Y4 Member

[ Top ] [ Japanese ]

Y₄ Member

Type locality: Oshima city, Tokyo
Volcanic rocks
Stratovolcano, Caldera volcano
Holocene (AD 1421?)

Sedimentary facies (Minor): Flank crater deposit, Scoria cone, Tuff ring, Explosion breccia
Lithofacies: Low-alkaline tholeiite series
Lithofacies: Pigeonite series
Lithofacies (Upper): Volcanic ash
Lithofacies (Upper, Minor): Scoriaceous lapilli
Lithofacies (Lower): Scoria, Lava
Lithofacies (Flank crater): Spatter, Welded spatter, Lava, Lapilli tuff, Tuff breccia
Paleocurrent (Lower): East-southeast

Mode of eruption: Magmatic, Phreatomagmatic

Yuba Formation
[ Upper ]
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Y₁ Member
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Y₂ Member
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Y₃ Member
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Y₄ Member
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Y₅ Member
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Y₆ Member
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[ Lower ]

Post-caldera stage
[ Upper ]
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Yuba Formation
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Nomashi Formation
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[ Lower ]

Oshima volcano
[ Upper ]
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Post-caldera stage
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Syn-caldera stage
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Pre-caldera stage
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[ Lower ]

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

Distribution: Mabushi - Oana - Koana - Takenohira - Imasaki, Oshima city, Tokyo

Isshiki (1984) Geology of the Oshima District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 133p. (in Japanese with English abstract 5p.)