Zanda basin

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The Zandabecken , in the scientific literature especially in the English name as Zanda Basin or Zhada Basin known one is tectonic sedimentary basin on the northern edge of the Himalayas in the circle Zanda , District Ngari , and in the far west of the Tibet Autonomous Region in the People's Republic of China .

The basin was created by a tectonic plate shift in connection with the mountain formation of the Himalayas ( pull-apart sag basin ) and was then filled up by sedimentation . It is mainly known as a fossil deposit , among the finds are numerous fossils of vertebrates from the late Miocene to the early Pleistocene and thus spanned the entire period of the Pliocene about 5.3 to 2.6 million years ago.

Geographical location

The Zanda Basin is located in the southwest of the Tibetan Highlands , north of the main Himalayan ridge . In the northeast, the Ayilariju Mountains form the natural border. It runs parallel to the main axis of the Himalayas from northwest to southeast and is around 100 km long and around 30 km wide. The Zanda Basin is traversed from east to west by the Satluj River (called Langqên Zangbo or Xiàngquán Hé here), which drains south-west towards the Punjab after leaving the basin and later flows into the Indus . The river cuts deep into the deposits, down to the marine deposits of the former Tethys Ocean , which form the basis of the highlands and date to the Mesozoic . This erosive activity of the river leads to the good outcrop conditions in the Zanda Basin. The Zanda Basin was created by tectonic movements of the subsurface when the Himalayas unfolded. As a result, the basin is framed by numerous tectonic fault zones. The South Tibetan Detachment System , one of the main folds of the high mountains, is of particular importance in the south . Due to these tectonic movements, the Zanda Basin is now at an altitude of between 3700 and 4500 m above sea level. This extreme altitude creates a generally cold climate with an average annual temperature of 0 ° C. The summers are mostly dry and the winters are wet compared to the eastern Himalayas.

Geology and paleontology

Location of the district of Zanda (pink) in the administrative district of Ngari (yellow)

The zanda basin contains a total of 800 meters high layer of fine to coarse-grained sediments, in which there are numerous fossils. Due to many finds of well-preserved vertebrate fossils, especially fish and mammals, it is an important fossil deposit from the late Miocene to the early Pleistocene . Due to the location of the basin and the history of the fossils, the fauna of the area can be reconstructed and interpreted during the Pliocene period. During the documented period of time, the highlands of Tibet , which arose in the course of the formation of the Himalayas in the early Miocene, dried up , as well as the almost complete glaciation of the highlands at the beginning of the Pleistocene Ice Age and the associated increase in monsoon activities in India and East Asia.

Biostratigraphy and Zoogeography

A large-scale research company of the Chinese Academy of Sciences in the Zanda Basin has been able to document the time since 2006 and work out a detailed biostratigraphy on the basis of mammalian fossils found from a total of 240 vertebrate sites. The lowest layer, 150 meters thick, was assigned to the late Miocene era 6.4 to 5.3 million years ago, and mammalian fossils in this area belong to the genera Ochotona , Panthera , Qurliqnoria , Palaeotragus and Hipparion . This layer is followed by the layer assigned to the Pliocene (150 to 620 meters) with small mammals such as Prosiphneus , Mimomys , Apodemus and Trischizolagus as well as numerous large mammals such as Coelodonta thibetana , Hipparion zandaense , Chasmaporthetes , Nyctereutes , Meles and Antilospira . The top layer (620 to 800 meters) contains only a few fossils that are characteristic of the Pleistocene, including horses ( Equus ).

The zoogeographical composition of the fossil and recent mammal fauna is traced back to a mosaic of species and genera, which on the one hand belong to the typical fauna of East Asia and above all northern China, and on the other hand have their origin in the Tibetan highlands. The species of the latter group include, among other things , various species of the piphare , the extinct squirrel genus Aepyosciurus and the Qurliqnoria , an early relative of the modern Tibetan antelope ( Pantholops hodgsonii ).

“Out of Tibet” hypothesis

The findings of various mammals, especially the find of the rhinoceros Coelodonta thibetana , an ancestor of the woolly rhinoceros that was widespread during the Ice Age , led to the formulation of the “out-of-Tibet” hypothesis. According to this theory, numerous adaptations of various mammals to life in cold regions occurred during the Ice Age in the highlands of Tibet. These species then spread over the ice age-affected area of ​​the northern hemisphere. The hypothesis was reinforced by other fossils, including the first description of the fox Vulpes qiuzhudingi , fossils of the Panthera blytheae , an early big cat species, and the oldest fossils of the genus Sinicuon , a close relative of the red dog .

