrian era rich in animal fossils with shells, the fossils contained in the Sinian system are not only monotonous in species, but also have very limited distribution. Therefore, the animal fossils in it cannot be used for effective biological stratigraphic work. The most prominent feature of the Sinian biological world is the later outbreak.

There are many species of hard-shell-free metazoans, and a small number of small animals with shells appeared in the end. Advanced algae further flourished, and some new types of micro-paleophytes appeared. The stromatolites tended to flourish in the early Sinian period, and the number and species suddenly decreased in the later period. From the tectonic condition of the lithosphere, several large and relatively stable continental plates appeared on the surface during the Sinian period, and above them were typical capping deposits, similar to the Paleozoic. Therefore, the Sinian period can be considered a transitional stage between the Proterozoic and the Paleozoic period.

The Ediacara fauna is mainly composed of organisms similar to jellyfish, worms, and squids, and is mostly preserved as imprint fossils. Although their shapes and structures are very primitive, they are considered one of the most important paleontology discoveries in the 20th century. This discovery has caused the scientific community to abandon the traditional concept that metazoan fossils were long believed to be impossible before the Cambrian period. The so-called metazoan refers to various multicellular animals relative to protozoans.

[Edit this section] The famous Zhang Xia Cambrian stratigraphic section

The Cambrian strata development and exposure in the areas of Zhangxia, Gushan and Mantou Mountain in Shandong are very good, and the transportation is conveniently located close to the Jinpu Railway. It was valued by geologists at home and abroad as early as the end of the 19th century. In 1903, American geologists B. Verris and E. Blackweld measured the profiles in Zhangxia, Gushan, Laiwu Jiulong Mountain, etc., collected fossils, and made a preliminary division of the Cambrian strata. Their research results were officially published in 1907, and Zhangxia was selected.

The Cambrian strata in the Gushan area are divided from bottom to top into steamed bun shale, Zhangxia limestone, Gongshan shale, and fried rice-dian limestone. Later, American paleontologist Bi Ketuo (1913), Japanese Endo Takaji (1939), and Kobayashi Shiichi Kobayashi (1941, 1942, 1955). All of them have studied the biological fossils in the Cambrian strata in the Gushan area. Professor Sun Yunzhu, a famous geologist in my country, has been studying Zhang Xia since 1923.

The Cambrian system in the Gushan area has been studied for more than 20 years and divided the Cambrian strata. In 1953, Lu Yanhao and Dong Nanting re-observed the Cambrian standard profiles in Zhang Xia and Gushan areas. The most important one is to divide the steamed bun shale of B. Veris and E. Blackweld from bottom to top into the steamed bun group, Maozhuang group, and Xuzhuang group. The first two groups were placed in the Lower Cambrian, the latter group was classified into the Middle Cambrian, and the fried rice-dian limestone was divided into Fengshan.

The group and Changshan Group identified the Cambrian Department in Zhangxia as 7 units and 17 trilobital fossil belts. Since then, relevant geological colleges, such as Beijing Institute of Geology, and Shandong Provincial Geology Bureau, have successively conducted a large number of field observations, profile measurements, indoor identification and special research on the Zhangxia Cambrian strata profile, and obtained rich practical data, supplemented and improved the basic data of the profile from different angles, and further improved the research level of the profile.

The Cambrian stratigraphic section of the Zhangxia Cambrian system is divided into seven stratigraphic units of the lower, middle and upper stratigraphic units, namely the Mantou Group of the Lower stratigraphic units, the Maozhuang Group of the Central stratigraphic units, the Xuzhuang Group of the Zhangxia Group, the Gushan Group of the Shangtong, the Changshan Group and the Fengshan Group of the Fengshan Group. The description from old to new is as follows:

The Mantou Formation is mainly composed of variegated shale, muddy, dolomite limestone, and other fuchsia. The bottom is not integrated on the flesh-red flakes of the Taishan complex. The lower limestone contains magnet nodules and bands, the upper shale has fine horizontal stratigraphy, and the middle shale contains trilobite fossils ~ Zhonghua Ledriki worms. The thickness is 119 meters.

The Maozhuang Formation is mainly composed of purple mica shale and limestone. It contains trilobites, brachiopods and algae fossils. It has a thickness of 39 meters.

The Xuzhuang Formation is mainly composed of purple-gray shale and oval limestone. The lower limestone and gray matter siltstone are often obliquely stratigraphed or interlaced. It contains trilobite fossils such as Xuzhuang worms and brachiopod fossils. The thickness is 73 meters.

The Zhangxia Formation is mainly composed of oval limestone and algae limestone, with medium-colored shale, containing trilobite fossils such as derella worms. The thickness is 198 meters.

The Gushan Formation is mainly composed of bamboo leaf limestone, lump limestone and yellow-green shale. It contains fossils of trilobite such as butterfly insects, bat insects, and has a thickness of 51 meters.

The Changshan Formation is mainly composed of layered limestone, bamboo leaf limestone with red oxidation circles, and purple shale. It contains fossils of trilobite such as Zhuangdi worms and Haolishan worms. It has a thickness of 70 meters.

The Fengshan Formation is mainly composed of amygdala and bamboo leaf limestone. It contains trilobite fossils such as Jinan insects, square-headed insects, as well as sea lily stems and brachiopod fossils. The thickness is 130 meters.

The standard profiles of the Cambrian strata of the Zhangxia are located in Mantou Mountain, Hutou Cliff, Huangcaoping, Tang Wangzhai, Fanzhuang and other places in Zhangxia and Gongshan areas. Among them, Mantou Mountain is the profile of Xuzhuang Formation, Maozhuang Formation, Mantou Cliff ~ Huangcaoping is the profile of Zhangxia Formation, Tang Wangzhai is the profile of Gushan Formation, Changshan Formation, Fanzhuang is the profile of Fengshan Formation.

Mantou Mountain is located 2 kilometers south of Zhangxia Town and the west side of National Highway 104. It is named because of its shape like steamed buns. There are two small villages called Xuzhuang and Maozhuang on the northern foot of the mountain. It is the location of the founding and life protection of the Mantou Group, Maozhuang Group, Xuzhuang Group, and Xuzhuang Group in the standard strata section of the Zhangxia Cambrian period.

The Zhangxia Cambrian stratigraphic profile is located north of the main peak of Mount Tai, located on both sides of the transportation trunk line between Tai'an and Jinan. It is convenient to transport, simple structure and complete exposure, which is very conducive to on-site observation and research. It is one of the longest and most researched stratigraphic profiles in my country's geology history. After the 1959 National Stratigraphic Conference, it was officially identified as the standard stratigraphic profile of the Cambrian system in northern my country. It plays an important role in the comparison of Cambrian stratigraphics in different regions of my country and the comparison of International Cambrian stratigraphics. It is also a number of Cambrian paleogene species (Kaoliz, Kaoliz
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