Characteristics of Qaidam Basin

Qaidam basin is a "lowland" in the northern part of Qinghai-Tibet Plateau. It is an equilateral triangle with an altitude of 2600-3000m. The climate in the basin is extremely dry, and special external forces have great influence on the formation of basin landforms. The Qaidam Basin is surrounded by mountains. Before the middle tertiary (40 million years ago), it was a big lake. After that, the lake gradually shrank and dried up, so that a lot of salt and gypsum were accumulated.

The western Qaidam basin is a moderate uplift area in neotectonic movement. The water system is centripetal, and all rivers are submerged as soon as they leave the mountain pass, forming an undercurrent and flowing into the lake basin. Lake plains are widely distributed, with large salt marshes and saline soil. Extending from the lake basin to the periphery, it is a flat alluvial plain. A gently inclined piedmont flood plain with a width of 10-20k m is widely developed between the edge of the foothills and the western hills, which is mainly composed of Quaternary flood gravel and sand layers. The Tertiary strata in the northwest of Qaidam Basin are mainly loose mudstone and sandstone, and the structural strike is consistent with the dominant wind direction. Under the strong wind erosion, ridge-shaped wind erosion hills and wind erosion wasteland arranged roughly parallel to the main wind direction are formed. The former is 10-20 meters higher than the former, and some of them reach 40-50 meters, with lengths ranging from 10- 100 meters. There are a series of mountains parallel to Qilian Mountain in the north of Qaidam Basin, with a relative height difference of about 500 meters. There are small intermountain basins such as Dachaidan and Xiaochaidan with one or several lakes as the center between mountains, and there are lakeside, lacustrine plain and alluvial-diluvial inclined plain. In mountainous areas, gullies are particularly developed, and some mountain sections have been divided into discrete island hills, with thick debris accumulation under the hillside. The southeast of Qaidam basin is a long-term crustal subsidence area with flat ground, concentrated water sources and large lake area. Marshes are widely distributed, and alluvial plains are mostly gravel and sand mounds, and the surface is mostly rugged and hard-shelled saline soil.