Research history

The first major investigations began with the discovery of a right upper jaw fragment with heavily chewed teeth of the extinct giraffe Palaeotragus , which was made during an expedition of the Chinese Academy of Sciences in 1976 at an altitude of over 4000 m. Further finds were made in the years, including the remains of the horse Hipparion and a molar of a rhinoceros. At the beginning of the third millennium, the first fossils of a pika from the genus Ochotona were added in the form of two premolars. Intensive field research took place almost annually between 2006 and 2012. Among other things, the skull of the early woolly rhinoceros Coelodonta thibetana , another skull of the big cat Panthera blytheae and the remains of the jaw of the fox Vulpes qiuzhudingi and another dog representative, Sinicuon dubius , were discovered. In several cases, these are predecessor forms of mammals, which later in the course of the Pleistocene and partly still today occupy a dominant position in the northern regions of Eurasia, which led to the formulation of the "out-of-Tibet" hypothesis. In addition to the large mammals and fish, that is scattered throughout the sediment sequence with the exception of the uppermost and lowest areas, two sites with remains of small mammals were discovered at the base of the sequence, which enable an exact biostratigraphic age classification of the finds from the zanda basin. The research in the Zanda Basin continues to this day.

literature

  • Xiaoming Wang, Qiang Li, Guangpu Xie, Joel E. Saylor, Zhijie J. Tseng, Gary T. Takeuchi, Tao Deng, Yang Wang, Sukuan Hou, Juan Liu, Chunfu Zhang, Ning Wang, Feixiang Wu: Mio-Pleistocene Zanda Basin biostratigraphy and geochronology, pre-Ice Age fauna, and mammalian evolution in western Himalaya. Palaeogeography, Palaeoclimatology, Palaeoecology 374, 2013; Pp. 81-95. doi : 10.1016 / j.palaeo.2013.01.007

supporting documents

  1. ↑ a b c d e f g Xiaoming Wang, Qiang Li, Guangpu Xie, Joel E. Saylor, Zhijie J. Tseng, Gary T. Takeuchi, Tao Deng, Yang Wang, Sukuan Hou, Juan Liu, Chunfu Zhang, Ning Wang, Feixiang Wu: Mio-Pleistocene Zanda Basin biostratigraphy and geochronology, pre-Ice Age fauna, and mammalian evolution in western Himalaya. Palaeogeography, Palaeoclimatology, Palaeoecology 374, 2013; Pp. 81-95. doi : 10.1016 / j.palaeo.2013.01.007
  2. ↑ a b Qingsong Zhang, Fubao Wang, Hongxiang Ji and Wanpo Huang: Pliocene Sediments of the Zanda Basin, Tibet. Journal of Stratigraphy 5 (3), 1981, pp. 216-220
  3. ↑ a b Xiaoming Wang, Qiang Li, Zhu-Ding Qiu, Ban-Yue Wang, Zhan-Xiang Qiu, Zhijie J. Tseng, Gary T. Takeuchi, Tao Deng: Neogene Mammalian Biostratigraphy and Geochronology of the Tibetan Plateau. In: Xiaoming Wang, Lawrence J. Flynn and Mikael Fortelius (Eds.): Fossil Mammals of Asia. Neogene Biostratigraphy amnd Chronology. Columbia University Press, New York, 2013, pp. 274-293
  4. ↑ a b Tao Deng, Xiaoming Wang, Mikael Fortelius, Qiang Li, Yang Wang, Zhijie J. Tseng, Gary T. Takeuchi, Joel E. Saylor, Laura K. Säilä, Guangpu Xie: Out of Tibet: Pliocene Woolly Rhino Suggests High -Plateau Origin of Ice Age Megaherbivores . In: Science 333, September 2011, pp. 1285-1288. doi : 10.1126 / science.1206594
  5. ↑ a b Xiaoming Wang, Zhijie Jack Tseng, Qiang Li, Gary T. Takeuchi, Guangpu Xie: From 'third pole' to north pole: a Himalayan origin for the arctic fox . In: Royal Society (ed.): Proceedings of the Royal Society B . 281, No. 1787, June 11, 2014. doi : 10.1098 / rspb.2014.0893 . Retrieved July 8, 2014.
  6. ^ A b Z. Jack Tseng, Xiaoming Wang, Graham J. Slater, Gary T. Takeuchi, Qiang Li, Juan Liu, Guangpu Xie: Himalayan fossils of the oldest known pantherine establish ancient origin of big cats. Proceedings of the Royal Society B - Biological Sciences vol. 281 no. 1774 20132686, November 2013. doi : 10.1098 / rspb.2013.2686
  7. ↑ a b Xiaoming Wang, Qiang Li, Guangpu Xie: Earliest record of Sinicuon in Zanda Basin, southern Tibet and implications for hypercarnivores in cold environments. Quaternary International, in Press 2014 (available online since March 2014). doi : 10.1016 / j.quaint.2014.03.028
  8. ↑ Meng Xiangang, Zhu Dagang, Shao Zhaogamg, Yang Chaobin, Han Jian'en, Yu Jia, Meng Qingwei: Discovery of fossil teeth of PlioceneOchotonain the Zanda Basin, Ngari, Tibet, China. Geological Bulletin of China 24, 2005, pp. 1175-1178