106 Proc. Japan Acad., 60, Ser. B (1984) [Vol. 60(B), 29. The Amur Subgeosyncline and the Sungari Basin By Teiichi KOBAYASHI, M. J. A. (Communicated, May 12, 1984) Since Schonemann expressed the opinion in 1929 that the Mongol-Amur folded belt had been a geosyncline disturbed by the late Mesozoic orogeny, it was a moot discussion among Stille, Obrutschew and others. In 1942 I have pointed out in this journal, that the Mongolian geosyncline became a folded zone by the Permo-Triassic orogeny, but the Amur subgeosyncline was left behind the Mongoliden and later became a folded zone in the late Mesozoic period. Here I wish to elucidate the history in a further detail with reference to additional data gathered since then. In Northeast Mongolia the Triassic formation containing Ole- nekian ceratites and bivalves and early Keuper plants were found between the marine Upper Permian and the Lower Jurassic con- tinental formation in the Jargalatuin graben in the upper Onon tributary in Mongolia. The plant-bearing Lower Triassic overlies older granite near Chita. In the Lesser Khingan range the Triassic formation disconformably overlies the Upper Permian and yields marine shells from Induan to Ladinian. In Khetin and Vandan areas in the middle Amur valley there is no break from the f ossilif erous Middle and Lower Triassic formation to the Upper Permian for- mation. The Carnic to None formation containing Pseudomonotis over- lies Silurian and Devonian in the upper Amur and Permian and older rocks in east Tr,ansbaikalia with strong discordance. Its thickness attains 5,000 m. This is the molasse of the Ladinian orogeny corre- sponding to the Akiyoshi orogeny in Japan. While the Noric transgression was extensive, the Rhaetic emergence was also very wide in Eastern Asia, although Halorella was found in the Bureya tributary. Near Chabarowsk there is a good display of the Upper Palaeo- zoic formation containing Permian Spiri f er, f usulinids and others. In its southwest extension the Upper Permian to Middle Carboni- ferous f usulinids occur in the formation of Nandanhadaling. The Devonian Hetai formation exists at Mishan on the southeast side of the Wanda mountains. Asano correlated his Mashan metamorphic rocks near Shidao to the Proterozoic Liaoho group. Recently some Ediacaran fossils were reported by Liu Xiaoling (1981) from the No. 5] Amur Geosyncline and Sungari Basin 107 Lium.ao formation of the group near Lungshan. These formations constitute the Wantashan folded zone. These older rocks of the mountains are unconf ormably overlain by the Qingj fang group, 3,000 m thick, which is chiefly composed of tuff and diabase, but Pseudomonotis ochotica occurs in lower shale intercalation at Baoqing. Cycadocarpidium and other plants belong- ing to the Mine flora were found at Wangqing to the south near Korean frontier. These Upper Triassic sediments are the meta- orogenic molasse of the Middle Triassic movement in the Akiyoshi phase. In Transbaikalia the marine Jurassic sequence, some 2,700 m thick starts from the basal conglomerate. It is followed by the Aegoceras, Beaniceras and D~actyloceras zones, Aalenian and Bajocian shell beds and Callovian-Bathonian perisphincti in higher horizons. On the north side of the upper Gasimur there is the coal-bearing for- mation of Algachi, some 5,000 m thick, of which plants are nearer the Mongugai flora than the Nikan flora. Therefore the Algachi Jura is not younger than Middle Jurassic. The tuffaceous Mesozoic formations are distributed from the Turga to the south beyond the Argun river. They contain various conchostracans and other limnic fossils in some horizons in the range from Lower Cretaceous to Upper Jurassic or older. The Lycoptera- Ephemeropsis horizon is a key to Upper Jurassic. In the so-called Oldoy trough in the western upper Amur region the Jurassic formation, about 4,000 m, rich in bivalves is underlain by the Middle Palaeozoic rocks with angular unconformity. On the north side of the lower Argun the continental Jurassic formation called Kholodazhikan suite containing Middle Jurassic plants overlies the metamorphosed Middle Palaeozoic. Its upper part merges with the Bathonian-Callovian marine facies laterally. In the Bureya basin there are Mesozoic sediments, 7,000 m thick. Its lower part containing Bathonian-Callovian molluscs and belemnites is overlain by the coal-bearing Talyndzhan suite with local discordance. The Arctocephalites beds of the Longzhaogou group in eastern Heilongj fang indicate the Callovian marine ingression which has reached extreme Northeast China probably from the Bureya basin where A, orientalis occurs. In the lower Amur region the Lower Cretaceous formation con- tains Valangian-Albian Aucella and Aucellina. In the northern part of the region the formation 5,500 m thick is not so f ossilif erous as its correlative on the Sikhota Alin side and underlain by the Jurassic formation containing Upper Jurassic radiolarians. The Jurassic and Cretaceous formations of the Amur folded 108 T. KOBAYASHI [Vol. 60(B), zone may be divisible into the Aalenian