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Itahana Formation (Fujimoto and Kobayashi, 1938) Watabe, 1952

Originally included in Takasaki Group as a member.

• Type locality: Gangyo river, Takasaki city, Gunma prefecture
• Coherent formation
• late Miocene (ca. 11 Ma -)
• Intruded by: Basaltic andesite sill, Dacite sill

• Sedimentary facies: Delta
• Sedimentary facies (Upper): Fluvial
• Sedimentary facies (Tate Tuff): Dry terrestrial
• Sedimentary facies (Bottom): Shallow marine
• Lithofacies (Top): Lapilli tuff
• Lithofacies (Upper): Conglomerate
• Lithofacies (Upper, Minor): Siltstone, Siliceous tuff, Lignite
• Lithofacies (Lower): Conglomerate
• Lithofacies (Lower, Minor): Sandstone, Siltstone
• Lithofacies (Bottom): Sandstone, Interbedded sandstone and siltstone
• Sedimentary structures (Upper): Imbrication
• Paleocurrent (Upper): Southeast to Northwest, South to North, Southwest to Northeast

• Thickness (Top, Lapilli tuff): 150 - 250 m
• Thickness (Upper): 680 - 700 m
• Thickness (Lower): 300 - 700 m
• Upper limit (Akima Formation): Bottom of the horizon containing pyroxene andesite boulders
• Upper limit: Unconformity (Koneyama Formation, Kirizumi Formation), Angular unconformity (Akima Formation, Aimagawa Formation, Nodono Formation)
• Lower limit: Conformity (Haraichi Formation)

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

• Distribution: Gangyo river, Takasaki city, Gunma pref.
• Fossils (Upper): Trace fossils (Rosselia isp.)
• Fossils (Tate Tuff): Erect tree trunk
• Fossils (Lower): Sirenia, Plants
• Fossils (Lower, Shellfishes): Glycymeris cisshuensis, Ostrea gravitesta
• Tephra: Tate Tuff, Yamaguchi Tuff, Nakazeki Tuff, Masudagawabashi Tuff

• Tanaka et al. (2013) Jour. Geol. Soc. Japan, vol.119, no.1, pp.17-24 DOI
• Geshi and Takeuchi (2012) Geology of the Haruna San District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 79p. (in Japanese with English abstract 3p.)