The Yamizo Mountains, which is situated east of the Ashio Mountains, consists of four mountain blocks: the Ymizo, Torinoko, Keisoku and Tsukuba Mountain Blocks from north to south. The former three mountain blocks are made up mainly of Jurassic sedimentary complex. This sedimentary complex is subdivided into three tectonostratigraphic units: the Kasama, Takatori and Karasuyama Units in structurally ascending order.The Kasama Unit are composed mainly of upper Upper Jurassic sandstone and shale. Chert-clastic sequence occupies the lower part of this unit. Chert and siliceous shale are Middle Triassic and middle to upper Upper Jurasic, respectively. Uppermost Jurassic dark green shales containing many radiolarians are intercalated withiun the coarse clastic rocks.The Takatori Unit is subdividable into two parts; the lower part which is characterized by tectonic repetition of chert-clastic sequences composed of upper Lower Triassic siliceous claystone, Middle Triassic to lower Middle Jurassic chert,Middle Jurassic to middle Upper Jurassic siliceous shale and middle to upper Upper Jurassic clastic rocks, and the upper part consisting mainly of coarse clastic rocks containing Upper Jurassic shale. The Karasuyama Unit, which is distributed only in the western margin of the Torinoko Mountain Block, is made up of Upper Jurassic melange containing slabs and clasts of upper Middle Triassic to Middle Jurassic chert, lower Upper Jurassic siliceous shale,Upper Jurassic sandstone and shale. These lithologic and structural features suggest that the sedimentary complex in the Yamizo Mountains was formed by subduction-accretion tectonics in Late Jurassic time.Above mentioned three tectonostratigraphic units in the Yamizo Mountains are correlated with the units or complexes conducted by previous authors in the Tamba and Mino areas as follows. The Karasuyama Unit is correlated with parts of the Complex F and G of Tamba area, the Kanayama Unit of the central Mino area and melange unit of the Misogawa Complex of the eastern Mino area. The Takatori Unit corresponds with the Complex G of Tamba area, the Unit D of the central Miono area and the Misogawa and kyogatake Complexes of the eastern Mino area. The Kasama Unit may be correlated with the Yabuhara Complex of the eastern Mino area.The Ultra-Tamba Terrane and the Tamba-Mino Terrane are arranged in structurally descending order in the lnner Zone of Southwest Japan. This arrangement is observed in the east of the Itoigawa-Shizuoka Tectonic Line. The Onazawa Formation which is regarded as the eastern extension of the Ultra-Tamba Terrane, the sedimentary complex of the Ashio and Yamizo Mountains and the Upper Jurassic Nanjai Formation is arranged in structurally descending order.Eastward younging polarity is observable added to the southward younging polarity. This phenomena may be resulted from the oblique subduction of oceanic plate during Late Jurassic time.Chronological data of this study are derived from radiolarian fossils. List of radiolarian species which were identified in this study is shown as an appendix.Key words : chert clastic sequence, Jurassic, manganses carbonate nodules, radiolarians, sedimentary complex, Triassic, Yamizo Mountains.Thesis (Ph. D. in Science)--University of Tsukuba, (A), no. 2324, 2000.3.24Includes bibliographical referencesJurassic Sedimentary Complex of the Yamizo Mountains ~ 堀，常
