Qaidam Basin

 ( Landforms Of Qinghai ) 

The crescent-shaped basin covers an area of approximately . Its substrate is broadly divided into three blocks: the Mangya Depression, a northern fault zone, and the Sanhu Depression. Qaidam is an intermontane basin, surrounded on all sides by mountain ranges. In the south, the Kunlun Mountains separate it from the higher central section of the Tibetan Plateau. In the north, a number of smaller ridges like the Shulenanshan separate it from another higher plateau, which usually referenced by the name of its northern escarpment, the Qilian Mountains or Nanshan. In the northwest, the Altyn-Tagh separates it from the Kumtagh Desert of southeastern Xinjiang.

Because of this position, Qaidam forms an endorheic basin accumulating lakes with no outlet to the sea. The area is among the most arid non-polar locations on Earth, with some places reporting an aridity index of 0.008–0.04. Across the entire basin, the mean annual rainfall is but the mean annual evaporation is . Because of the low rainfall, these lakes have become salinity or dried up completely. Presently, there are four main playas in the basin: Qarhan Playa in the southeast and (from north to south) Kunteyi Playa, Chahanshilatu, and Dalangtan Playa in the northwest. These playas and a few other occupy over one-fourth of the basin, with the sediments deposited since the Jurassic period as deep as 10 to 14 km (6–9mi) in places despite tectonic activity having repeatedly shifted the center of the region's sedimentation. The seasonal nature and commercial exploitation of some of the lakes makes an exact count problematic: one count reckoned there were 27 lakes in the basin,. another reckoned 43 with a total area of ..

The aridity, salinity, wide diurnal and seasonal temperature swings, and relatively high ultraviolet radiation has led to Qaidam being studied by the China Geological Survey as a Mars analogue for use in testing spectroscopy and equipment for China's 2020 Mars rover program.

Three-dimensional modeling shows that the present basin has been squeezed to an irregular diamond shape since the beginning of the Cenozoic, with the Indian Plate beginning to impact the ancient Tibetan Plateau shoreline somewhere between 55–35Ma. At first, Qaidam was at a far lower elevation. palynology found in shows that the Oligocene (34–23Ma) was relatively humid. A great lake slowly formed in the western basin, which two major tectonic movements raised and cut off from its original sources of sediment. At its greatest extent during the Miocene (23–5Ma), this lake spread at the present elevation contour over . and was among the largest lakes in the world. Nutrient-rich inflows contributed to plankton blooms, which supported an ecosystem that built up reserves of organic carbon. The Tibetan plateau's uplift, however, eventually cut it off from the warm and humid Indian monsoon. It went from a forest steppe to a desert ecology. By 12Ma, the climate had dried enough to break Qaidam's single lake into separate basins, which frequently became saline. During the Pliocene (5–2.5Ma), the focus of most sedimentation was at what is now Kunteyi Playa but, during the Pleistocene (after 2.5Ma), tectonic activity shifted the basin's tributaries and floor, moving the focus of sedimentation from the Dalangtan Playa to Qarhan Playa area. During this time, the record's suggest a low-temperature climate and its sandstone attest to strong winds.

From 770,000 and 30,000 years ago, the enormous lake which filled much of the southeastern basin alternated nine times between being a freshwater and saltwater lake. Palynology suggest the bed of Dabusun Lake in the Qarhan Playanearly the lowest point of the basinwas elevated about within the last 500,000 years. At around 30 kya, this greatat the time, freshwaterlake spread over at least with a surface above the present levels of its successors. At the same time, a river from the "Kunlun" paleolake to its south was enriching the Sanhu region with enormous reserves of lithium derived from near Mount Buka Daban which now feed into the Narin Gol River that flows into East Taijinar Lake.

Around 30 kya, the lake in the Kunluns dried up and the Qarhan was cut off from sufficient inflows of fresh water. It became saline again, beginning to precipitate salts about 25,000 years ago.. The basin's continuing formation and evolution is controlled by the Altyn Tagh fault constituting the northern basin boundary.

Beneath the salt, Qaidam is one of China's nine most important petroleum basins and its largest center of onshore production. The Qinghai Oilfield, exploited since 1954, includes the Lenghu, Gasikule, Yuejin-2, and Huatugou oil fields and the Sebei-1, Sebei-2, and Tainan gas fields. All together, it has proven reserves of 347.65 million metric tons (more than 2 billion barrels) of petroleum and 306.6 billion cubic meters (10.83 trillion cubic feet) of natural gas. Annual production capacity is about 2 million metric tons of petroleum and 8.5 billion cubic meters of natural gas. A pipeline connects the Huatugou field with a major oil refinery at Golmud, and the Sebei gas fields are connected to Xining, Lanzhou, and Yinchuan.

Qaidam has reserves of asbestos, borax, gypsum, and several , with the greatest reserves of lithium, magnesium, potassium, and sodium found anywhere in China.

The National Development and Reform Commission began conducting preliminary planning for the Golmud-Korla Railway in September 2013, which would stretch across the western portion of the Qaidam Basin. 库尔勒—格尔木铁路项目预可研报告获批 (Korla-Golmud Railway project preliminary feasibility study report approved), 中华铁道网, 2013-09-30 Construction began in November 2014 and concluded in 2020.

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• "Qaidam" in the Columbia Encyclopedia
• Qaidam Basin Photos from NASA