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Qaidam Basin

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The Qaidam, Tsaidam, or Chaidamu Basin is a hyperarid basin that occupies a large part of Haixi Prefecture in Qinghai Province, China. The basin covers an area of approximately 120,000 km2 (46,000 sq mi), one-fourth of which is covered by saline lakes and playas. Around one third of the basin, about 35,000 km2 (14,000 sq mi), is desert.

Qaidam is located in China
Qaidam
Qaidam
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Location of Qaidam in China
Qaidam Basin
Qaidam Basin
Chinese name
Traditional Chinese柴達木盆地
Simplified Chinese柴达木盆地
PostalZaidam Swamp
Literal meaningQaidam Lowlands
Transcriptions
Standard Mandarin
Hanyu PinyinCháidámù Péndì
Wade–GilesCh‘ai-ta-mu P‘en-ti
Tibetan name
Tibetanཚྭའི་འདམ་
Mongolian name
Mongolian CyrillicЦайдам
Qaidam Desert
Traditional Chinese柴達木盆地沙漠
Simplified Chinese柴达木盆地沙漠
Literal meaningQaidam Lowland Desert
Transcriptions
Standard Mandarin
Hanyu PinyinCháidámù Péndì Shāmò
Wade–GilesCh‘ai-ta-mu P‘en-ti Sha-mo

Name

Qaidam is a Tibetan name meaning "Salt Marsh". Tsaidam[1] is its transcription into Mongolian, and Chaidamu is the pinyin romanization of its transcription into Chinese characters. The same name was formerly romanized as the Zaidam Swamp for the Chinese Postal Map.[2]

Geography

Orographically, the Qaidam Basin is a comparatively low area in the northeastern part of the Tibetan Plateau.[3] With an elevation of around 3,000 m (10,000 ft), Qaidam forms a kind of shelf between Tibet to the south (around 4,300 m or 14,000 ft) and Gansu to the north (around 1,100 m or 3,500 ft). A low water divide separates the Qaidam Basin proper from that of Qinghai Lake to the east. Despite this lower elevation, Qaidam is still high enough that its mean annual temperature is 2–4 °C (36–39 °F)[4] despite lying on the same latitude as Algeria, Greece, and Virginia in the United States.

The crescent-shaped basin[5] covers an area of approximately 120,000 km2 (46,000 sq mi).[6][7] Its substrate is broadly divided into three blocks: the Mangya Depression, a northern fault zone, and the Sanhu Depression.[8] Qaidam is an intermontane basin, surrounded on all sides by mountain ranges.[3] 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 or Nanshan. In the northwest, the Altyn-Tagh separates it from the Kumtagh Desert of southeastern Xinjiang.

 
Yardangs in the Qaidam Desert.

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.[9] Across the entire basin, the mean annual rainfall is 26 mm (1 in) but the mean annual evaporation is 3,000–3,200 mm (120–130 in).[4] Because of the low rainfall, these lakes have become saline or dried up completely. Presently, there are four main playas in the basin: Qarhan in the southeast and (from north to south) Kunteyi, Chahanshilatu, and Dalangtan in the northwest.[9] These playas and a few other saline lakes occupy over one-fourth of the basin,[6] with the sediments deposited since the Jurassic as deep as 10[7] to 14 km[4] (6–9 mi) in places despite tectonic activity having repeatedly shifted the center of the region's sedimentation.[9] 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,[10] another reckoned 43 with a total area of 16,509 km2 (6,374 sq mi).[11]

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[12] for use in testing spectroscopy and equipment for China's 2020 Mars rover program.[13]

History

Map of West Qaidam 
Map of East Qaidam 
Detailed US Army maps of Qaidam, c. 1975. (Names given in Wade-Giles romanization.)

Qaidam was part of the North China Craton from at least 1 billion years ago, before breaking off c. 560 million years ago at the beginning of the Neopaleozoic.[5] It was an island in a shallow sea until uplift beginning around 400 Ma finally rejoined it to the mainland by 200 Ma.[5]

