No. 5] Proc. Japan Acad., 60, Ser. B (1984) 99 27. Stratigraphic Comparison around the Sea of Japan By Teiichi KOBAYASHI,M. J. A. (Communicated, May 12, 1984) The upper Palaeozoic and Mesozoic formations and fossils of Japan are closely related to those of South Primorye, U.S.S.R., but later in the Cretaceous period South Korea was connected to West Japan at the Tsushima basin. Such a change took place by the drift- ing of the Japanese Islands from the continental side for more than twice. This is my prediction in 1935 here reconsidered with reference to additional data accumulated during a half century since then. 1) The Cambrian formation discovered in the Hanka block by Kropathkin in 1949 yields Lower and Middle Cambrian archaeo- cyathids, but no trilobite. Its basal conglomerate overlies a thick Pro- terozoic complex the older part of which is 830 myr. The archaeo- cyathids show that the sea was extended toward Tr,ansbikalia, but probably disconnected from Korea where Cambrian trilobites are abundant but no archaeocyathids. 2) No Upper Cambrian and Ordovician record is as yet found in either the Hanka-Suifung area or the Sikhota Alin, but the thick Tamginska series of the area contains a Silurian flora. Therefore the Chichibu geosyncline of Japan was connected with the Mongolian geosyncline through this area. The Silurian coralline fossils in the Kyeomipo limestone conglomerate in North Korea are telling a temporal marine ingression from the Japan sea side. 3) The thick Devonian formation of the Hanka area is rich in volcanic and pyroclastic rocks, showing the intrageosynclinal volcanism. It contains trilobites in the lower part, plants in the middle and f oraminif ers in the upper part. On the northwest side of Lake Hanka there exists the Middle Devonian Hetai formations at Mishan, Northeast China. 4) The Permo-Carboniferous formation is distributed widely in the Sikhota Alin and the Touman-Suifung area. Its thickness measures 8,000 m in the coastal belt and 14,000 m in the central belt of the mountains, where basic and intermediate rocks are rich. Fusulinids and other marine fossils from Visean to Upper Permian bear the Tethyan aspect, showing their connection toward the Japa- nese fauna. In the southwestern part of the coastal belt Carboni- ferous plant beds occur at a place and the Upper Permian formation directly overlies the older rocks at another. 100 T. KOBAYASHI [Vol. 60(B), At Kaishantun in the extreme southeast of Northeast China there are the late Upper Permian marine fossil beds and the plant beds whose flora bears the Cathaysian aspect. In the coastal belt of the Sikhota Alin land plants occur in the Lower Permian Vesnyansk formation. In the southern part of the belt plants are contained in the Sitsinsk formation above the Colaniella parva zone. These plants belong to the Angara flora. The Maiya flora from the Kitakami mountains, North Japan is Artinskian. This and the Kaishantun flora are related to the lower and upper Shihhotze flora respectively. There- fore in the Permian period the above areas were located just at the junction between the Angara and Cathaysia floral provinces. 5) In the vicinity of Vladiostok the Lower Triassic formation unconformably overlies the Permian as well as granite with the basal conglomerate containing granite boulders. The lowest fossil horizon is the Proptychites zone. Pleuromeia which occurs there in the Olenekian, was discovered also in Japan in the Kitakami mountains. The Middle Triassic formation conformably overlies the Lower Tri- assic and yields Paraceratites in the lower part and Daonella densisulcata at the top. In the north of Vladiostok the Ladinian sediment rests on the Permian directly. The Triassic fossils of Primorye are intimately related to the Japanese faunas. The sequence of the Inai-Zohoin series is thicker than 2,500 m, but in south Primorye the thickness of the correlative is reduced to a half. Geo- graphically the Maizuru zone, northwest Kyoto is the nearest counter part in Japan. 6) The Upper Triassic Mongugai series, about 1,600 m thick represents a paralic sequence of two cycles. Precisely speaking, the Carnic stage consists of the lower plant beds, 750 m thick and the neritic bivalve bearing upper part, 520-750 m thick ; the Noric stage of the lower plant beds, 300 m and the upper neritic sediments, 20 to 110 m in thickness. The C.arnian-Norian Mine series in West Japan reveals also two cycles of sedimentation, composed of the neritic Hirabara, the limnic Momonoki and the paralic Aso beds in ascending order. Their total thickness attains about 5,000 m. This is the typical molasse of the Akiyoshi orogeny. While volcanic material is absent in these Japanese Triassic, a large amount of pyroclastics contained in the Mongugai series, shows the metaorogenic volcanism behind the Akiyoshi folded mountains. The Mongugai fossils are so closely allied to the Mine-Kochigatani fauna and the Mine-Nariwa flora that there are many common species. The Phyoengyang coal-field in North Korea has been presumably in the western extention of the Akiyoshi folded mountains, because the Pyeongan and older formations were strongly disturbed by the No. 51 Stratigraphy around Japan Sea 101 Songnim crustal movement with the result that the late Triassic- early Jurassic D,aedong basins were brought to being in Korea. 