[ Top ] [ Japanese ]
Somma Chiba et al., 2000
- Type locality: Nishinoshima island - Nakanoshima island - Chiburijima island, Oki county, Shimane prefecture
- Volcanic rocks
- Somma, Parasitic cone
- late Miocene
- Upper: late Miocene (5.8 - - 5.6 Ma, K-Ar)
- Lower: late Miocene (6.3 - 5.8 Ma, K-Ar)
- Correlation (Lower): Shimazushima Formation
- Sedimentary facies (Lower): Shallow marine
- Sedimentary facies (Upper, Minor): Caldera wall collapse deposits
- Sedimentary facies (Lower): Hyaloclastite
- Sedimentary facies (Lower, Minor): Pyroclastic cone, Tuff ring
- Sedimentary facies (Lower, Minor): Pyroclastic surge deposits, Pyroclastic fall deposits
- Lithofacies (Upper): Mafic trachyte lava, Felsic trachyite lava
- Lithofacies (Upper, Minor): Volcanic breccia
- Lithofacies (Lower): Trachybasalt lava, Basaltic trachyandesite lava, Volcanish ash fall, Scoria
- Lithofacies (Lower, Minor): Trachyte pumiceous lapilli tuff, Tuff, Agglutinate, Agglomerate
- Sedimentary structures (Upper, Felsic trachyte): Coloumnar joint
- Mode of eruption: Phreatomagmatic
- Distribution (Pyroclastic cone, Diameter): A few hundred m
- Distribution (Pyroclastic cone, Height): A few dozen m
- Upper limit (Upper part): Unconformity (Chichiimisaki Formation, Uzuka Basalt)
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Nishinoshima island, Nishinoshima city, Oki county, Shimane pref.; Nakanoshima island, Ama city Oki county, Shimane pref.; Chiburijima island, Chibu city, Oki county, Shimane
- Distribution (Parasitic cone): Mount Takasakiyama, Nishinoshima city, Oki county, Shimane pref.; Mount Atodosan - Mount Tsunoyama - Mount Tadayama - Mount Kinkojisn - Cape Chichiimisaki - Matsushima island - Omoriyama island, Ama city, Oki county, Shimane pref.; Kurii - Kori - Shiroshima island - Ohakajima island, Chibu city, Oki county, Shimane pref.
- Chiba et al. (2000) Geology of the Urago District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 74p. (in Japanese with English abstract 3p.)