and older part and the Oxf ordian (or Bathonian) and younger part by the Baj ocian emer- gence and related movements. While the upper part reveals the orogenic age, the lower part indicates the quiet or the true subgeo- synclinal age. The Mesozoic sea retreated in the late Cretaceous period from the Amur region. The Senonian or post-Udominsk orogeny was paroxysmal for the Sikhota Alin geosyncline. The Mongolian geosyncline suffered from the Permo-Triassic orogenies and related granitic intrusion. As the result the Mongoliden was fused with the Koreo-Chinese heterogen as far as Northeast China. The Amur subgeosyncline was left behind it and it migrated by itself beyond the Suif ung-Touman area to become the Sikhota Alin geosyncline. These secondary geosyncline and subgeosyncline became the folded mountains by the late Mesozoic orogenies. In the Penhsihu coal-field in the Taitzuho region in the heterogen the Pyeongan supergroup with the Lower Triassic Zhengjia forma- tion at the top is unconf ormably overlain by the Linj is formation containing Middle Triassic plants, fishes and insects. The next younger is the Cretaceous Tayu volcanic formation from which Plicatounio and Pinoxylon dakotensis were obtained. Hausmannia was collected at Tienshuaif ukou in the same region ; Cycadocarpidium at Wangqing. Upper Jurassic Lycoptera bearing beds are underlain by the Daedong plant beds unconformably near Sinuiju on the lower Yalu, North Korea. The Cornia beds of Jiutai are the sole sediments of the earlier Triassic age on the Mongoliden in Northeast China. The Upper Triassic-Lower Jurassic Daedong sediments are also scarce, but Asmussia khinganensis from Heitingshan on the east slope of the Great Khigan range belongs to the Daedong fauna. The Middle and Upper Jurassic formation is well developed in Jehol and particularly at Fushin. It is the correlative of the tuffaceous Jura of Turga and Witim containing the Lycoptera-Ephemeropsis fauna. The Upper Jurassic-Lower Cretaceous formation is scattered in Northeast China forming small basins. Onychiopsis elongata is reported from the coal-bearing of Fuchin and Haokang and from the oil-bearing of Tunning and Sanhsing; Trigonioides from Sanhsing and Talatzu; and Plicatounio from Pulantien, Yingpan and far north from the Zeya basin and Transbaikalia. It is a remarkable fact that boulder conglomerates occur in the late Jurassic-early Cretaceous formations at some places. For ex- ample, the Sunchiawan conglomerate, 1,400 m thick at Fushin con- tains boulders of 0.3 meter in diameter at the largest and uncon- f ormably overlies the above mentioned Jurassic formation . In the No. 5] Amur Geosyncline and Sungari Basin 109 Lunching area the Trigonioides bearing Talatzu series, 1,850 m thick with the basal conglomerate, 240 m thick is disconformably overlain by the Hualung coal-bearing, 1,150 m with the boulder conglomerate, 350 m thick at the base, and this in turn by the Hualung coal-bearing series yielding Onychiopsis and other plants unconformably. At the neck of the Laiotung peninsula the basal boulder conglomerate of the Pulantien formation overlies the Cambrian and Jurassic Wafang- tien formation which are strongly folded. Therefore it is certain that a great topographic change has taken place sometimes in the Jurassic- Cretaceous transition. In the Liao-Sungari plain the Sungari series which is least de- formed among the Mesozoic formations in Northeast China is widely distributed under the Quaternary blanket. In 1942, jointly with Suzuki, Takai and Huzita I have divided it into the Chuantou, Neng- kiang and Fulungchuan formations in ascending order and considered its major part to be middle and late Cretaceous, but the lower and upper limits may enter into Lower Cretaceous and Palaeogene. Re- cently the area was intensely investigated for oil-prospecting. As the result it is divided into six or more stratigraphic units, but various opinions are expressed for its division and age. Now it is certain that the lower limit extends as far as Lower Cretaceous, because Plicatounio occurs in the lower and middle parts. It is noteworthy that the Nengkiang formation became brackish by a temporary marine ingression where Mytilus, Brachidontes and Musculus occur. Because the Sikhota Alin geosyncline and the Amur subgeosyncline emerged in the late Cretaceous age, the Nengkiang formation must be pre-Senonian. The Fulungchuan formation defined in 1942 may be partly Palaeogene, because the Sungari correlative in the Zeya basin comprises the Plicatounio horizon in the lower part, Estherites posidonomyoides and Populus and other late Cretaceous plants occur near Kasatokina and the plants resembling the Laramie flora near Paschkov. The up and down movements in the early Cretaceous or near the end of the Jurassic period produced the large Sungari basin in Northeast China and the Tsushima basin between South Korea and West Japan and reciprocally Central and North Korea and East Manchuria as well as the Great Khingan range were elevated and supplied boulders to the intermontane basins..