What is the Paleogene Period?

Paleogene Period (65 million years to 23.3 million years ago) The Early Tertiary is Paleogene. The same is the earliest historical stage in the Cenozoic, also known as the old Tertiary, originally a sub-Era of the Tertiary. Its original meaning refers to the occurrence and enlightenment of modern life. The Early Tertiary period began 65 million years ago and ended 23.3 million years ago. The strata formed during this period are called the Lower Tertiary.

Early Tertiary includes

In 1933, British scientist Layle C., studying the tertiary mollusk fossils in the Paris Basin, France, found that the newer the stratum, the more mollusks it contains, the more species of the same species. He divided the Tertiary into

The early Tertiary experienced relatively short time in the history of the earth, but the sediments formed during this period are significantly different from the Mesozoic. The lower Tertiary is rich in fossils of various biological groups. These fossils play a key role in the division and comparison of the Lower Tertiary and the establishment of standard sequences and layer profiles. In the early Tertiary, many regions in the world formed stratigraphic strata with distinct boundaries of marine facies and marine-terrestrial facies. For example, the standard sequence of the Tertiary in Western Europe was divided into 11 stages. Terrestrial sediments dominated by lacustrine facies have also formed in regions such as central and western North America and central Asia, especially in the basin distribution areas of the Rocky Mountains in the United States.

In addition to the rock formation, paleomagnetism, and isotope measurements, the Lower Tertiary is mainly divided by contrast methods such as paleontology (or fauna), sequence, and layer profile. Due to the different evolutionary rates of various species, the sediments in different places are not simultaneous, so the division of strata often does not match the argument provided by the above studies, so that the contrast and the boundaries are often controversial. For example, the chronology of the Daningian (Denmark) and Aquitaine (France) in marine strata is different. Some people think that the Echinoids of the Daningian stage have the characteristics of the Late Cretaceous, but according to the study of the areas around Crimea, the Caucasus and the Caspian Sea and Denmark, southern Sweden, planktonic foraminifera and echinoderm fossils, they are related to the Paleozoic The Pliocene type is closely related. Therefore, many scholars believe that the boundary between Mesozoic and Cenozoic should be placed between the Maastrichian stage and the Daningian stage. However, some scholars still believe that the boundary between Mesozoic and Cenozoic should be drawn between the Daning and Monty stages. The problem of belonging to the Aquitanian, paleontologists have studied from mollusks and mammals that its biome has a clear inheritance relationship with the fossils of the lower Stampian, and there are certain differences compared with the late Tertiary. They advocated that the Aquitanian stage was set as the upper boundary of the Oligocene. However, the marine microfossils of the Aquitaine are closer to the Bordeaux of the Early Miocene, and it represents a major transgression period in Europe, so it is appropriate as the bottom of the New Tertiary. Many scholars advocate that the boundary between the lower tertiary system and the upper tertiary system should be placed between the Qat and Aquitaine stages. In contrast, the tertiary system in the terrestrial facies is more consistent with the standard, and generally follows the sequence of the classic American regions. The lower boundary of the lower tertiary system is the bottom of the Belkaian stage, which indicates the disappearance of dinosaurs, and mammals have the placenta.

The tertiary line in China is fully developed. In hundreds of basins across the country, very distinctive terrestrial strata are widely distributed. The discovery of Paleo-Pinocene in the world is rare, mainly in the United States. Asia found only one location in Mongolia in the early 20th century. Since 1960, China has successively discovered a number of important Cenozoic sites in eight provinces and autonomous regions. The Upper Lake Formation and the Upper Chijiang Formation of the lower continental palaeozoic in China are represented. Hundreds of animal fossils have been discovered in the Paleozoic, including more than 100 vertebrates. The Eocene has been well developed in China. For example, the typical sequence of the Aldingmanian and Xylamurian stages in Inner Mongolia has been recognized internationally. The study of the Oligocene system started late, and many discoveries have been made in Inner Mongolia, Ningxia, Xinjiang, Guangxi, Yunnan and other places, which provides a good basis for the improvement of the Oligocene sequence. The lower boundary of the terrestrial tertiary in China is roughly equivalent to the upper lake formation of the Bemalambda fauna and the bottom of the Wanghudun formation. The upper boundary of the terrestrial fauna may contain Paraceratherium-Tataromys. The level of the fauna, such as the top of the Igbulag Formation in Inner Mongolia.