7) The marine Jurassic formation extensive in the Soviet Far East is divided into two parts by the Middle Jurassic crustal move- ment. The lower division yields Liassic ammonites in the centrall part of the Sikhota Alin and marine bivalves in south Primorye in its lower part. Its upper part contains Inoceramus and the upper division Buchia and perisphincti. In West Japan Inoceramus of the retrosus group occurs in the Utano formation overlying the Liassic ammonite beds. Pliensbachian Amaltheus in Central Japan and Callovian Seymourites in the Tetori series of Central Japan and the Hashiura series in North Japan are two boreal genera of ammonites. In Korea some lakes existed in the Jurassic period. Near the end of the period the Daedong and older formations of South Korea were strongly deformed by the Daebo orogeny through which the Ogcheon folded mountains were produced on the northwestern side of the Precambrian Yongnam zone. On the other side of this zone the Tsushima basin was pro- duced by down warping at the beginning of the Cretaceous period. 8) The marine Cretaceous is extensive in the Soviet Far East. In the area under consideration it is divisible into five formations by discordances. The lowest is the Kuichevsk formation containing Corbicula aff. tetoriensis, Exogyra ryosekiensis, Ostrea of. yoshimo- ensis, Astarte sakawan~a and Onychiopsis elongata. As it is a corre- lative to the brackish Toyonishi formation, there must have been a narrow embayment extending from Primorye toward west Chugoku,. Japan. It was the progenitor of the Tsushima basin in which the Tvigonioides-Plicatounio fauna thrived. In the Touman-Suifung area T. kodairai was found at Talatzu near Hualung. In south Primorye the Suchansk formation is tuffaceous and contains Pteroti igonia allied to P. pocillif ormis and P. hokaidoana and Aralialn,ci f era. Its age is considered Barremian-Albian and correlated to the Uktusk formation in the Sikhota Aim. There it is overlain by the Larginsk formation of the Cenomanian age yielding Inoceramus concentric us nipponicns and I. hobetsuensis. This is in turn overlain by the Turonian Udominsk formation containing Par a- puzosia, Actaeonella orientalis and Inoceramus am,aksensis. Thus the sea was repeatedly flooded into the Sikhota Alin geosyncline from Sakhalin and Hokkaido until Turonian. The Oliginsk formation containing land plants overlies various formations with strong dis- cordance. It is chiefly composed of andesite and tuff in the lower part and liparite and tuff in the upper part. Among the repeated orogenic movements during the Cretaceous period the pre-Oliginsk 102 T. KOBAYASHF [Vol. 60(B), phase was paroxysmal, by which the geosyncline turned out land completely. 10) The Tertiary formations extensive in the coastal zone of the Sikhota Alin contain a large amount of volcanic and pyroclastic materials. The Vinsk coal-bearing beds are intercalated in the lower formation and contain land plants resembling the Yongdong flora in North Korea. The second is largely lacustrine deposits with middle Tertiary plant beds. The third is composed of the Plio- Pleistocene sediments, basalt and tuff. These three are separated by discordances indicating block movements at their intervals. In North Korea the Tertiary formation of Myeongcheon contains Miocene marine shells. There occurred block movements before and after the middle Tertiary formation. The Myeongcheon graben and Chilbosan horst along the coast of the Japan sea are two products of the latter movement. The marine Neogene deposits are distributed also on the east coast of South Korea and extensive in Japan. The sea of Japan in the Plio-Pleistocene age is similar to that of today at least on the Japanese and Korean sides. On the basis of salient facts enumerated above, I am led to the conclusion as follows : (1) The Mongolian and Chichibu geosynclines were confluent with each other at the Touman-Suifung area and the Sikhota Aim. The intra- geosynclinal volcanism there repeated during the Palaeozoic era. (2) The Chichibu geosyncline or the Akiyoshi folded mountains of Japan was shifted twice or more toward the Pacific ocean in the Mesozoic and later times. (3) The older Mesozoic Songnim and Akiyoshi folded mountains in North Korea and in the continental side of Japan respectively were on the same line and not very far removed from the Sikhota Alin in the older Mesozoic age. (4) Following the late Jurassic Daebo orogeny in the Ogcheon zone the Yoshimo embayment was brought to being on the east side of the Korean peninsula.