[ Top ] [ Japanese ]

Myozawabashi Formation (Morita, 1930 ex Yabe and Hatai, 1941) Yanagisawa and Yamamoto, 1998

Invalid synonym: Myozawa Formation, Kotamagawa Formation, Uchikawa? Formation, Takeya Formation

• Type locality: Myozawa bridge, Oguni city, Nishiokitama county, Yamagata prefecture
• Coherent formation
• Marine trasgression sediments
• early - middle Miocene (15.6 Ma, Myozawagawa Tuff Member; Shellfish fossils)
• Intruded by: Rhyolite dyke and lava domes, Andesite dyke
• Correlation: Lower Hibara Formation

• Sedimentary facies: Brackish, Marine
• Sedimentary facies: Inner sea
• Sedimentary facies: Tidal zone, Lagoon
• Sedimentary facies: Phreatomagmatic eruption at the shallow water bottom (Shallower than a few hundreds m).
• Lithofacies: Sandstone, Mudstone
• Lithofacies (Minor): Rhyolitic volcanic conglomerate, Volcanic sandstone, Basaltic scoraceous lapillistone, Accretionary lapilli tuff, Volcanic sandstone
• Sedimentary structures: Parallel stratificaiton, Low angle cross stratification, Bioturbation

• Thickness: ca. 0 - 1,060 m
• Upper limit: Bottom of shellfish fossil-bearing calcareous sandstone or tuffaceous sandstone showing cross stratification
• Upper limit: Conformity (Numazawa Formation)
• Lower limit: Conformity (Meganebashi Formation), Unconformity (Hakonokuchi Formation)

------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown

• Distribution: Myozawa bridge - Kanomizu - Shirakozawa - Yokokawa river - Shirakawa river - Higashizawa - Shirafuzawa?, Oguni city, Nishiokitama county, Yamagata pref.; Kotaru river, Yonezawa city, Yamagata pref.
• Fossils (Yatsuo-Kadonosawa fauna): Crassostrea gravitesta, Vicarya yokoyamai, Striarca uetsukiensis, Vicaryella sp., Cerithideopsilla sp., Chicoreus asanoi
• Fossils (Pollen): Artemisia, Ercaceae, Ilex, Acer, Rhus, Liquidambar, Zelkova, Ulmus, Quercus, Castanopsis, Fagus, Castanea, Corylus, Carpinus, Betula, Alnus, Carya, Pterocarya, Juglans, Salix, Taxodiaceae, Dacrydium, Chenopodiaceae, Kandelia, Sapium

• Furukawa et al. (2018) Geology of the Azuma Yama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 74p. (in Japanese with English abstract 3p.)
• Yamanoi et al. (2008) Jour. Geol. Soc. Japan, vol.114, no.5, pp.262-266 DOI
• Yanagisawa and Yamamoto (1998) Geology of the Tamaniwa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 94p. (in Japanese with English abstract 4p.)
• Takahashi et al. (1996) Geology of the Iidesan District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 52p. (in Japanese with English abstract 3p.)