Qaidam Basin

''Tshwa'i 'Dam is the Wylie romanization of the Tibetan name , meaning "Salt Marsh"; the Tibetan Pinyin romanization of the same name is Caidam. Qaidam is the GNC romanization of its transcription into Mongolian; Tsaidam is a variant romanization of the same name. Chaidamu'' is the pinyin romanization of its transcription into Chinese characters; the same name was formerly romanized as the for the Chinese Postal Map. ==Geography==

Orographically, the Qaidam Basin is a comparatively low area in the northeastern part of the Qinghai–Tibet Plateau. With an elevation of around , Qaidam forms a kind of shelf between Tibet to the south (around ) and Gansu to the north (around ). 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 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. ==Geological history==

Qaidam was part of the North China Craton from at least 1 billion years ago, before breaking off million years ago at the end of the Neoproterozoic. It was an island in a shallow sea until uplift beginning around 400Ma finally rejoined it to the mainland by 200Ma. 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 shoreline somewhere between 55–35Ma. At first, Qaidam was at a far lower elevation. Pollen found in core samples 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. By 12Ma, the climate had dried enough to break Qaidam's single lake into separate basins, which frequently became saline. The basin's continuing formation and evolution is controlled by the Altyn Tagh fault constituting the northern basin boundary. ==Resources==

in SE Qaidam (2014). The two Taijinar lakes lie to the northwest and the lakes of the Qarhan Playa to the southeast. (ESA) 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 over 50 billion metric tons (55 billion short tons) of salt. Beneath the salt, Qaidam is one of China's nine most important petroliferous 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 refinery at Golmud, and the Sebei gas fields are connected to Xining, Lanzhou, and Yinchuan. Qaidam has reserves of asbestos, borax, gypsum, and several metals, with the greatest reserves of lithium, magnesium, potassium, and sodium found 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. Additional railroads spanning the basin include the Golmud–Dunhuang Railway completed in December 2019 and a 25 km private railway constructed by Zangge Mining Co., Ltd. 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. Construction began in November 2014 and concluded in 2020. ==References==