Basin formation mechanism, the reasons for basin formation

The transformation of tectonic deformation in Erlian Basin is related to the tectonic environment in which it is located. The change of mechanical properties changed the paleo-Asian tectonic system into a Pacific tectonic system. The Early and Middle Jurassic was the beginning of the Pacific system and the period of the extinction of the ancient Asian system, and on the basis of long-term uplift and denudation, the Erlian Basin underwent inversion and thrust along the Indosinian land such as the Hegen Mountains and the Xilamulun River in the Nee or near EW direction, and then the basement was demolished and subsided.

The roots of the mountains disappear, the crust thins, and basins appear to accept sedimentation. Figure 2-16 shows the mountain-basin transformation model of the Erlian Basin.

Figure 2-16 Mountain-basin transformation model in Erlian Basin.

As can be seen from Figure 2-16, when ft

At fg0, the extrusion in the area is strong, resulting in the formation of a large number of thrust faults (Fig. 2-16(a)) and stratum denudation. When ft

Under the action of gravity, some reverse faults are reversed, the upper wall begins to decline, the denudation becomes weaker, and some low-lying places also appear sedimentary accumulation. When ft

Under the action of gravity, all the reverse faults are reversed and replaced by normal faults, and the area extends to both sides, and tension appears, forming a rift basin and depositing a large amount of accumulation.

Figure 2-17 shows the stress state patterns of extrusion basin and extensional basin. It can be seen from the figure that before the Jurassic, the basin was under the paleo-Asian tectonic system, and the convergence of the Sino-Korean plate and the Siberian plate formed the extrusion-type tectonic track of the Erlian Basin. At the beginning of the Jurassic, the tectonic system was transformed into the Pacific system, and the Erlian Basin was in an extensional state, forming an extensional basin dominated by the Early Cretaceous since the Jurassic.

Figure 2-17 Mechanical explanation of the formation and evolution of the Erlian Basin.

The early evolution of the Erlian Basin was the gradual eastward migration of the Pacific plate subduction, resulting in the continuous eastward creep, expansion and accretion of the ancient Asian continent, so the shallow extensional basin migrated from west to east, and the development peaks of the Erlian Basin, Songliao Basin and Yi-Shu Graben were Late Jurassic-Early Cretaceous, Early Cretaceous, and Paleogene-Neogene, respectively (Fig. 2-18).

Fig. 2-18 Dynamic model of basin formation in Erlian Basin and Northeast Asia (modified according to Du Xudong et al., 1999).

Regardless of the type of basin, it is done by sedimentation. That is to say, basins are formed by the sedimentary material transported by rivers to settle in lakes, and then form marshes, wetlands, sedimentary plains, and sedimentary basins.

Further explanation, lake sedimentation, can form alluvial plains, sedimentary plains, and sedimentary plains, but it covers all the sedimentary areas, just because the size of the area is different, divided into sedimentary plains, sedimentary basins, sedimentary marshes, sedimentary wetlands, sedimentary areas, and according to the size of the sedimentary area, as well as the geomorphological structure around the sedimentary area, there is a sedimentary plain, if the area of this sedimentary plain is relatively small, and the surrounding area is high, then, this is a sedimentary basin. From this point of view, we can see the true origin of the basin thoroughly. -- No matter what kind of basin it is, it is the product of sedimentation.

Take the Sichuan Basin as an example, at first, the Sichuan Basin was a water area, according to the lowest average sedimentation rate, 1cm a year, the average depth of this lake in the Sichuan Basin is 50 meters, then, the sedimentation of the Sichuan Basin this water, through calculation, it will take about 5000 years, the data will not lie.

Basins are mainly formed due to crustal movements. Under the action of crustal movement, the underground rock layer is squeezed or stretched, and becomes bent or fractured, which causes some parts of the rock to uplift and some parts to fall, such as the descending part is surrounded by those parts of the uplift, and the rudiments of the basin are formed.

Many basins have been flooded by seawater or lakes since they were formed, such as the Sichuan Basin, the Tarim Basin, and the Junggar Basin. Later, as the earth's crust continued to rise and sediment accumulated, the sea and lakes in the basin slowly retreated and dried up, leaving only some rivers or streams. However, in those seas, lakes and rivers that once existed, a large number of organisms that once lived were buried in the silt after death, which will become the material basis for the formation of oil and coal, which is an important reason why scientists pay great attention to basin research.