Tertiary under the Chinese marine facies

With the end of the Cretaceous, significant changes in climate have brought about a change in plant life and increased diversity in the landscape. Angiosperms appeared during the Early Cretaceous and were extremely prosperous by the early Tertiary. The vegetation previously composed of ancient fern and various pine and cypress was gradually replaced by angiosperms. At this time, the angiosperm was basically an arbor. No matter from the new family, the new genus, or the number of individuals, the number of individuals increased greatly compared with the Mesozoic. Tropical and subtropical plants such as palms have penetrated far into the Arctic. The development of flowering plants and grasses has created the necessary conditions for the prosperity of the animal kingdom (such as insects and vertebrates).

Continental drift, zoning of climate, and changes in temperature have profound effects on the evolution, development, and ecological environment of life. The animal kingdom has marine, terrestrial, and brackish water adapted species. Among them, vertebrate changes are the most prominent. Marine reptiles such as snake-necked dragons and marine lizards, which were widely distributed in the late Mesozoic, were replaced by marine mammals such as small cetaceans and sea lions in the early Tertiary. On land, dinosaurs that dominated the Mesozoic era basically disappeared, while mammals that were not prominent in the Mesozoic era multiplied rapidly, and they occupied various ecological areas of reptiles in the past. The continents and islands are full of birds that are close to modern. The transition from the predominance of Mesozoic reptiles to the proliferation of early Tertiary mammals is a major event in the evolution of life history on Earth. Why the mass destruction of dinosaurs remains a mystery. Some scientists believe that a comet or other star has fallen on the earth, causing a sudden change in the climate or causing a lot of acid rain to fall, causing the extinction of a group of animals, dinosaurs. Other scientists believe that the volcanic eruption and climate change have led to sudden changes in the plant kingdom and caused species extinction. ^[1]

At that time, paleontological features: Gondwana ancient land further divided, Australia and Antarctica separated and gradually moved northward. The Indian block was connected to the hinterland of Asia during the Eocene, forming the South Asian subcontinent. From time to time, South and North America meet in the "Panama Isthmus", causing migration and exchange of some species of fauna in the two places. Before the Eocene in the early Eocene, there was still a barrier between the "Ural Sea" and the Himalayan Sea. The shallow sea may disappear gradually before and after the Eocene, and the fauna of the Eurasian continent is getting closer. At the beginning of the Tertiary, the eastern and western parts of Eurasia were connected to North America, and the exchange between Asia and North America through the "Bering Land Bridge" did not gradually form the main route for the spread of terrestrial fauna in the northern hemisphere until the late period. Greenland and Scandinavia have drifted closer to where they are today. The Arabian Peninsula was separated from Africa, and later connected to Asia, and the Red Sea emerged. A huge fault zone has begun to appear in eastern Africa. In the middle and late period of the Tertiary, the final formation of the Asian continent and the formation of China's eastern marginal waters laid the framework for China's modern terrain. ^[2]

Due to the expansion of the ocean floor and the disintegration of the paleocontinent, major changes have taken place in the entire geological structure pattern and paleogeographic environment in the world. In the early Tertiary, the ancient Mediterranean Sea (Tethys Sea) finally disappeared, the Asian continent finally formed, the rise of the Qinghai-Tibet Plateau, the Alps, the Himalayas, the Rocky Mountains, and the Andes and other modern mountain systems have successively formed. With the emergence or disappearance of the Panama Isthmus, the climatic zone is gradually becoming apparent, and the natural environment on the earth is developing towards diversity.

