Genesis of Chengdu Plain

One of the largest plains and dense river networks in southwest China is also the largest producer of mirabilite in China. Also known as Penxiping Plain or West Sichuan Plain. Located in the west of Sichuan Basin. Chengdu Plain in a broad sense is located between Longquan Mountain, Longmen Mountain and Qionglai Mountain, with oil near the river in the north and Wu Tong Bridge in Leshan in the south. Including Mianyang, Jiangyou and Anxian alluvial plains in the north, Minjiang and Tuojiang alluvial plains in the middle, Qingyijiang and Dadu River alluvial plains in the south. There are hills and plateaus between the three plains, with a total area of 23,000 square kilometers. In a narrow sense, Chengdu Plain only refers to the Minjiang River and Tuojiang River alluvial plains bounded by guanxian, Mianzhu, Luojiang, Jintang, Xinjin and Qionglai, covering an area of 8,000 square kilometers, which is the main part of the western basin plain. Because Chengdu is located in the middle of the plain, it is called Chengdu Plain.

Chengdu Plain is developed on the basis of the northeast-southwest syncline structure, and it is a composite alluvial fan plain composed of eight alluvial fans such as Minjiang River, Tuojiang River (Mianyuan River, Shiting River and Juanjiang River) and their tributaries. The loose sediments on the surface of the whole plain are extremely thick, and the Quaternary sediments are covered with silt and clay, with good structure and suitable for farming. It is the most fertile soil area in Sichuan Province, with an altitude of 450-750 meters, flat terrain, slightly inclined from northwest to southeast, with an average slope of only 3- 10 ‰ and a relative elevation difference below 20 meters, which is conducive to the development of gravity irrigation. As early as 250 BC, the world-famous Dujiangyan Water Conservancy Project was built in the Qin Dynasty, which led the Minjiang River to irrigate a large area of farmland on the plain and became one of the earliest areas in Sichuan Province. After continuous reconstruction and expansion, the irrigation area of Dujiangyan has been greatly expanded compared with the early 1950s, and the irrigation area has increased by three times. Irrigation and water conservancy is very developed, and cultivated land is concentrated and contiguous. It belongs to a typical paddy field agricultural area, and the land utilization rate is as high as 60%. Crops mainly include rice, wheat and rape, with high and stable yield. The commodity grain and oil provided all the year round accounts for about 1/5 and 2/5 of Sichuan Province respectively. It is a famous commodity grain and oil production base in Sichuan and even the whole country. The level of pig raising ranks in the forefront of the province, and it is a pig raising base in Sichuan. However, because the plain is adjacent to the western Sichuan Plateau, it is deeply affected by the sinking of cold air in mountainous areas, and most of the river water in the plain comes from the melting water of snow and ice in the western plateau and mountainous areas. At the same time, in the low-lying ancient river area on the plain, the groundwater level is high and the soil is cold and wet. Therefore, the air temperature, water temperature and ground temperature in Chengdu Plain are low, and the thermal conditions are slightly worse than those in other areas of Sichuan Basin.