[ Top ] [ Japanese ]

Yugoya Formation (Tokunaga and Tanai, 1954)

Invalid synonym: Yago Formation, Shirakawa Formation

• Type locality: Shirakawa river, Yugoya, Iide city, Nishiokitama county, Yamagata prefecture
• Coherent formation
• Marine regression sediments
• middle - late Miocene (Diatoms, Calcareous nannofossils)
• Correlation: Onnagawa Formation, Teradomari Formation

• Sedimentary facies: Marine
• Sedimentary facies (Pyroclastic rocks): Gravity current deposit originated in the rhyolite lava dome
• Lithofacies: Mudstone, Sandy mudstone
• Lithofacies (Minor): Rhyolite tuff (Bentonite), Lapilli tuff, Volcanic sandstone, Tuff
• Sedimentary structures (Rhyolite tuff): Flute cast
• Paleocurrent: Northwest, West-northwest

• Source (Pyroclastic rocks): The rhyolite body at the south of Sugo bridge in Hirogawara river
• Thickness: ca. 130 - 550 m
• Upper limit: Bottom of the sandstone and conglomerate-dominant horizon
• Upper limit: Conformity, partly unconformity (Utsutoge Formation)
• Lower limit: Bottom of the horizon composed of dark black mudstone, Top of the rhyolitic pyroclastic rocks.
• Lower limit: Transitional (Numazawa Formation)

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

• Distribution: Shirakawa river - Oishizawa - Morinokoshi river, Yugoya, Iide city, Nishiokitama county, Yamagata pref.; Numazawa, Oguni city, Nishiokitama county, Yamagata pref.
• Fossils: Diatoms, Trace fossils (Teichichnus isp.)

• 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.)