In the early Tertiary, due to the different positions of the continents from modern times, plate drift, changes in ancient latitudes, and temperature were also different from those of today. From the late Cretaceous to the Paleozoic Northern Hemisphere, the annual average temperature dropped by about 3 ° C. By the end of the Paleocene, the temperature rose once. However, the temperature began to decline in the late Eocene, and gradually returned to the original level until later. In the late Early Tertiary, China's climate had obvious north-south subzones. For example, the north and south are two moist zones and the middle is arid zone. The climatic zone spreads obliquely with today's latitude. ^[3]

The most striking of the Early Tertiary is the influence of the Himalayan movement. This stage is the period when the Qinghai-Tibet Plateau began to rise, and at the same time, the large piedmont depressions and the eastern sedimentary centers in western China formed. Although large-scale Mesozoic volcanic activity around the world has weakened to the late Cretaceous, generally speaking, the early Tertiary volcanic activity is still relatively frequent, mainly volcanic eruption mainly based on the basic. However, there are medium-acid volcanic materials from the Gangdise Mountains in Tibet to Lhasa. Taiwan also has acid lava distribution. ^[4]

In the early Tertiary, due to the diversified sedimentary environment, not only the huge mullite construction was formed in China, but also various types of genesis of continental facies, marine facies, and sea-land transitional facies were formed in a large area. These sediments are rich in resources, mainly oil, coal, oil shale, copper-bearing sandstone, and various salts. The original substance that produces petroleum is organic matter. Due to the accumulation of a large number of animal and plant remains in the early Tertiary, oil fields existed not only in marine formations but also in terrestrial formations. Oil is mainly found in long-sinking depressions and large- and medium-sized lake sedimentary basins, such as in the early and early Middle Tertiary relevant horizons (see Petroleum genesis). Coal is controlled by certain structural and climatic factors, and it is common in warm temperature (subtropical) regions. Due to the warm and humid climate, coal is suitable for the formation and accumulation of coal (see coalification). The Early Tertiary is an important coal-forming period. It is mainly found in the north of the Qinling Mountains, east of the Helan Mountains-Liupan Mountains, and the Zhujiang-Youjiang areas south of Nanling in China. At the same time, most of the coal-bearing horizons contain oil shale layers, such as Fushun and Maoming in China, which have thick oil shale layers. Early Tertiary salt deposits are quite abundant, mainly including gypsum, rock salt, thenardite, trona and potassium salts. In addition to having deep and well-sealed basins, the formation of salts is more important to have a longer-term arid climate. As early as the Tertiary, China's arid zone occupied a considerable area and was a natural place for salt accumulation. In addition, there are copper-bearing sandstone and uranium oxide deposits.

At the end of the Cretaceous, based on the north-northeast uplift and depression formed by the early Yanshan movement in the eastern part of China, a series of north-northeast faults and rift zones were generated. The early Tertiary coal-bearing strata in a coal accumulation area in Northeast China and North China were mainly deposited in these north-northeastward fault depressions, followed by the margins of the Songliao Depression and North China Depression. There are more than 40 large and small coal-bearing basins. The main ones are Fushun, Meihe, Shenbei, Yongle, Yilan, Shulan, Hunchun, Huangxian and other coal fields. Among them, Fushun and Yilan are long-flame coal, and the others are lignite. Fushun Coalfield contains the best coal, with 3 layers of coal and a single layer with a maximum thickness of 97m. The famous Fushun open-pit coal mine is the main mining layer. The second is the Shenbei Coalfield, which contains two layers of coal, and the maximum thickness of a single layer is 18.5m. Huangxian coalfield contains 4 layers of coal, and the maximum thickness of a single layer is 9.88m. Fushun, Yilan, Shenbei, and Huangxian coalfields also contain oil shale formations.

There are also early Tertiary coal-bearing strata in the southwest of the South China-Southern China coal gathering area. The main ones are Maoming, Nanning, Baise and other coal fields. Its coal-bearing property is worse than that in the Northeast.

China's early Tertiary coal-bearing strata are mainly terrestrial sediments. Although there are shallow marine facies and lagoon facies in the coastal areas of South China, they are still clastic rocks. Does not contain karst water. Its overlying and underlying strata are also not threatened by karst water.

