ISSN 1002-1027  CN 11-2952/G2

Acta scientiarum naturalium Universitatis Pekinensis

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Middle Ordovician Biogeography of Xing'anling-Mongolia-Northern Xinjiang and Adjacent Areas

MA Xueping   

  1. Department of Geology, Peking University, Beijing, 100871
  • Received:1996-11-07 Online:1997-07-20 Published:1997-07-20

Abstract: Synthetic analysis of 170 trilobite genera, 210 brachiopod genera, and 87 cephalopod genera leads to the recognition of two regions separated by the Irtys (river)-Sino-Mongolian boundary-Xar Molon (river)-Changchun line: the Middle Asia-East Asia region of the Proto-Pacific realmand the Northern Asia region of the Proto-Atlantic realm.The former is characterized by the trilobites Tangyaiinae and Hammatocnemiidae, and is closely related with the Australian and the Southern European regions in many aspects. For example, Cekovia and Pseudopetigurus are present both in the Middle Asia-East Asia region and in the Southern European region; Neseuretinus is present in all the above three regions; Pliomerina is widely distributed in the Middle Asia-East Asia region, in addition, it is also found in southeastern Australia. The Middle Asia-East Asia region is further subdivided into the North China, the Tarim, and the Kazakhstan provinces. The Kazakhstan province possesses many taxa that are also present in North America, South China, Tarim, and the Ordos area of North China, suggesting a transitional position between the two realms.The Ordos area of the North China province and the Tarim province are very similar statistically, probably due to similar environmental setting. Trilobite endemic ratios are usually low in various provinces (10%-15%), especially in marginal sea or deeper water facies.Cephalopods have a higher endemic ratio in the North China(30%) and Siberia (20%) provinces. Brachiopods are the most widely distributed and numerous in the study area, but their provincialism is quite indistinct.