Most of the rock deposits in the basin are relatively intact and continue to be marketed, and the animals and plants living there are also relatively easy to preserve into fossils after death, so the basin is also a good place for paleontologists to find fossils.

There are also some basins, which are mainly formed by the destruction of external forces on the surface, such as wind and rain. Rivers erode and cut down along the rocky deficit areas of the earth's surface, forming valley basins of various sizes. In the vast arid areas of northwest China, the wind is particularly strong, and after blowing away the sand and gravel on the surface, a saucer-shaped wind erosion basin is formed.

Some basins in regions such as Gansu, Inner Mongolia and Xinjiang were formed in this way.

In addition, in some areas where limestone is developed underground, the perennial flow of groundwater will cause the rocks there to dissolve, causing the surface rocks to collapse, and also forming basins, which geologists call karst basins. There are many basins of this type in southwest China, such as the Yunnan-Guizhou Plateau and Guangxi.

Under the strong extrusion or stretching action, the basement of some large basins with pants will be fractured, forming some "fault basins", which are more common in areas with severe crustal activity such as the Bohai Bay in North China and the Hengduan Mountains in Southwest China.

Sedimentary basins are often affected by tectonic activities in the crust during their development, and this activity can be recorded by the sediments that the basin has received continuously, and through the geological and geochemical study of these sediments, one can describe and reversely describe and reversely the historical processes of the Earth's evolution in these regions, such as climate change, sea level changes, the exchange of greenhouse gases that have a significant impact on the climate and the atmosphere, and topographic changes determined by tectonic activities.

The long-term sedimentation of the lake will form a lacustrine plain, and the formed lacustrine plain does contain a lacustrine basin. [covers face].

There are many famous basins in our country, so do you know how basins are formed?

How the basin was formedThe basin is high on all sides and low in the middle, and the whole terrain resembles a large basin. The basin is generally surrounded by plateaus or mountains, and the central part is plains or hills.

There are two main types of basins: one is the basin formed by the tectonic movement of the earth's crust, which is called the tectonic basin, such as the Turpan Basin and the Jianghan Plain Basin in Xinjiang, China; The other is the basin formed by the erosion of glaciers, flowing water, wind and karst erosion, which is called erosion basin, such as the Jinghong Basin in Xishuangbanna, Yunnan Province, China, which is mainly formed by the erosion and expansion of the Lancang River and its tributaries.

The basin area varies in size, and China's Sichuan, Tarim, Junggar and Qaidam basins are all more than 100,000 square kilometers. The small basin is only a few kilometers in circumference, and is called "dam" in Guizhou. In some basins, the natural conditions are superior and the resources are abundant, and they are called "cornucopias".

The basin topography is copied on the basis of raiding.

Lakes and water areas, lakes and water areas have sedimentation rates, and with the passage of time, the bottom of the lake increases, forming marshland, and then evolving into land, because the land formed in the lake basin has the same land structure as the basin, therefore, the formation trajectory of the basin appears, lake waters, marshland, land, basins.

1. Beneficial effects:

1) The clouds over the basin are usually thicker than those on the plateau, so the ultraviolet rays are not very strong, and the sunlight is more gentle, which is beneficial to people's maintenance.

2) The humidity of the basin is usually greater than that of the plateau, which is beneficial to the cultivation of some crops or flowers, and is also beneficial to the maintenance of people when it is in the middle of the rise.

3) From the topography of the basin, it is surrounded by high terrain on all sides, so it is relatively safer from the political and military aspects.

4) From the perspective of geological structure, the basin is usually relatively stable, and there are fewer disasters.

5) There is often more fertile soil in the basin than the outside, which is conducive to the development of agriculture.

2. Adverse effects:

1) Because of its high terrain on all sides, the basin generally has great restrictions on the development of transportation, and foreign exchanges are not as convenient as the plains.

2) The basin has less solar radiation due to its thicker cloud layer, which is not conducive to the utilization of solar energy.

3) Summer is more sultry than plateaus and plains because of its strong atmospheric inverse radiation and stronger thermal insulation effect.