After the accumulation of early Tertiary coal measures, their settlement depth and thickness of overlying strata are generally not large, and the temperature and pressure experienced by coal strata are low; the time since coal formation has been relatively short and the structure experienced There is also less exercise. Therefore, the consolidation degree and petrochemical degree of coal measures rocks are low, the original pores between the particles that make up the rocks are still basically preserved, the sandy rocks are in a loose or semi-loose state, and the argillaceous rocks also have a large plasticity, and the fractures are generally Not very developed. Pore water is dominant in coal-bearing strata, and fissure water has only local significance. The particle size composition, sortability and cementation degree of the rock play a leading role in its water content and water permeability. Faults generally only displace or dock the aquifers and aquifers of the two disks, and the fault fissure zone and its water-conducting effect are generally not very significant. However, in the Fushun and Yilan coal fields in the northeast, the consolidation degree and petrochemical degree of coal measures rocks are slightly higher, which can be in a semi-rigid state, and fissures are relatively developed. Fissure waters also have a relatively important status, especially in weathered zones and fault zones. Significantly. However, compared with the Paleozoic and Mesozoic coalfields, the degree of fissure development and its water-conducting effect are still inferior. .

When mining early Tertiary coalfields, they often encountered great difficulties in engineering geological conditions. One is the quicksand breaking into the shaft, the other is the serious deformation of the roadway, and the third is that the open-air slope is unstable.

When the unconsolidated saturated silt layer contains a certain amount of hydrophilic minerals (such as montmorillonite, illite, hydromica, etc.), this silt layer is called quicksand layer. Quicksand has a large water holding capacity and a small water supply. Water and sand are not easy to separate. Once perturbed or vibrated, it quickly liquefies and flows in a fluid state with an angle of repose close to zero. There are many thick layers of quicksand on the top and bottom of the coal seam in the Shulan coal field in Jilin Province, which caused many difficulties to the coal field geological exploration, coal mine construction and production. When the roadway exposes the quicksand layer or unclosed boreholes that pass through the quicksand layer, or when the mining area or the roadway roof falls and touches the quicksand layer, or the thickness and strength of the water barrier between the bottom of the coal seam and the underlying quicksand layer When resisting the pressure of the underlying quicksand layer and causing bottom drum and rupture in the mining area or the floor of the roadway, quicksand will collapse into the well and roadway, engulfing part of the roadway and discs, and destroying the whole production well; Death; and it was extremely difficult to clear and restore the well. Large-scale quicksand erosion can also cause ground subsidence. Endangering ground construction safety.

When mining this type of coal field, special methods must be used to predrain it for a long time in advance, so that quicksand loses its fluidity before it can be safely mined. The Shulan Coal Mine has accumulated a wealth of experience in the struggle against quicksand layers.

As for the general water-bearing sand layer (so-called "false quicksand"), although it can also burst people and fill part of the roadway, its flow and harm are much less than the real quicksand. In addition, water and sand are easy to separate, and it is easier to dry out and treat, except that the amount of water is large.
The clay rock in the Early Tertiary coal measures has a relatively human plasticity. Once the roadway is exposed, it loses the static balance of its original meter, and moves slowly toward the roadway, which causes the roadway to produce a bottom drum, a sag, a bump, and a section. Shrinkage, breakage of brackets, arching and bending of rails make maintenance of shafts very difficult. Shenbei Coalfield in Liaoning Province, Meihe Coalfield in Jilin Province, Hunchun Coalfield, Huangxian Coalfield in Shandong Province, Maoming Coalfield in Guangdong Province, Nanning and Baise Coalfields in Guangxi Province are all deeply troubled in mine production.

When the tertiary coalfields are opened by open-air methods, the problem of slope stability is more complicated than that of Paleozoic and Mesozoic coalfields. Because the lithology is soft, its internal friction angle and cohesion are generally small, so the slope is not easy to stabilize. It is also because of its high water holding capacity, plasticity, easy expansion, disintegration and deformation, and low bearing capacity. It is easy to sink or reverse under the action of mining machinery and vehicles. Draining, easier to flow ^ Therefore, when mining the tertiary coal field by open-air method, a smaller slope angle and stricter dredging measures must be used. Especially when there is montmorillonite, tuffy clay, clay layer with more hydrophilic minerals, and quicksand layer in the floor of coal seam, the problem is more complicated. The tuff below the coal seam floor of the Fushun Open-pit Mine (or the tuff is stuck on it) has caused large-scale sliding of the open-air slope many times, causing significant losses. Although large-scale hydrogeological and engineering geological work has been carried out and various measures have been taken to prevent and treat, the hidden danger of slope slippage has still not been completely eliminated.