Three-dimensional modeling shows that the present basin has been squeezed to an irregular diamond shape since the beginning of the Cenozoic,[14] with the Indian Plate beginning to impact the ancient Tibetan shoreline somewhere between 55[15]–35 Ma.[16] At first, Qaidam was at a far lower elevation. Pollen found in core samples shows that the Oligocene (34–23 Ma) was relatively humid.[17] A great lake slowly formed in the western basin, which two major tectonic movements raised and cut off from its original sources of sediment.[17] At its greatest extent during the Miocene (23–5 Ma), this lake spread at the present 2,800 m (9,200 ft) elevation contour[6] over 300 km (190 mi)[4] 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.[18] The Tibetan plateau's uplift, however, eventually cut it off from the warm and humid Indian monsoon.[18] It went from a forest steppe to a desert.[5] By 12 Ma, the climate had dried enough to break Qaidam's single lake into separate basins, which frequently became saline.[4] During the Pliocene (5–2.5 Ma), the focus of most sedimentation was at what is now Kunteyi but, during the Pleistocene (after 2.5 Ma), tectonic activity shifted the basin's tributaries and floor, moving the focus of sedimentation from the Dalangtan to Qarhan area.[9] During this time, the record's glacial intervals suggest a low-temperature climate[17] and its sandstone yardangs attest to strong winds.[18]

From 770,000 and 30,000 years ago, the enormous lake which filled much of the southeastern basin alternated nine times between being a fresh- and saltwater lake.[19] At around 30 kya, this great—at the time, freshwater—lake spread over at least 25,000 km2 (9,700 sq mi) with a surface 50–60 m (160–200 ft) above the present levels of its successors. It was cut off and became saline again at that point and began precipitating salts about 25,000 years ago.[20] The basin's continuing formation and evolution is controlled by the Altyn Tagh fault constituting the northern basin boundary.[14]

Resources

 
A salt mine in the Qaidam Desert

The basin's large mineral deposits caused a great deal of investment interest from 2005. Qarhan Playa, a salt flat including about ten of the lakes, contains about sixty billion tons of salt.[citation needed] Beneath the salt, Qaidam is one of China's nine most important petroliferous basins.[21] There are 22 oil fields, with estimated reserves of 225 million tons, and 6 gas fields, holding 150 billion cubic meters of gas. It has reserves of asbestos, borax, gypsum, oil, and natural gas, and several metals, with the greatest reserves of lithium, magnesium, potassium, and sodium of anywhere in China.

Transportation

The Xining-Golmud rail line (the first stage of the Qinghai–Tibet Railway), which crossed the eastern part of the Qaidam Basin in the early 1980s, is an essential transportation link for accessing the region's mineral resources. As of 2012, additional rail lines are under construction. The construction of the Golmud–Dunhuang Railway started in October 2012; it is expected to be completed within 5 years.[22] In the early 2012, Zangge Potash Co Ltd started the construction of a 25-km private railway from the Qarhan station on the Qinghai–Tibet Railway (near the eponymous salt lake) to their facilities nearby.[23][24]

As of the late 2013, preliminary planning is conducted for the Golmud-Korla Railway, which will stretch along the entire western part of the Qaidam Basin as well.[25]

References

Citations

  1. ^ china.org.cn - Salt lakes
  2. ^ Stanford (1917), p. 21.
  3. ^ a b Meng & al. (2008), pp. 1–2.
  4. ^ a b c d e Warren (2016), p. 1104.
  5. ^ a b c d CNPC, p. 2.
  6. ^ a b c Chen & al. (1986).
  7. ^ a b Spencer & al. (1990), p. 395.
  8. ^ CNPC, p. 3.
  9. ^ a b c d Kong & al. (2018), §2.
  10. ^ Fan & al. (2012).
  11. ^ "About Salt Lakes", Official site, Qinghai Institute of Salt Lakes.
  12. ^ Kong & al. (2018), §1–2.
  13. ^ Kong & al. (2018), §4.
  14. ^ a b Guo & al. (2017).
  15. ^ Scotese (2001).
  16. ^ Aitchison & al. (2007).
  17. ^ a b c Mao & al. (2017), p. 48.
  18. ^ a b c Mao & al. (2017), p. 49.
  19. ^ Huang & al. (1997), p. 277.
  20. ^ Zheng (1997), p. 149.
  21. ^ CNPC, p. 1.
  22. ^ 格尔木至敦煌铁路开工 Archived December 9, 2012, at the Wayback Machine, Renmin Tielu Bao, 2012-10-20
  23. ^ 青海格尔木藏格钾肥有限公司铁路专用线项目开工 Archived February 21, 2012, at the Wayback Machine, 2012-02-18
  24. ^ China builds railway to benefit fertilizer supply, 2012-02-18
  25. ^ 库尔勒—格尔木铁路项目预可研报告获批 Archived October 22, 2013, at the Wayback Machine (Korla-Golmud Railway project preliminary feasibility study report approved), 中华铁道网, 2013-09-30

Bibliography

37°16′N 94°27′E / 37.267°N 94.450°E / 37.267; 94.450

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