No. 5] Proc. Japan Acad., 60, Ser. B (1984) 103

28. The History of the Eastern Wing of the Mongolian Geosyncline

By Teiichi KoBAYASHi, M. J. A. (Communicated,May 12, 1984)

In 1931 when Grabau published "The of Mongolia" including the copious faunas of Jisu Honguer and Sairu Usu, I described some late Palaeozoic shells from Soron on the eastern side of the Great Khingan range. Little was known of older Palaeozoic record of his Mongolian geosyncline at that time. Since then to Permian fossils were discovered at various places in central and north Manchuria i.e. Northeast China. Therefore I proposed with Nakano in 1942 the Manmo supergroup for the series of sediments in the geosyncline and discussed the Akiyoshi orogenic cycle in the Mongolian geosyncline in this journal, vol. 18. Still later in 1971 I carried out a synthetic study on the geosyncline to the east of the longitude through Uran Bator, in gathering new facts in Northeast China and the neighbouring areas, including the Redlichia-bearing Bystinsk limestone and dolomite in Transbaikalia and the Buyan- kovskaya series with Lower and Middle archaeocyathids of the Hanka area, South Primorye, USSR. Recently Lenaian archaeocyathids were found in Northeast China at Yiershi in northwest Kirin province, Middle Cambrian trilobites near Yichun and Upper Cambrian brachiopods at some places in Heilongj fang. Arenigian and later trilobites, graptolites and other fossils occur in places in the Great and Lesser Khingan ranges. Of the later Palaeozoic biostratigraphy Llandovery-Taranon graptolite zones were discriminated in the Taoshan series near Zhangchun and Middle and Upper Silurian shelly facies is well de- veloped not only at Erdaogou, Yongji, but also in Suifung area, Kirin province. The Wangj iaj ie series in central Kirin yields Middle corals and brachiopods. On the northwest side of Hanka lake there is the Middle Devonian Heitai formation at Mishan and beyond the international boundary there is the Calymena bearing Korodonka formation in Primorye. These Silurian and Devonian formations are rich in volcanic and pyroclastic materials. Hamada (1971) described 20 species of brachiopods Siegenian-Emsi.an in age from the Houlungmen for- mation in the northern highland of Heilongj iang. It contains also 104 T. KOBAYASHI [Vol. 60(B),

Phacops manchuricvs and Odontochile sp. (Kobayashi and Hamada, 1977) . The best display of the Devonian system in Northeast China is found in the northern part of the Great Khingan range where the Famennian Clymenia limestone exists in the upper Taminshan formation. The system of Kirin consists of shale and sand- stone, partly tuffaceous, and with intercalation of limestone layers and lenses represents the best sequence in Northeast China which is divided into the Beitongqigou, Lujuantun, Mopanshan and Shijuzi series in ascending order, all fossiliferous and rich in fusulinids, corals and brachiopods. The Lower Permian in Heilongj fang consists of the Gaoj iwo- peng, Sijiashan and Liutiaogou series, over 4,000 m in total thickness. Besides limestone and clastics acidic and intermediate volcanics are contained in the lower and upper series. All of the three yield fusulinids and other marine fossils. On the east side of the Great Khingan range Middle or early Upper Permian marine shells occur at Soron and Upper Permian naiads somewhat related to the Kol- chugino fauna of the Kuznetsk basin at the Hahai bank in adjacence. The naiads are widely distributed to Aif ui in the north and Kirin in the south, showing the extensive marine regression in the late Permian epoch. In the Yichun-Yuquan area, eastern Heilongj fang the Sanjiaoshan series composed of slate and porphyrite yields Comia and other plants of the Angara flora. In the overlying Wudaoling series acidic-intermediate volcanic rocks and their pyroclastics are chief components. The Hongshan series at the top consists of sandstone, conglomerate and shale and contain the Angara flora and Hahai naiads. As stated above, the Manmo supergroup comprises volcanic and pyroclastic rocks in many parts of its sequence showing repeated intrageosynclinal volcanism. Much is, however, not known of the stratigraphic relation among the Silurian and older rocks, although the Silurian formation overlies the Ordovician near Mt. Tabun Hara Obo in Mongolia and the Pre-Cambrian crystalline schists on the Nora river in the Zeya basin. The Devonian formation overlies the older strata with strong discordance at Chinshuei, northern Manchurian highland and also along the Argun river. In the Great Khingan range the Suhuho formation containing Cardiograpt2ts and other Ordovician fossils is overlain by the Devonian formation unconf ormably. In the upper Amur valley the Lower Carboniferous Tiparani formation of the Oldoi tributary discordantly overlies the Silurian and Devonian for- mations. Likewise the Carboniferous lies on the Silurian rocks in No. 5] Eastern Wing of Mongolian Geosyncline 105 the Panshih district near Kirin. In the southwestern side of the Great Khingan range the Lower Permian West Uj imuchin formation which is the correlative to the Jisu Honguer formation is separated from the Middle Permian Dabussumnor formation with strong dis- cordance and conglomerate is well developed in the latter. In Trans- baikalia the Kazanian formation containing the boreal fauna begins with the basal conglomerate on the older rocks. These discordances as a whole indicate crustal movements during the prolonged Palaeo- zoic era and at length the geosyncline turned out land in the late Permian age, leaving Transbaikalia and Ussuri where the early sea ingressed. Four species of Carnia recently discovered at Jiutai near Changchun are a sole limnic fauna in the dry land of Northeast China in the age. The Palaeozoic history of the so-called Koreo-Chinese massif or heterogen in which the Sinian and later sediments are extensive is quite different from the Mongolian geosyncline. There the Cambro- Ordovician Chosen or Korean group and the Heian or Pheongan group from Moscovian to early Triassic are separated by para- unconformity indicating the long middle Palaeozoic land period. Volcanic materials are quite scarce or absent in these supergroups and also the underlying Sinian or Shogen supergroup. The northern boundary between the heterogen and geosyncline extends through Tatientzu, Hueinan and Huatien and further to the east, but it is suddenly bent to the south and runs into Korea between the Kaema plateau and the Touman area in her extreme northeast. The Permo-Carboniferous granites are extensive in the central and northern parts of Northwest China and the Chuchtuinsk granite in Mongolia belongs to the same plutonism. The Mongolian orogen was united with the Koreo-Chinese heterogen by the Permo-Triassic Akiyoshi orogeny and related granitization.

References`) Grabau, A. W. (1931) : The Permian of Mongolia. Natural History of Central Asia. vol. 4, 665 pp. Kobayashi, T. (1931) : Upper Palaeozoic shells of Soron in the Great Khingan range. Japan. J. Geol. Geogr., 8, 241-250, pl. 24. --- (1942a) : The Akiyoshi orogenic cycle in the Mongolian geosyncline. Proc. Imp. Acad., 18, 306-313. (1942b) : The Sakawa orogenic cycle in the Amur geosyncline. ibid., 18, 314-316. (1971) : The Manmo group of the Mongolian geosyncline in Manchuria and adjacent areas. Geology and Mineral Resources of the Far East. vol. 3. Univ. of Tokyo Press, pp. 3-69. `' An extensive bibliography is appended to Kobayashi (1971) and later references will be compiled in another paper now in preparation.