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Arakurayama Formation (Takeshita et al., 1960) Nagamori et al., 2003

Invalid synonym: Arakurayama Pyroclastic Member, Arakurayama Tuff Breccia Member, Shigarami Agglomerate, Shigarami Tuff Breccia, Mushikura Agglomerate, Konabe Formation

It had been treated as a member of Shigarami Formation.

• Type locality: Susohana river, Konabe - Machi, Kinasa, Nagano city, Nagano prefecture
• Type locality: Arakurayama camp field - Kamikusu river, Togakushi, Nagano city, Nagano prefecture
• Volcanic rocks
• Submarine volcano
• early Pliocene (4.2, 4.1 Ma, K-Ar)
• Contemporaneous heterotopic facies: middle Takafu Formation, Joshita Member
• Correlation: Togakushiyama Formation (Simultaneous multiple volcanos), Kumeji Pyroclastic Member
• Intruded by: Diorite Porphyry 2, Porphyrite, Hornblende andesite, Hypersthene and augite-bearing hornblende andesite

• Sedimentary facies (Upper, Andesite): Terrestrial
• Sedimentary facies: Marine
• Sedimentary facies: Submarine lava dome, Talus
• Lithofacies (Top, Minor): Volcanic conglomerate
• Lithofacies (Upper): Andesite lava, Volcanic breccia, Agglutinates
• Lithofacies (Middle): Dacite lava, Volcanic breccia, Pumiceous lapilli tuff
• Lithofacies (Lower): Basalt lava, Scoriaceous lapilli tuff, Intrusive rocks
• Sedimentary structures: Jigsaw fractures

• Thickness: ca. 500 - 1,800 m
• Upper limit: Conformity (Takafu Formation), Conformity, partly abut unconformity (Ogikubo Formation), Unconformity (Shimizu Formation), Abut unconformity (Sarumaru Formation)
• Lower limit: Interfingered (Takafu Formation)

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

• Distribution: Susohana river, Konabe - Machi, Kinasa, Nagano city, Nagano pref.; Arakurayama camp field - Kamikusu river, Togakushi, Nagano city, Nagano pref.; Inukaizawa, Nagano city, Nagano pref.; Mount Iizunayama - Ajimame, Ogawa city, Kamiminochi county, Nagano pref.
• Fossils: Balanus sp., Bryozoans
• Fossils (Shellfishes): Callista chinensis, Calyptraea sp., Chlamys cf. hatai, Glycymeris cf. yamasakii, Haliotis sp., Mercenaria cf. chitaniana, Monia sp., Notoacmaea asperulata

• Tanabe (2015) Jour. Geol. Soc. Japan, vol.121, no.8, pp.265-278, DOI
• Nagamori et al. (2003) Geology of the Togakushi District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 109p. (in Japanese with English abstract 3p.)
• Kato et al. (1989) Geology of the Omachi District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 111p. (in Japanese with English abstract 7p.)
• Kato and Akahane (1986) Geology of the Nagano District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 120p. (in Japanese with English abstract 5p.)