Characteristics of China's Four great basin

Great basin: Tarim Basin in the south of Xinjiang Uygur Autonomous Region, Junggar Basin in the north, Sichuan Basin and Qaidam Basin in the northwest of Qinghai.

(1) Tarim basin

It is the largest inland basin in China, located between Tianshan and Kunlun Mountains. The widest point from north to south is 520km, and the longest point from east to west is 1, 400km. It covers an area of more than 400,000 square kilometers.

Tarim basin is a large-scale closed intermountain basin, and it is a stable block limited by many deep and large faults in geological structure. The basement of this block is paleocrystalline rock, on which there are Paleozoic and Proterozoic sedimentary caprocks with a thickness of about 1000 meters, as well as thinner Mesozoic and Cenozoic sediments, and there are large areas of Quaternary sediments. The topography of the basin is high in the west and low in the east, with a slight inclination to the north. Old Lop Nur is 780 meters above sea level, which is the lowest point in the basin. Tarim River is located in the northern margin of the basin, and the water flows eastward.

(2) Junggar basin

Northern Xinjiang. The basin is an irregular triangle with high east and low west. The central part of the basin is a vast desert, which is affected by the humid air flow from the ocean, with a little more precipitation in the northwest. The pasture in the basin is vast, the animal husbandry is developed, and the oasis and reclamation agriculture are also quite large.

Junggar basin is located between Altai Mountain and Tianshan Mountain, with the western hills of Junggar in the west and the foothills of Beita Mountain in the east. It is 450 kilometers wide from north to south and 700 kilometers long from east to west, covering an area of 6.5438+0.8 million square kilometers, with desert accounting for 30%. The terrain is inclined to the west, and the north is slightly higher than the south. Lake Ulungu (Bulento Sea) in the north is 479.438+0m above sea level, Lake Manas in the middle is 270m above sea level, and Lake Ebinur in the southwest is 65.438+089m above sea level, which is the lowest point in the basin. There are several gaps in the west side of the basin, such as Irtysh River Valley, Emin River Valley and Alashankou. The westerly airflow enters through the gap, bringing precipitation to the basin and surrounding mountains.

(3) Qaidam basin

It is one of the three inland basins in China, and it is a huge closed intermountain fault basin. Located in the northwest of Qinghai Province. Surrounded by Kunlun Mountain, Qilian Mountain and Altun Mountain, it covers an area of about 250,000 square kilometers. "Qaidam" is a Mongolian language, which means "salt ze"

. Qaidam basin belongs to plateau continental climate, and drought is its main feature. The annual precipitation decreases from 200mm in the southeast to 15mm in the northwest, and the annual average relative humidity is 30% ~ 40%, and the lowest can be lower than 5%. The annual average temperature in the basin is below 5℃, and the temperature changes dramatically. The annual absolute temperature difference can reach above 60℃, the daily temperature difference is often around 30℃, and it can drop below 0℃ at night in summer. The wind is strong, and the number of gale days above magnitude 8 can reach 25 ~ 75 days, and there can even be a gale of 40 meters per second in the west, which is highly erosive.

(4) Sichuan Basin

It is a famous red bed basin in China, with the most typical shape, the southernmost latitude and the lowest elevation in the great basin of China. Located in the east of Sichuan Province, on the upper reaches of the Yangtze River, it covers an area of more than 260,000 square kilometers, accounting for 46% of the area of Sichuan Province. Sichuan Basin borders Qinghai-Tibet Plateau and Hengduan Mountains in the west, Qinling Mountains in the north, Loess Plateau in the east and Yunnan-Guizhou Plateau in the south. There are many low mountains and Zhongshan mountains on the edge of the basin, and the mountains are steep. Most of the rivers in the mountains on the edge of the basin are V-shaped valleys with a height difference of more than 500 ~ 1 000 meters, and the surface is rugged, so there is a saying in history that it is difficult to get through the Shu Road and get into the sky. Karst landforms such as stone forest, karst cave, underground river and valley can be seen in limestone distribution area. Xingwen County in the southern margin of the basin is known as "Shilin Cave Township". Famous mountains such as Twelve Peaks in Wushan and Jinfo Mountain are also mainly developed from limestone. Emei Mountain, which is composed of limestone, basalt and granite, and Qingcheng Mountain, which is composed of sandstone, mudstone and conglomerate, is known as "Emei is beautiful on earth" and "Qingcheng is quiet on earth", and is a famous tourist attraction in China.